A handbook of systematic botany (part 2 of 4)

Preface

The present translation of Dr. E. Warming’s Haandbog i den Systematiske Botanik is taken from the text of the 3rd Danish Edition (1892), and from Dr. Knoblauch’s German Edition (1890), and the book has been further enriched by numerous additional notes which have been kindly sent to me by the author. Dr. Warming’s work has long been recognised as an original and important contribution to Systematic Botanical Literature, and I have only to regret that the pressure of other scientific duties has delayed its presentation to English readers. Dr. Warming desires me to record his high appreciation of the careful translation of Dr. Knoblauch, and his obligation to him for a number of corrections and improvements of which he has made use in the 3rd Danish Edition. In a few instances I have made slight additions to the text; these, however, appear as footnotes, or are enclosed in square brackets.

In the present Edition the Thallophytes have been revised and rearranged from notes supplied to me by Dr. Knoblauch, to whom I am indebted for the Classification of the Fungi, according to the more recent investigations of Brefeld. The Bacteria have been revised by Dr. Migula, the Florideæ rearranged after Schmitz, and the Taphrinaceæ after Sadebeck. The main body of the text of the Algæ and Fungi remains as it was originally written by Dr. Wille and Dr. Rostrup in the Danish Edition, though in many places considerable alterations and additions have been made. For the sake of comparison a tabular key to the Classification adopted in the Danish Edition is given in the Appendix.

In the Angiosperms I have retained the sequence of orders in the Danish original, and have not rearranged them according to the systems more familiar to English students. In any rearrangement much of the significance of Dr. Warming’s valuable and original observations would have been lost, and also from a teacher’s point of view I have found this system of great value. Although at present it may not be completely satisfactory, yet as an attempt to explain the mutual relationships, development and retrogression of many of the orders, it may be considered to have a distinct advantage over the more artificial systems founded upon Jussieu’s Divisions of Polypetalæ, Gamopetalæ, and Apetalæ.

With reference to the principles of the systematic arrangement adopted, I may here insert the following brief communication from the author (dated March, 1890), which he has requested me to quote from the preface of Dr. Knoblauch’s edition:--“Each form which, on comparative morphological considerations, is clearly less simple, or can be shown to have arisen by reduction or through abortion of another type having the same fundamental structure, or in which a further differentiation and division of labour is found, will be regarded as younger, and as far as possible, and so far as other considerations will admit, will be reviewed later than the ‘simpler,’ more complete, or richer forms. For instance, to serve as an illustration: EPIGYNY and PERIGYNY are less simple than HYPOGNY; the Epigynous Sympetalæ, Choripetalæ, Monocotyledones are, therefore, treated last, the Hydrocharitaceæ are considered last under the Helobieæ, etc. ZYGOMORPHY is younger than ACTINOMORPHY; the Scitamineæ and Gynandræ therefore follow after the Liliifloræ, the Scrophulariaceæ after the Solanaceæ, Linaria after Verbascum, etc. FORMS WITH UNITED LEAVES indicate younger types than those with free leaves; hence the Sympetalæ come after the Choripetalæ, the Sileneæ after the Alsineæ, the Malcaceæ after the Sterculiaceæ and Tiliaceæ, etc.

“ACYCLIC (spiral-leaved) flowers are older than cyclic (verticillate-leaved) with a definite number, comparing, of course, only those with the same fundamental structure. The Veronica-type must be considered as younger, for example, than Digitalis and Antirrhinum, these again as younger than Scrophularia; Verbascum, on the contrary, is the least reduced, and therefore considered as the oldest form. Similarly the one-seeded, nut-fruited Ranunculaceæ are considered as a later type (with evident abortion) than the many-seeded, folicular forms of the Order; the Paronychieæ and Chenopodiaceæ as reduced forms of the Alsineæ type; and the occurrence of few seeds in an ovary as generally arising through reduction of the many-seeded forms. The Cyperaceæ are regarded as a form derived from the Juncaceæ through reduction, and associated with this, as is so often the case, there is a complication of the inflorescence; the Dipsacaceæ are again regarded as a form proceeding from the Valerianaceæ by a similar reduction, and these in their turn as an offshoot from the Caprifoliaceæ, etc. Of course these principles of systematic arrangement could only be applied very generally; for teaching purposes they have often required modification.”

In preparing the translation considerable difficulty has been experienced in finding a satisfactory rendering of several terms which have no exact equivalent in English. I may here especially mention the term Vorblatt (Forblad) which I have translated by the term bracteole, when it clearly applied to the first leaf (or leaves) on a pedicel; but in discussing questions of general morphology a term was much needed to include both vegetative and floral shoots, and for this I have employed the term “Fore-leaf.” Also, the term “Floral-leaf” has been adopted as an equivalent of “Hochblatt,” and the term “bract” has been limited to a leaf subtending a flower. I have followed Dr. E. L. Mark in translating the word “Anlage” by “Fundament.”

At the end of the book will be found a short appendix giving an outline of some of the earlier systems of Classification, with a more complete account of that of Hooker and Bentham.

In a book of this character it is almost impossible to avoid some errors, but it is hoped that these will be comparatively few. In correcting the proof-sheets I have received invaluable assistance from Dr. Warming and Dr. Knoblauch, who have kindly read through every sheet, and to whom I am greatly indebted for many criticisms and suggestions. I have also to thank Mr. I. H. Burkill for his kind assistance in looking over the proofs of the Monocotyledons and Dicotyledons, and Mr. Harold Wager for kindly reading through the proofs of the Algæ and Fungi. My thanks are also especially due to Mr. E. L. Danielsen, and I wish to take this opportunity of acknowledging the very considerable help which I have received from him in translating from the Original Danish. M. C. POTTER. January, 1895.

BEING THE SYSTEM OF CLASSIFICATION ADOPTED IN THE PRESENT VOLUME.

(The Algæ and Fungi rearranged in co-operation with Dr. E. Knoblauch, the other Divisions as in the 3rd Danish Edition.)

PAGE

DIVISION I. THALLOPHYTA 4

A. Sub-Division. Myxomycetes, Slime-Fungi 5

B. Sub-Division. Algæ 8

Class 1. SYNGENETICÆ 14

„ 2. DINOFLAGELLATA 16

„ 3. DIATOMEÆ 18

„ 4. SCHIZOPHYTA 22

Family 1. Schizophyceæ 22

„ 2. Bacteria 26

Class 5. CONJUGATÆ 41

„ 6. CHLOROPHYCEÆ 46

Family 1. Protococcoideæ 47

„ 2. Confervoideæ 53

„ 3. Siphoneæ 59

Class 7. CHARACEÆ 64

„ 8. PHÆOPHYCEÆ (OLIVE-BROWN SEAWEEDS) 68

Family 1. Phæosporeæ 68

„ 2. Cyclosporeæ 73

Class 9. DICTYOTALES 76

„ 10. RHODOPHYCEÆ (RED SEAWEEDS) 77

Family 1. Bangioideæ 77

„ 2. Florideæ 78

C. Sub-Division. Fungi 84

Class 1. PHYCOMYCETES 96

Sub-Class 1. Zygomycetes 96

„ 2. Oomycetes 100

Family 1. Entomophthorales 102

„ 2. Chytridiales 102

„ 3. Mycosiphonales 104

Class 2. MESOMYCETES 108

Sub-Class 1. Hemiasci 108

„ 2. Hemibasidii 109

Class 3. MYCOMYCETES (HIGHER FUNGI) 114

Sub-Class 1. Ascomycetes 114

Series 1. Exoasci 116

„ 2. Carpoasci 118

Family 1. Gymnoascales 118

„ 2. Perisporiales 119

„ 3. Pyrenomycetes 125

„ 4. Hysteriales 132

„ 5. Discomycetes 132

„ 6. Helvellales 136

Ascolichenes 136

Sub-Class 2. Basidiomycetes 144

Series 1. Protobasidomycetes 145

„ 2. Autobasidiomycetes 157

Family 1. Dacryomycetes 159

„ 2. Hymenomycetes 159

„ 3. Phalloideæ 172

„ 4. Gasteromycetes 173

Basidiolichenes 176

Fungi Imperfecti 176

DIVISION II. MUSCINEÆ (MOSSES) 181

Class 1. HEPATICÆ 188

Family 1. Marchantieæ 190

„ 2. Anthoceroteæ 191

„ 3. Jungermannieæ 191

Class 2. MUSCI FRONDOSI 192

Family 1. Sphagneæ 193

„ 2. Schizocarpeæ 195

„ 3. Cleistocarpeæ 195

„ 4. Stegocarpeæ 195

DIVISION III. PTERIDOPHYTA 198

Class 1. FILICINÆ 205

Sub-Class 1. Filices 205

Family 1. Eusporangiatæ 210

„ 2. Leptosporangiatæ 212

Sub-Class 2. Hydropterideæ 215

Class 2. EQUISETINÆ (HORSETAILS) 221

Sub-Class 1. Isosporous Equisetinæ 221

„ 2. Heterosporous Equisetinæ 225

Class 3. LYCOPODINÆ (CLUB MOSSES) 226

Sub-Class 1. Lycopodieæ 226

„ 2. Selaginelleæ 228

TRANSITION FROM THE CRYPTOGAMS TO THE PHANEROGAMS 234

Asexual Generation of the Cormophytes 234

Sexual Generation; Fertilisation 243

DIVISION IV. GYMNOSPERMÆ 251

Class 1. CYCADEÆ (CYCADS) 252

„ 2. CONIFERÆ (PINE-TREES) 255

Family 1. Taxoideæ 259

„ 2. Pinoideæ 262

Class 3. GNETEÆ 270

Fossil Gymnosperms 271

DIVISION V. ANGIOSPERMÆ 273

Class 1. MONOCOTYLEDONES 274

Family 1. Helobieæ 278

„ 2. Glumifloræ 283

„ 3. Spadicifloræ 297

„ 4. Enantioblastæ 308

„ 5. Liliifloræ 309

„ 6. Scitamineæ 323

„ 7. Gynandræ 328

Class 2. DICOTYLEDONES 334

Sub-Class 1. Choripetalæ 337

Family 1. Salicifloræ 337

„ 2. Casuarinifloræ 339

„ 3. Quercifloræ 340

„ 4. Juglandifloræ 349

„ 5. Urticifloræ 351

„ 6. Polygonifloræ 358

„ 7. Curvembryæ 363

„ 8. Cactifloræ 375

„ 9. Polycarpicæ 377

„ 10. Rhœadinæ 393

„ 11. Cistifloræ 406

„ 12. Gruinales 416

„ 13. Columniferæ 421

„ 14. Tricoccæ 430

„ 15. Terebinthinæ 435

„ 16. Aesculinæ 439

„ 17. Frangulinæ 443

„ 18. Thymelæinæ 448

„ 19. Saxifraginæ 451

„ 20. Rosifloræ 456

„ 21. Leguminosæ 466

„ 22. Passiflorinæ 475

„ 23. Myrtifloræ 482

„ 24. Umbellifloræ 490

„ 25. Hysterophyta 498

Sub-Class 2. Sympetalæ 504

A. Pentacyclicæ 506

Family 26. Bicornes 506

„ 27. Diospyrinæ 510

„ 28. Primulinæ 511

B. Tetracyclicæ 514

Family 29. Tubifloræ 514

„ 30. Personatæ 517

„ 31. Nuculiferæ 531

„ 32. Contortæ 541

„ 33. Rubiales 548

„ 34. Dipsacales 556

„ 35. Campanulinæ 560

„ 36. Aggregatæ 564

APPENDIX 574

INDEX 593

CORRIGENDA.

Page 9, line 12 from top, for Hydrodicton read Hydrodictyon. „ 14, lines 1 and 2 from top, for as in the preceding case read in this case. „ 14, „ 2 and 15 from top, for zygote read oospore. „ 88, line 15 from bottom, for Periphyses read periphyses. „ 124, „ 7 „ „ for Chæromyces read Choiromyces. „ 142, „ 2 „ „ and in Fig. 137, for Bœomyces read Bæomyces. „ 152, „ 2 „ top, for Pirus read Pyrus. „ 152, „ 5 „ „ for Crategus read Cratægus. „ 216, Fig. 215, for Salvina read Salvinia. „ 306, line 6 from top, for Pista read Pistia. „ 316, „ 26 „ „ after Dracæna insert a comma. „ 337, „ 13 „ „ for end read beginning. „ 483, „ 11 „ bottom, for Lagerstrœmia read Lagerstrœmeria.

For ä, ö and ü read æ, œ and ue throughout.

The following are not officinal in the British Pharmacopœia:--page 316, Dracæna (Dragon’s-blood), Smilax glabra; p. 321, “Orris-root”; p. 326, species of Curcuma, Alpinia officinarum; p. 333, Orchis-species (“Salep”). On page 296, par. 4, only Pearl Barley is offic. in the Brit. Phar.

CLASSIFICATION OF THE VEGETABLE KINGDOM.

The Vegetable Kingdom is arranged in 5 Divisions.

Division I.--=Thallophyta=, =Stemless Plants=, or those which are composed of a “thallus,” i.e. organs of nourishment which are not differentiated into root (in the sense in which this term is used among the higher plants), stem, or leaf. Vascular bundles are wanting. Conjugation and fertilisation in various ways; among most of the Fungi only vegetative multiplication.

In contradistinction to the Thallophytes all other plants are called “Stem-plants” (“Cormophyta”), because their shoots are leaf-bearing stems. The name Thallophyta (Stemless-plants) is to some extent unsuitable, since many of the higher Algæ are differentiated into stem and leaf.

The Thallophytes are again separated into 3 sub-divisions, namely:

Sub-Division =A.=--=Myxomycetes, Slime-Fungi=, with only 1 class.

Sub-Division =B.=--=Algæ=, with 10 classes: Class 1. Syngeneticæ. „ 2. Dinoflagellata, Peridinea. „ 3. Diatomeæ, Diatoms. „ 4. Schizophyta, Fission Algæ. „ 5. Conjugatæ. „ 6. Chlorophyceæ, Green Algæ. „ 7. Characeæ, Stone-worts. „ 8. Phæophyceæ, Brown Algæ. „ 9. Dictyotales. „ 10. Rhodophyceæ, Red Algæ.

Sub-Division =C.=--=Fungi=, with 3 classes: Class 1. Phycomycetes. „ 2. Mesomycetes. „ 3. Mycomycetes, Higher Fungi.

Division II.--=Bryophyta or Muscineæ, Mosses.= These have leaf-bearing shoots, but neither true roots nor vascular bundles. The lowest Mosses have, however, a thallus. Fertilisation is accomplished by means of self-motile, spirally coiled spermatozoids, through the agency of water. From the fertilised oosphere a “fruit-body” (capsule) with unicellular organs of reproduction (spores) is produced. The spore on germination gives rise to the vegetative system, which bears the organs of sexual reproduction; and this system is divided into two stages--the protonema, and the leaf-bearing plant produced on it.

Alternation of generations:

I. The protonema and the entire nutritive system which bears the organs of sexual reproduction. II. The capsule-like sporangium, with spores. 2 Classes: 1. Hepaticæ, Liverworts. 2. Musci, Leafy Mosses.

Division III.--=Pteridophyta or Vascular Cryptogams=, =Fern-like Plants= having leaf-bearing shoots, true roots, and vascular bundles with tracheides and sieve-tubes. Fertilisation as in the Mosses. From the fertilised oosphere the leaf-bearing shoot arises, which bears on its leaves the reproductive organs, the spores, in capsule-like sporangia. From the germination of the spore a small prothallium is formed, which bears the sexual reproductive organs.

Alternation of generations:

I. Prothallium with organs of sexual reproduction. II. Leaf-bearing shoot with capsule-like sporangia. 3 Classes: 1. Filicinæ, True Ferns. 2. Equisetinæ, Horsetails. 3. Lycopodinæ, Club-mosses.

Division IV.--=Gymnospermæ.= The vegetative organs are in the main similar to those in the 3rd Division; special shoots are modified into flowers for the service of reproduction. From the oosphere, which is fertilised by means of the pollen-tube, the leaf-bearing plant is derived; this passes the first period of its life as an embryo in the seed, and continues its development when the germination of the seed takes place. The organs corresponding to the spores of the two preceding Divisions, are called respectively the pollen-grain and embryo-sac. The pollen-grains are multicellular; i.e. they contain an indistinct prothallium. In the embryo-sac a prothallium, rich in reserve material (endosperm), with female organs of reproduction, is developed BEFORE FERTILISATION. The pollen-grains are carried by means of the wind to the ovules; these enclose the embryo-sac, and are situated on the open fruit-leaf (carpel), which has no stigma.

Alternation of generations:

I. Prothallium = Endosperm in ovule. II. Leaf-bearing plant, with flowers which produce the pollen-sac and ovule. 3 Classes: 1. Cycadeæ. 2. Coniferæ. 3. Gnetaceæ.

Division V.--=Angiospermæ=. The members of this group are very similar to those of Division IV. The ovules are, however, encased in closed fruit-leaves (ovary), which have a special portion (stigma) adapted for the reception and germination of the pollen-grains. The pollen-grains are bicellular, but with only a membrane separating the two nuclei; they are carried to the stigma by animals (chiefly insects), by the wind, or by some other means. Endosperm is not formed till AFTER FERTILISATION. Alternation of generations in the main as in the Gymnosperms, but less distinct; while the sexual generation, the prothallium, with the organs of fertilisation, is also strongly reduced.

2 Classes:[1] 1. Monocotyledones. Embryo with one seed-leaf. 2. Dicotyledones. Embryo with two seed-leaves.

For a long time the vegetable kingdom has been divided into. CRYPTOGAMS (so called because their organs of reproduction remained for some time undiscovered), and PHANEROGAMS or Flowering-plants which have evident sexual organs.

The first three divisions belong to the Cryptogams, and the third and fourth divisions to the Phanerogams. This arrangement has no systematic value, but is very convenient in many ways.

The Cryptogams are also known as Spore-plants, since they multiply by unicellular organs (spores), and the Phanerogams in contradistinction are called Seed-plants (Spermaphyta), since they multiply by seeds, multicellular bodies, the most important part of which is the embryo (a plant in its infancy). Mosses, Ferns, and Gymnosperms are together known as Archegoniatæ, since they possess in common a female organ of distinct structure, the Archegonium.

DIVISION I.

THALLOPHYTA.

The thallus in the simplest forms is unicellular; in the majority, however, it is built up of many cells, which in a few instances are exactly similar; but generally there is a division of labour, so that certain cells undertake certain functions and are constructed accordingly, while others have different work and corresponding structure. Vessels or similar high anatomical structures are seldom formed, and the markings on the cell-wall are with few exceptions very simple. The Myxomycetes occupy quite an isolated position; their organs of nourishment are naked masses of protoplasm (plasmodia).

As regards the external form, the thallus may be entirely without special prominences (such as branches, members), but when such are present they are all essentially alike in their origin and growth, that is, disregarding the hair-structures which may be developed. A shoot of a Seaweed or of a Lichen, etc., is essentially the same as any other part of the plant; only among the highest Algæ (Characeæ, certain Siphoneæ, Sargassum, and certain Red Seaweeds) do we find the same differences between the various external organs of the plant body as between stem and leaf, so that they must be distinguished by these names.

Roots of the same structure and development as in the Seed-plants are not found, but organs of attachment (rhizoids and haptera) serve partly the biological functions of the root.

SYSTEMATIC DIVISION OF THE THALLOPHYTES. To the Thallophytes belong three sub-divisions--Slime-Fungi, Algæ, and Fungi. Formerly the Thallophytes were divided into Algæ, Fungi, and Lichens. But this last group must be placed among the Fungi, since they are really Fungi, which live symbiotically with Algæ. The Slime-Fungi must be separated from the true Fungi as a distinct subdivision. The Algæ possess a colouring substance, which is generally green, brown, or red, and by means of which they are able to build up organic compounds from carbonic acid and water. The Bacteria, especially, form an exception to the Algæ in this respect; like the Fungi and Slime-Fungi they have as a rule no such colouring material, but must have organic carbonaceous food; these plants form no starch, and need no light for their vegetation (most Fungi require light for fructification). The Myxomycetes, Bacteria, and Fungi derive their nourishment either as saprophytes from dead animal or vegetable matter, or as parasites from living animals or plants (hosts), in which they very often cause disease.

A remark, however, must be made with regard to this division. Among the higher plants so much stress is not laid upon the biological relations as to divide them into “green” and “non-green”; Cuscuta (Dodder), a parasite, is placed among the Convolvulaceæ, Neottia and Corallorhiza, saprophytes, belong to the Orchidacere, although they live like Fungi, yet their relations live as Algæ. In the same manner there are some colourless parasitic or saprophytic forms among the Algæ, and stress must be laid upon the fact that not only the Blue-green Algæ, but also the Bacteria, which cannot assimilate carbonic-acid, belong to the Algæ group, Schizophyceæ. The reason for this is that systematic classifications must be based upon the relationship of form, development, and reproduction, and from this point of view we must regard the Bacteria as being the nearer relatives of the Blue-green Algæ. All the Thallophytes, which are designated Fungi (when the entire group of Slime-Fungi is left out), form in some measure a connected series of development which only in the lower forms (Phycomycetes) is related to the Algæ, and probably through them has taken its origin from the Algæ; the higher Fungi have then developed independently from this beginning. The distinction of colour referred to is therefore not the only one which separates the Algæ from the Fungi, but it is almost the only characteristic mark by which we can at once distinguish the two great sub-divisions of the Thallophytes.

The first forms of life on earth were probably “Protistæ,” which had assimilating colour material, or in other words, they were Algæ because they could assimilate purely inorganic food substances, and there are some among these which belong to the simplest forms of all plants. Fungi and Slime-Fungi must have appeared later, because they are dependent on other plants which assimilate carbon.[2]

Sub-Division I.--=MYXOMYCETES, SLIME-FUNGI.=

The Slime-Fungi occupy quite an isolated position in the Vegetable Kingdom, and are perhaps the most nearly related to the group of Rhizopods in the Animal Kingdom. They live in and on organic remains, especially rotten wood or leaves, etc., on the surface of which their sporangia may be found.

They are organisms without chlorophyll, and in their vegetative condition are masses of protoplasm without cell-wall (plasmodia). They multiply by means of spores, which in the true Slime-Fungi[3] are produced in sporangia, but in some others[4] free. The spores are round cells (Fig. 1 a) which in all the true Slime-Fungi are surrounded by a cell-wall. The wall bursts on germination, and the contents float out in the water which is necessary for germination. They move about with swimming and hopping motions like swarmspores (e, f), having a cilia at the front end and provided with a cell-nucleus and a pulsating vacuole. Later on they become a little less active, and creep about more slowly, while they continue to alter their form, shooting out arms in various places and drawing them in again (g, h, i, k, l, m); in this stage they are called Myxamœbæ.

The Myxamœba grows whilst taking up nourishment from the material in which it lives, and multiplies by division. At a later stage a larger or smaller number of Myxamœbæ may be seen to coalesce and form large masses of protoplasm, plasmodia, which in the “Flowers of Tan” may attain the size of the palm of a hand, or even larger, but in most others are smaller. The plasmodia are independent, cream-like masses of protoplasm, often containing grains of carbonate of lime and colouring matter (the latter yellow in the Flowers of Tan). They creep about in the decaying matter in which they live, by means of amœboid movements, internal streamings of the protoplasm continually taking place; finally they creep out to the surface, and very often attach themselves to other objects, such as Mosses, and form sporangia (Fig. 2). These are stalked or sessile and are generally cylindrical (Fig. 3), spherical or pear-shaped (Fig. 4); they rarely attain a larger size than that of a pin’s head, and are red, brown, white, blue, yellow, etc., with a very delicate wall. In some genera may be found a “Capillitium” (Fig. 4 cp), or network of branched fine strands between the spores. Flowers of Tan (Fuligo septica) has a fruit-body composed of many sporangia (an Æthalium), which has the appearance of flat, irregular, brown cakes, inside the fragile external layer of which a loose powder, the spores, is found. It generally occurs on heaps of tanners’ bark, and appears sometimes in hot-beds in which that material is used, and is destructive by spreading itself over the young plants and choking them.

All the motile stages may pass into resting stages, the small forms only surrounding themselves with a wall, but the large ones at the same time divide in addition into polyhedral cells. When favourable conditions arise, the walls dissolve and the whole appears again as a naked (free-moving) mass of protoplasm.

To the genuine Slime-Fungi belong: Arcyria, Trichia, Didymium, Physarum, Stemonitis, Lycogala, Fuligo, Spumaria, Reticularia.

Some genera wanting a sporangium-wall belong to the Slime-Fungi: Ceratiomyxa, whose fruit-body consists of polygonal plates, each bearing stalked spores; Dictyostelium, in which the swarm-stage is wanting and which has stalked spores. Plasmodiophora brassicæ preys upon the roots of cabbages and other cruciferous plants, causing large swellings. Pl. alni causes coral-shaped outgrowths on the roots of the Alder (Alnus). Phytomyxa leguminosarum may be found in small knobs (tubercles) on the roots of leguminous plants. It is still uncertain whether it is this Fungus or Bacteria which is the cause of the formation of these tubercles.

Sub-Division II.--=ALGÆ=.

=Mode of Life.= The Algæ (except most of the Bacteria) are themselves able to form their organic material by the splitting up of the carbonic acid contained in the water, or air in some cases, and for this purpose need light. The majority live in water, fresh or salt, but many are present on damp soil, stones, bark of trees, etc.

With the exception of the Bacteria, no saprophytes have actually been determined to belong to this group, and only very few true parasites (for instance, Phyllosiphon arisari, Mycoidea, etc.), but a good many are found epiphytic or endophytic on other Algæ, or water plants, and on animals (for instance, certain Schizophyceæ and Protococcoideæ; Trichophilus welckeri in the hairs of Bradypus, the Sloth), and several species in symbiotic relation to various Fungi (species of Lichen), to Sponges (e.g. Trentepohlia spongiophila, Struvea delicatula), and to sundry Infusoria and other lower animals as Radiolarias, Hydra, etc. (the so-called Zoochlorella and Zooxantella, which are perhaps partly stages in development of various Green and Brown Algæ).

=Vegetative Organs.= The cells in all the Algæ (excepting certain reproductive cells) are surrounded by a membrane which (with the exception of the Bacteria) consists of pure or altered cellulose, sometimes forming a gelatinous covering, at other times a harder one, with deposits of chalk or silica formed in it. The cell-nucleus, which in the Schizophyta is less differentiated, may be one or more (e.g. Hydrodictyon, Siphoneæ) in each cell. Excepting in the majority of the Bacteria, colour materials (of which chlorophyll, or modifications of it, always seems to be found) occur, which either permeate the whole cytoplasm surrounding the cell-nucleus, as in most of the coloured Schizophyta, or are contained in certain specially formed small portions of protoplasm (chromatophores).

The individual at a certain stage of development consists nearly always of only one cell; by its division multicellular individuals may arise, or, if the daughter-cells separate immediately after the division, as in many of the simplest forms, the individual will, during the whole course of its existence, consist of only a single cell (unicellular Algæ). In multicellular individuals the cells may be more or less firmly connected, and all the cells of the individual may be exactly alike, or a division of labour may take place, so that certain cells undertake certain functions, and are constructed accordingly; this may also occur in parts of the cell in the large unicellular and multinuclear Algæ (Siphoneæ, p. 62).

The cells in most of the Algæ belong to the parenchymatous form; these, however, in the course of their growth, may very often become somewhat oblong; in many Algæ (particularly Fucoideæ and Florideæ) occur, moreover, hyphæ-like threads, which are very long, often branched, and are either formed of a single cell, or, more frequently, of a row of cells, having a well-pronounced apical growth. The parenchymatous as well as the hyphæ-like cells may, in the higher Algæ (especially in certain Fucoideæ and Florideæ), be further differentiated, so that they form well-defined anatomico-physiological systems of tissue, i.e. assimilating, conducting, storing, and mechanical.

With regard to the external form, the thallus may present no differentiation, as in many unicellular Algæ, or in multicellular Algæ of the lower order, which are then either equally developed in all directions (e.g. Pleurococcus, Fig. 47), or form flat cell-plates (Merismopedium) or threads (Oscillaria, Fig. 21). The first step in the way of differentiation appears as a difference between apex and base (Rivularia, Porphyra); but the division of labour may proceed so that differences may arise between vegetative and reproductive cells (Œdogonium, Fig. 54); hairs and organs of attachment (rhizoids and haptera), which biologically serve as roots, are developed, and even leaves in certain forms of high order, belonging to different classes (e.g. Caulerpa, Fig. 59; Characeæ, Fig. 61; Sargassum, Fig. 72; and many Florideæ).

=The non-sexual reproduction= takes place vegetatively, in many instances, simply by division into two, and more or less complete separation of the divisional products (Diatomaceæ, Desmidiaceæ (Fig. 36), many Fission-plants, etc.), or by detached portions of the thallus (e.g. Caulerpa, Ulva lactuca, etc.; among many Schizophyceæ, small filaments known as hormogonia are set free), or asexually by special reproductive cells (spores) set free from the thallus; these may be either stationary or motile. The stationary reproductive cells (spores) may either be devoid of cell-wall (tetraspores of the Florideæ), or may possess a cell-wall; in the latter case they may be formed directly from the vegetative cells, generally by the thickening of the walls (akinetes), or only after a process of re-juvenescence (aplanospores). Aplanospores, as well as akinetes, may either germinate immediately or may become resting-cells, which germinate only after a period of rest.

THE MOTILE ASEXUAL REPRODUCTIVE CELLS are spherical, egg- or pear-shaped, naked, swarmspores (zoospores), which have arisen in other cells (zoosporangia), and propel themselves through the water by means of cilia; or they are Phyto-Amœbæ, which have no cilia and creep on a substratum by means of pseudopodia. The cilia, which are formed from the protoplasm (in the Bacteria, however, from the membrane), are mostly situated at the pointed and colourless end, which is directed forwards when in motion, and are 1, 2 (Fig. 5 B), 4 or more. Both the cilia in the Brown Algæ are attached to one side (Fig. 65); they are occasionally situated in a circle round the front end (Œdogonium, Fig. 6 a, and Derbesia), or are very numerous and situated in pairs distributed over a large part or nearly the whole of the zoospore (Vaucheria). Besides being provided with one or more nuclei (Vaucheria), they may also have a red “eye spot” and vacuoles, which are sometimes pulsating, i.e. they appear and reappear at certain intervals. The swarmspores move about in the water in irregular paths, and apparently quite voluntarily, revolving round their longer axes; but they come to the surface of the water in great numbers either because of their dependence on light, or driven by warm currents in the water, or attracted by some passing mass of food material. The swarmspores germinate, each forming a new plant, as their movement ceases they surround themselves with a cell-wall, grow, and then divide; in Fig. 6 b, two may be seen in the condition of germination, and about to attach themselves by means of the front end, which has been developed into haptera (see also Fig. 5 B, lowest figure).

=The sexual reproduction= here, probably in all cases, consists in the coalescence of two masses of protoplasm, that is, in the fusion of their nuclei.

The simplest and lowest form is termed =conjugation=, or =isogamous= fertilisation, and is characterized by the fact that the two coalescing cells (termed gametes) are equal, or almost equal, in shape and size (the female gamete in the Cutleriaceæ, e.g. Zanardinia collaris, Fig. 7, is considerably larger than the male gamete). The cell in which the gametes are developed is called a gametaugium, and the reproductive cell formed by their union--which generally has a thick wall and only germinates after a short period of rest--is termed a zygote or zygospore. The conjugation takes place in two ways:--

(a) In the one way the gametes are motile cells (planogametes, zoogametes, Fig. 8), which unite in pairs during their swarming hither and thither in the water; during this process they lie side by side (Fig. 8 d), generally at first touching at the clear anterior end, and after a time they coalesce and become a motionless zygote, which surrounds itself with a cell-wall (Fig. 8 e). This form of conjugation is found in Ulothrix (Fig. 8 d), Acetabularia, and other Algæ (Figs. 45, 56, 66).

(b) Among other Algæ (e.g. Diatomaceæ and Conjugatæ), the conjugating cells continue to be surrounded by the cell-wall of the mother-cell (aplanogametes in an aplanogametangium); the aplanogametangia generally grow out into short branches, which lie close together and touch one another, the wall at the point of contact is then dissolved (Fig. 39). Through the aperture thus formed, the aplanogametes unite, as in the first instance, and form a rounded zygote, which immediately surrounds itself with a cell-wall. Various modifications occur; compare Figs. 37, 39, 41, 43.

The highest form of the sexual reproduction is the =Egg- or Oogamous= fertilisation. The two coalescing cells are in the main unlike each other in form as well as size. The one which is considered as the male, and is known as the spermatozoid (antherozoid), developes as a rule in large numbers in each mother-cell (antheridium); they are often self-motile (except in the Florideæ, where they are named spermatia), and are many times smaller than the other kind, the female, which is known as the egg-cell, (oosphere). The egg-cell is always a motionless, spherical, primordial cell which can either float about freely in the water, as in the Fucaceæ (Fig. 9), or is surrounded by a cell-wall (oogonium); generally only one oosphere is to be found in each oogonium, but several occur in Sphæroplea (Fig. 10). The result of the spermatozoid coalescing with the egg-cell is, as in this case, the formation of a oospore, which generally undergoes a period of rest before germination (the Florideæ are an exception, a fruit-body, cystocarp, being produced as the result of coalescence).

An example of fertilisation is afforded by the Alga, Sphæroplea annulina (Fig. 10). The filamentous thallus is formed of cylindrical cells with many vacuoles (r in A); some cells develope egg-cells (B), others spermatozoids (C), the latter in a particularly large number. The egg-cells are spherical, the spermatozoids of a club- or elongated pear-shape with two cilia at the front end (G; E is however a swarmspore). The spermatozoids escape from their cells through apertures in the wall (o in C) and enter through similar apertures (o in B) to the egg-cells. The colourless front end of the spermatozoid is united at first with the “receptive spot” of the egg-cell (see F), and afterwards completely coalesces with it. The result is the formation of a oospore with wart-like excrescences (D).

The female (parthenogenesis) or male (androgenesis) sexual cell may, sometimes without any preceding fertilisation, form a new individual (e.g. Ulothrix zonata, Cylindrocapsa, etc.).

=Systematic division of the Algæ.= The Algæ are divided into the following ten classes:

1. SYNGENETICÆ; 2. DINOFLAGELLATA, or PERIDINEA; 3. DIATOMACEÆ; 4. SCHIZOPHYTA, FISSION-ALGÆ; 5. CONJUGATÆ; 6. CHLOROPHYCEÆ, GREEN-ALGÆ; 7. CHARACEÆ, STONE-WORTS; 8. PHÆOPHYCEÆ; 9. DICTYOTALES; 10. RHODOPHYCEÆ.

Among the lowest forms of the Algæ, the Syngeneticæ, the Dinoflagellata, and the unicellular Volvocaceæ (Chlamydomoneæ), distinct transitional forms are found approaching the animal kingdom, which can be grouped as animals or plants according to their method of taking food or other characteristics. Only an artificial boundary can therefore be drawn between the animal and vegetable kingdoms. In the following pages only those forms which possess chromatophores, and have no mouth, will be considered as Algæ.

Class 1. =Syngeneticæ.=

The individuals are uni- or multicellular, free-swimming or motionless. The cells (which in the multicellular forms are loosely connected together, often only by mucilaginous envelopes) are naked or surrounded by a mucilaginous cell-wall, in which silica is never embedded. They contain one cell-nucleus, one or more pulsating vacuoles, and one to two band- or plate-like chromatophores with a brown or yellow colour, and sometimes a pyrenoid.

Reproduction takes place by vegetative division, or asexually by zoospores, akinetes (or aplanospores?). Sexual reproduction is unknown. They are all fresh water forms.

To this class may perhaps be assigned the recently arranged and very little known orders of Calcocytaceæ, Murracytaceæ, Xanthellaceæ, and Dictyochaceæ, which partly occur in the free condition in the sea, in the so-called “Plankton,” and partly symbiotic in various lower marine animals.

The Syngeneticæ are closely related to certain forms in the animal kingdom, as the Flagellatæ.

Order 1. =Chrysomonadinaceæ.= Individuals, uni- or multicellular, swimming in free condition, naked or surrounded by a mucilaginous covering. The cells are generally oval or elongated, with 2 (rarely only 1) cilia, almost of the same length, and generally with a red “eye-spot” at their base, and with 2 (rarely 1 only) band-shaped chromatophores. Reproduction by the longitudinal division of the individual cells either during the swarming, or during a resting stage; in the multicellular forms also by the liberation of one or more cells, which in the latter case are connected together.

A. Unicellular: Chromulina, Cryptoglena, Microglena, Nephroselmis.

B. Multicellular: Uroglena, Syncrypta (Fig. 11), Synura.

Among the unicellular Chrysomonadinaceæ are probably classed some forms which are only stages in the development of the multicellular, or of other Syngeneticæ.

Order 2. =Chrysopyxaceæ= are unicellular, and differ mainly from the preceding in being attached either on a slime-thread (Stylochrysalis), or enclosed in an envelope (Chrysopyxis, Fig. 12). They have two cilia, and multiply by longitudinal (Chrysopyxis) or transverse division, and the swarming of one of the daughter-individuals (zoospore). Division may also take place in a motionless stage (palmella-stage).

Order 3. =Dinobryinaceæ.= The individuals are originally attached, uni- or multicellular; each individual cell is distinctly contractile, and fixed at the bottom of a cup-shaped, open envelope. Cilia 2, but of unequal length. Asexual reproduction by zoospores, which are formed by straight or oblique longitudinal division of the mother-cell, during a palmella-stage which is produced in the winter aplanospores. Epipyxis, Dinobryon.

Order 4. =Hydruraceæ.= The individuals are attached, without cilia, multicellular, branched, and with apical growth. The cells are spherical, but in the final stage almost spindle-shaped, and embedded in large masses of mucilage. Asexual reproduction by zoospores which are tetrahedric, with 1 cilia, and by resting akinetes. Hydrurus is most common in mountain brooks.

Class 2. =Dinoflagellata.=

The individuals are of a very variable form, but always unicellular, and floating about in free condition. The cell is dorsiventral, bilateral, asymmetric and generally surrounded by a colourless membrane, which has no silica embedded in it, but is formed of a substance allied to cellulose. The membrane, which externally is provided with pores and raised borders, easily breaks up into irregularly-shaped pieces. In the forms which have longitudinal and cross furrows, two cilia are fixed where these cross each other, and project through a cleft in the membrane; one of these cilia projects freely and is directed longitudinally to the front or to the rear, the other one stretches crosswise and lies close to the cell, often in a furrow (cross furrow). The chromatophores are coloured brown or green and may either be two parallel (Exuviella), or several radially placed, discs, which sometimes may coalesce and become a star-shaped chromatophore. The coloring material (pyrrophyl) consists, in addition to a modification of chlorophyl, also of phycopyrrin and peridinin; this colour is sometimes more or less masked by the products of assimilation which consist of yellow, red or colourless oil (?) and starch. Cell-nucleus one: in Polydinida several nuclei are found; contractile vacuoles many, which partly open in the cilia-cleft (Fig. 13 gs). In some an eye-spot, coloured red by hæmatochrome, is found. Pyrenoids occur perhaps in Exuviella and Amphidinium.

THE REPRODUCTION takes place as far as is known at present, only by division. This, in many salt water forms, may take place in the swarming condition, and, in that case, is always parallel to the longitudinal axis. The daughter-individuals, each of which retains half of the original shell, sometimes do not separate at once from each other, and thus chains (e.g. in Ceratium) of several connected individuals may be formed. In others, the division occurs after the cilia have been thrown off and the cell-contents rounded. The daughter-cells then adopt entirely new cell-walls. A palmella-stage (motionless division-stage) sometimes appears to take place, and also aplanospores (?) with one or two horn-like elongations (e.g. in Peridinium cinctum and P. tabulatum); at germination one, or after division, two or more, new individuals may be formed.

Sexual reproduction has not been observed with certainty.

The Dinoflagellata move forward or backward, turning round their longitudinal axes; in their motion they are influenced by the action of light. The motion possibly may be produced only by the transverse cilium, which vibrates rapidly; whilst the longitudinal cilium moves slowly, and is supposed to serve mainly as a steering apparatus. They live principally in salt water, but also in fresh.

Besides the coloured forms, which are able to make their own organic compounds by the splitting up of the carbonic acid contained in the water, there are a few colourless forms (e.g. Gymnodinium spirale), or such as do not possess chromatophores (Polykrikos); these appear to live saprophytically, and may be able to absorb solid bodies with which they come in contact.

Dinoflagellata occur in the “Plankton” of the open sea, where they form together with Diatomaceæ the basis for the animal life. It is known with certainty that some salt water forms (like the Noctiluca, which belongs to the animal kingdom and to which they are perhaps related) produce light, known as phosphorescence.

Dinoflagellata (Peridinea, Cilioflagellata) are allied through their lowest form (Exuviella) to the Syngeneticæ and especially to the order Chrysomonadinaceæ. They may be divided into three orders.

Order 1. =Adinida.= Without transverse or longitudinal furrows, but enclosed in two shells, and with two parallel chromatophores in each cell. Exuviella, Prorocentrum.

Order 2. =Dinifera.= With tranverse and generally longitudinal furrow. Many radially-placed, disc-formed chromatophores. The most common genera are--Ceratium (Fig. 13), Peridinium, Glenodinium (Fig. 13), Gymnodinium, Dinophysis.

Order 3. =Polydinida.= With several transverse furrows, no chromatophores, and several cell-nuclei. Only one genus--Polykrikos.

The order Polydinida deviates in a high degree from the other Dinoflagellata, not only by its many tranverse furrows, each with its own transverse cilium, and by the absence of chromatophores, but also in having several cell-nuclei and a kind of stinging capsule, which otherwise does not occur within the whole class. It may therefore be questionable whether this order should really be placed in the vegetable kingdom.

Class 3. =Diatomeæ.=

The individuals--each known as a frustule--assume very various forms and may be unicellular or multicellular, but present no differentiation; many similar cells may be connected in chains, embedded in mucilaginous masses, or attached to mucilaginous stalks. The cells are bilateral or centric, often asymmetrical, slightly dorsiventral and have no cilia; those living in the free condition have the power of sliding upon a firm substratum. The cell contains 1 cell-nucleus and 1–2 plate-shaped or several disc-shaped chromatophores. The colouring material “Melinophyl” contains, in addition to a modification of chlorophyl, a brown colouring matter, diatomin. 1 or 2 pyrenoids sometimes occur. Starch is wanting and the first product of assimilation appears to be a kind of oil (?).

The cell-walls are impregnated with silica to such a degree that they are imperishable and are therefore able to contribute in a great measure to the formation of the earth’s crust. The structure of their cell-wall is most peculiar and differs from all other plants (except certain Desmidiaceæ); it does not consist of a single piece but is made up of two--the “shells”--(compare Exuviella and Prorocentrum among the Dinoflagellata) which are fitted into each other, one being a little larger than the other and embracing its edge, like a box with its lid (Fig. 14 B). The two parts which correspond to the bottom and lid of the box are known as valves. Along the central line of the valves a longitudinal rib may often be found, interrupted at its centre by a small cleft (perhaps homologous with the cilia-cleft of the Dinoflagellata), through which the protoplasm is enabled to communicate with the exterior (Fig. 14 A). It is principally by reason of the valves, which bear numerous fine, transverse ribs, striæ or warts, etc. (Figs. 14, 15, 17), that the Diatomeæ have become so well known and employed as test objects in microscopical science. When the division takes place, the two shells are separated a little from each other, and after the cell-contents have divided into two masses, two new shells are formed, one fitting into the larger valve, the other one into the smaller valve of the original frustule. The latter cell (frustule) is thus, upon the whole, smaller than the mother-cell, and as the cells do not increase in size, some frustules are smaller than the ones from which they are derived, and thus, by repeated divisions, it follows that smaller and smaller frustules are produced. This continued diminution in size is, however, compensated for by the formation, when the cells have been reduced to a certain minimum, of auxospores, 2–3 times larger. These may either be formed asexually by the protoplasm of a cell increasing, rounding off and surrounding itself with a new wall (e.g. Melosira) or after conjugation, which may take place with various modifications: 1. Two individuals unite after the secretion of a quantity of mucilage, and the valves then commence to separate from each other, on the side which the two individuals turn towards each other. The protoplasmic bodies now release themselves from their cell-wall, and each rounds off to form an ellipsoidal mass; these two protoplasmic masses (gametes) coalesce to form a zygote, the cell-nuclei and chromatophores also fusing together. The zygote increases in size, and surrounds itself with a firm, smooth, siliceous wall--the perizonium. The auxospores, whichever way they arise, are not resting stages. The germination of the zygote commences by the protoplasm withdrawing itself slightly from the cell-wall and constructing first the larger valve, and later on the smaller one; finally the membrane of the zygote bursts (e.g. Himantidium). 2. The conjugation occurs in a similar manner, but the protoplasm of the cells divides transversely before conjugation into two daughter-cells. Those lying opposite one another conjugate (Fig. 16) and form two zygotes. The formation of the perizonium, and germination take place as in the preceding instance (e.g. Epithemia). 3. Two cells place themselves parallel to each other, and each of the two cell-contents, without coalescing, becomes an auxospore. The formation of the wall takes place as in the preceding case. This is found in the Naviculeæ, Cymbelleæ, the Gomphonemeæ (e.g. Frustulia, Cocconema).

The Diatomaceæ may be found in salt as well as in fresh water (often in such masses that the colour of the water or mud becomes yellow or brown; in the same manner the genera Chætoceros, Rhizosolenia, Coscinodiscus, and several others, form large slime-masses, “Plankton” on the surface of the sea), on damp soil and in dust blown by the wind. They occur as fossils in the recent formations, often in large deposits (siliceous earth, mountain meal), as in the cement lime in Jutland, the alluvial deposits beneath Berlin, in clay strata beneath peat bogs, in guano, etc. These accumulations of fossilized diatoms are used in the manufacture of dynamite and in various manufactures.

The Diatomaceæ appear nearest to, and must be placed as a group co-ordinate with the Dinoflagellata, as they doubtless may be supposed to derive their origin from forms resembling Exuviella, and to have lost the cilia. The resemblances to the Desmidiaceæ which are striking in many respects, can only be conceived as analogies, and cannot be founded upon homologies, and it is therefore impossible to regard them as proof of genetic relationship. The family contains only one order.

Order 1. =Diatomaceæ.= This order may be divided into two sub-orders, viz.--

Sub-Order 1. =Placochromaticæ.= The chromatophores are discoid, large, 1 or 2 in each cell; the structure of the valves is bilateral and always without reticulate markings. The following groups belong to this sub-order: Gomphonemeæ, Cymbelleæ, Amphoreæ, Achnantheæ, Cocconeideæ, Naviculeæ, Amphipleureæ, Plagiotropideæ, Amphitropideæ, Nitzchieæ, Surirayeæ, and Eunotieæ.

Sub-Order 2. =Coccochromaticæ.= The chromatophores are granular, small and many in each cell. The structure of the cells is zygomorphic or centric, often with reticulate markings. The following groups belong to this sub-order: Fragilarieæ, Meridieæ, Tabellarieæ, Licmophoreæ, Biddulphieæ, Anguliferæ, Eupodisceæ, Coscinodisceæ, and Melosireæ.

Class 4. =Schizophyta, Fission-Algæ.=

The individuals are 1--many celled; the thallus consists in many of a single cell, in others of chains of cells, the cells dividing in only one definite direction (Figs. 18, 21). In certain Fission-Algæ the cell-chain branches (Fig. 30) and a difference between the anterior and the posterior ends of the chain is marked; in some, the cells may be united into the form of flat plates by the cell-division taking place in two directions; and in others into somewhat cubical masses, or rounded lumps of a less decided form, by the divisions taking place in three directions; or less defined masses may be formed by the divisions taking place in all possible directions.

The cell-walls rarely contain cellulose, they often swell considerably (Figs. 20, 22), and show distinct stratifications, or they are almost completely changed into a mucilaginous mass in which the protoplasts are embedded, e.g. in Nostoc (Fig. 22), and in the “Zooglœa” stage of the Bacteria (Fig. 27). Sexual reproduction is wanting. Vegetative reproduction by division and the separation of the divisional products by the splitting of the cell-wall or its becoming mucilaginous; among the Nostocaceæ, Lyngbyaceæ, Scytonemaceæ, etc., “Hormogonia” are found; in Chamæsiphon and others single reproductive akinetes are formed. Many Fission-Algæ conclude the growing period by the formation of resting akinetes or aplanospores.

The Schizophyta may be divided into 2 families:

1. SCHIZOPHYCEÆ.

2. BACTERIA.

Family 1. =Schizophyceæ,[5] Blue-Green Algæ.=

All the Blue-green Algæ are able to assimilate carbon by means of a colouring material containing chlorophyll (cyanophyll); but the chlorophyll in this substance is masked by a blue (phycocyan), or red (phycoerythrin, e.g. in Trichodesmium erythræum in the Red Sea) colouring matter which may be extracted from them in cold water after death. The colouring matter, in most of them, permeates the whole of the protoplasm (excepting the cell-nucleus), but in a few (e.g. Glaucocystis, Phragmonema), slightly developed chromatophores are to be found. Where the cells are united into filaments (cell-chains) a differentiation into apex and base (Rivulariaceæ) may take place, and also between ordinary vegetative cells and heterocysts; these latter cannot divide, and are distinguished from the ordinary vegetative cells (Fig. 22 h) by their larger size, yellow colour, and poverty of contents. Branching sometimes occurs and is either true or spurious.

The cell-chain in the spurious branching divides into two parts, of which either one or both grow beyond the place of division (Fig. 18) and often out to both sides (e.g. Scytonema), the divisions however, always take place transversely to the longitudinal direction of the cell-chain. In the true branching a cell elongates in the direction transverse to the cell-chain, and the division then takes place nearly at right angles to the former direction (Sirosiphoniaceæ).

Cilia are wanting, but the filaments are sometimes self-motile (e.g. hormogonia in Nostoc) and many partly turn round their axes, partly slide forward or backward (Oscillaria).

Reproduction takes place by spores and hormogonia in addition to simple cell-division. Hormogonia are peculiar fragments of a cell-chain capable of motion, and often exhibit a vigorous motion in the sheath, until at last they escape and grow into a new individual (Fig. 18). The spores are reproductive akinetes (Chamæsiphon, etc.) or resting akinetes; these latter arise by the vegetative cells enlarging and constructing a thick cell-wall (Fig. 19 e f). On germination, this cell-wall bursts and the new cell-chain elongates in the same longitudinal direction as before (Fig. 19 b c). Many (e.g. Oscillaria) may however winter in their ordinary vegetative stage. Aplanospores are wanting.

The Fission-Algæ are very prevalent in fresh water and on damp soil, less so in salt water; they also often occur in water which abounds in decaying matter. Some are found in warm springs with a temperature as high as 50° C.

The Family may be divided into 2 sub-families:

1. HOMOCYSTEÆ (heterocysts are wanting): Chroococcaceæ, Lyngbyaceæ and Chamœsiphonaceæ.

2. HETEROCYSTEÆ (heterocysts present): Nostocaceæ, Rivulariaceæ, Scytonemaceæ and Sirosiphoniaceæ.

Order 1. =Chroococcaceæ.= The individuals are 1--many-celled, but all the cells are uniform, united to form plates or irregular masses, often surrounded by a mucilaginous cell-wall, but never forming cell-chains. Multiplication by division and sometimes by resting akinetes, but reproductive akinetes are wanting. Chroococcus, Aphanocapsa, Glœocapsa (Fig. 20), Cœlosphærium, Merismopedium, Glaucocystis, Oncobyrsa, Polycystis, Gomphosphæria.

Order 2. =Lyngbyaceæ (Oscillariaceæ).= The cells are discoid (Fig. 21), united to straight or spirally twisted, free filaments, which are unbranched, or with spurious branching. The ends of the cell-chains are similar. Heterocysts absent. Reproduction by synakinetes, resting akinetes are wanting. Oscillaria (Fig. 21), Spirulina, Lyngbya, Microcoleus, Symploca, Plectonema.

Order 3. =Chamæsiphonaceæ.= The individuals are 1--many-celled, attached, unbranched filaments with differentiation into apex and base, without heterocysts. Multiplication by reproductive akinetes; resting akinetes are wanting. Dermocarpa, Clastidium, Chamæsiphon, Godlewskia, Phragmonema.

Order 4. =Nostocaceæ.= The individuals are formed of multicellular, unbranched filaments, without differentiation into apex and base; heterocysts present. Reproduction by synakinetes and resting akinetes.

Some genera are not mucilaginous, e.g. Cylindrospermum (Fig. 19). The cell-chains in others, e.g. Nostoc, wind in between one another and are embedded in large structureless jelly-like masses, which may attain the size of a plum or even larger (Fig. 22); sometimes they are found floating in the water, sometimes attached to other bodies. Other genera as follows: Aphanizomenon and Anabæna (in lakes and smaller pieces of water); Nodularia is partly pelagic. Some occur in the intercellular spaces of higher plants, thus Nostoc-forms are found in Anthoceros, Blasia, Sphagnum, Lemna, and in the roots of Cycas and Gunnera; Anabæna in Azolla.

Order 5. =Rivulariaceæ.= The individuals are multicellular filaments, with differentiation into apex and base; spurious branching, and a heterocyst at the base of each filament, reproduction by synakinetes and resting akinetes, rarely by simple reproductive akinetes. Rivularia, Glœotrichia, Isactis, Calothrix.

Order 6. =Scytonemaceæ.= The individuals are formed of multicellular filaments with no longitudinal division; differentiation into apex and base very slight or altogether absent; branching spurious; heterocysts present. Reproduction by synakinetes, rarely by resting akinetes and ordinary reproductive akinetes. Tolypothrix, Scytonema, Hassalia, Microchæte.

Order 7. =Sirosiphoniaceæ.= The individuals are formed of multicellular threads with longitudinal divisions; true branching and heterocysts, and often distinct differentiation into apex and base. Reproduction by synakinetes, rarely by resting akinetes and ordinary reproductive akinetes. Hapalosiphon, Stigonema, Capsosira, Nostocopsis, Mastigocoleus.

Family 2. =Bacteria.=[6]

The Bacteria (also known as Schizomycetes, and Fission-Fungi) are the smallest known organisms, and form a parallel group to the Blue-green Algæ, but separated from these Algæ by the absence of their colouring material; chlorophyll is only found in a few Bacteria.

The various forms under which the vegetative condition of the Bacteria appear, are termed as follows:

1. GLOBULAR FORMS, COCCI (Figs. 27, 30 c): spherical or ellipsoidal, single cells, which, however, are usually loosely massed together and generally termed “Micrococci.”

2. ROD-LIKE FORMS: more or less elongated bodies; the shorter forms have been styled “Bacterium” (in the narrower sense of the word), and the term “Bacillus” has been applied to longer forms which are straight and cylindrical (Figs. 28, 29, 30 E).

3. THREAD-LIKE FORMS: unbranched, long, round filaments, resembling those of Oscillaria, are possessed by Leptothrix (very thin, non-granular filaments; Fig. 30 A, the small filaments) and Beggiatoa (thicker filaments, with strong, refractile grains or drops of sulphur (Fig. 31); often self-motile). Branched filaments, with false branching like many Scytonemaceæ, are found in Cladothrix (Fig. 30 B, G).

4. SPIRAL FORMS: Rod-like or filamentous bodies, which more or less strongly resemble a corkscrew with a spiral rising to the left. In general these are termed Spirilla (Fig. 23); very attenuated spirals, Vibriones (standing next to Fig. 30 M); if the filaments are slender and flexible with a closely wound spiral, Spirochætæ (Fig. 24).

5. The MERISMOPEDIUM-FORM, consisting of rounded cells arranged in one plane, generally in groups of four, and produced by divisions perpendicular to each other.

6. The SARCINA-FORM, consisting of roundish cells which are produced by cellular division in all the three directions of space, united into globular or ovoid masses (“parcels”) e.g. Sarcina ventriculi (Figs. 25, 26).

All Bacteria are unicellular. In the case of the micrococci this is self-evident, but in the “rod,” “thread,” and “spiral” Bacteria, very often numerous cells remain united together and their individual elements can only be recognised by the use of special reagents.

The condition termed “Zooglœa,” which reminds us of Nostoc, is produced by the cells becoming strongly mucilaginous. A number of individuals in active division are found embedded in a mass of mucilage, which either contains only one, or sometimes more, of the above-named forms. The individuals may eventually swarm out and continue their development in an isolated condition. Such mucilaginous masses occur especially upon moist vegetables (potatoes, etc.), on the surface of fluids with decaying raw or cooked materials, etc. The mucilaginous envelope is thrown into folds when the Bacteria, with their mucilaginous cell-walls, multiply so rapidly that there is no more room on the surface of the fluid.

The cells of the Bacteria are constructed like other plant-cells in so far as their diminutive size has allowed us to observe them. The cell-wall only exceptionally shows the reactions of cellulose (in Sarcina, Leuconostoc; also in a Vinegar-bacterium, Bacterium xylinum); a mucilaginous external layer is always present. The body of the cell mostly appears to be an uniform or finely granulated protoplasm. Very few species (e.g. Bacillus virens) contain chlorophyll; others are coloured red (purple sulphur Bacteria); the majority are colourless. Bacillus amylobacter shows a reaction of a starch-like material when treated with iodine before the spore-formation. Some Bacteria contain sulphur (see p. 37). The body, which has been described as a cell-nucleus, is still of a doubtful nature.

Artificial colourings with aniline dyes (especially methyl-violet, gentian-violet, methylene-blue, fuchsin, Bismarck-brown and Vesuvin) play an important part in the investigations of Bacteria.

MOVEMENT. Many Bacteria are self-motile; the long filaments of Beggiatoa exhibit movements resembling those of Oscillaria. In many motile forms the presence of cilia or flagella has been proved by the use of stains; many forms have one, others several cilia attached at one or both ends (Fig. 23) or distributed irregularly over the whole body; the cilia are apparently elongations of the mucilaginous covering and not, as in the other Algæ of the protoplasm. In Spirochæte the movement is produced by the flexibility of the cell itself. Generally speaking, the motion resembles that of swarm-cells (i.e. rotation round the long axis and movement in irregular paths); but either end has an equal power of proceeding forwards.

The swarming motion must not be confounded with the hopping motion of the very minute particles under the microscope (Brownian movement).

VEGETATIVE REPRODUCTION takes place by continued transverse division; hence the name “Fission-Fungi” or “Fission-Algæ,” has been applied to the Bacteria.

SPORES. The spores are probably developed in two ways. In the ENDOSPOROUS species (Figs. 28, 29), the spore arises as a new cell inside the mother-cell. The spores are strongly refractile, smaller than the mother-cell, and may be compared to the aplanospores of other Algæ. In addition to these there are the ARTHROSPOROUS species in which the cells, just as in Nostoc and other Blue-green Algæ, assume the properties of spores without previously undergoing an endogenous new construction, and are able to germinate and form new vegetative generations (Fig. 27). The formation of spores very often commences when the vegetative development begins to be restricted.

The spores germinate as in Nostoc by the bursting of the external layer of the cell-wall, either by a transverse or longitudinal cleft, but always in the same way, in the same species (Fig. 28, example of transverse cleft).

DISTRIBUTION. Bacteria and their germs capable of development, are found everywhere, in the air (dust), in surface water, and in the superficial layers of the soil. The number varies very much in accordance with the nature of the place, season, etc. They enter, together with air and food, into healthy animals and occur always in their alimentary tract.

GROWTH AND REPRODUCTION depend upon the conditions of temperature. There is a certain minimum, optimum and maximum for each species; for instance (in degrees Centigrade)--

Minim. Opt. Maxim. Bacillus subtilis + 6 c. 30 + 50 B. anthracis 15 20–25 43 Spirillum choleræ asiaticæ 8 37 40 (but grows only feebly if under 16°). Bacterium tuberculosis 28 37–38 42

The functions of life cease on a slight excess of the maximum or minimum temperature, numbness setting in when either of these limits is passed. Crenothrix-threads provided with mucilaginous envelopes may, according to Zopf, sustain a temperature of-10°. Some Bacteria are said to be able to resist the exposure to as low a temperature as-110° for a short time. It is not known at what degree of cold the death of the Bacteria occurs: the greatest degree of heat which the vegetative cells can withstand is about the same as that for other vegetative plant-cells, namely, about 50–60° C. Certain Bacteria, e.g. B. thermophilus, grow and thrive vigorously at 70° C. Many spores, on the contrary, are able to bear far higher temperatures (in several species a temperature for some duration of above 100°, those of Bacillus subtilis, for instance, can withstand for hours a temperature of 100° in nutrient solutions; the spores remain capable of development after exposure to a dry heat of 123° C.).

The Desiccation of the air, if prolonged, kills many forms when in the vegetative condition. The spores however can bear a much longer period of dryness, some even several years.

OXYGEN. Some species cannot live without a supply of free oxygen (Aerobic), e.g. the Vinegar-bacteria, the Hay-bacilli, the Anthrax-bacilli, the Cholera-Microspira. Other species again thrive vigorously without supply of free oxygen, and are even checked in their development by the admission of air (Anaerobic), e.g. the butyric acid Bacterium (Clostridium butyricium = Bacillus amylobacter). A distinction may be drawn between obligate and facultative aerobics and obligate and facultative anaerobics. Several Bacteria, producing fermentation, may grow without the aid of oxygen when they are living in a solution in which they can produce fermentation; but, if this is not the case, they can only grow when a supply of oxygen is available. A great number of the pathogenic Bacteria belong to the facultative anaerobics.

A luminous Bacterium (Bacillus phosphorescens) which in the presence of a supply of oxygen gives a bluish-white light, has been found in sea-water. Phosphorescent Bacteria have frequently been observed upon decaying sea-fish, as well as on the flesh of other animals; by transferring the Bacteria from cod fish to beef, etc., the latter may be made luminous.

Organic carbon compounds are indispensable for all Bacteria, (except, as it appears, for the nitrifying organisms), as they can only obtain the necessary supplies of carbon from this source. The supplies of nitrogen, which also they cannot do without, can be obtained equally as well from organic compounds as from inorganic salts, such as saltpetre or ammonia-compounds. The various “ash-constituents” are also essential for their nourishment.

While Moulds and Yeast-Fungi grow best in an acid substratum, the Bacteria, on the other hand, generally thrive best in a neutral or slightly alkaline one.

In sterilization, disinfection, and antisepsis, means are employed by which the Bacteria are killed, or checked in their development, for instance, by heat (ignition, cooking, hot vapours, hot air, etc.), or poisons (acids, corrosive sublimate). The process of preserving articles of food, in which they are boiled and then hermetically sealed, aims at destroying the Bacteria, or the spores of those which already may be present in them, and excluding all others.

As the Bacteria are unable to assimilate carbon from the carbonic acid of the air, but must obtain it from the carbon-compounds already in existence in the organic world, they are either saprophytes or parasites. Some are exclusively either the one or the other, obligate saprophytes or parasites. But there are transitional forms among them, some of which are at ordinary times saprophytes, but may, when occasion offers, complete their development wholly or partly as parasites--facultative parasites; others are generally parasitic, but may also pass certain stages of development as saprophytes--facultative saprophytes.

All chlorophyll-free organisms act in a transforming and disturbing manner on the organic compounds from which they obtain their nourishment, and while they themselves grow and multiply, they produce, each after its kind, compounds of a less degree of complexity, i.e. they produce fermentation, putrefaction, sometimes the formation of poisons, and in living beings often disease.

Those organisms which produce fermentation are called ferments; this word, however, is also employed for similar transformations in purely chemical materials (inorganic ferments or enzymes). Many organic (“living”) ferments, among which are Yeast-cells and Bacteria, give off during their development certain inorganic and soluble ferments (enzymes) which may produce other transformations without themselves being changed. Different organisms may produce in the same substratum different kinds of transformation; alcoholic fermentation may for instance be produced by different species of Fungi, but in different proportions, and the same species produces in different substrata, different transformations (e.g. the Vinegar-bacteria oxydize diluted alcohol to vinegar, and eventually to carbonic acid and water).

In the study of Bacteria it is absolutely necessary to sterilize the vessels employed in cultivation, the apparatus, and nutrient solutions, i.e. to free them from Bacteria germs and also to preserve the cultures from the intrusion of any foreign germs (“pure-cultures”). A firm, transparent, nutritive medium is frequently employed. This may be prepared by adding to the nutrient solutions (broth) either gelatine, or--when the Bacteria are to be cultivated at blood-heat--serum of sheep’s or calf’s blood, agar-agar or carragen; serum alone may in itself serve as a nutrient medium. The so-called “plate-cultures” are frequently employed, i.e. the germs are isolated by shaking them with the melted liquid nutrient gelatine, which is then spread on a glass plate and allowed to coagulate; when later on the individual germs grow into colonies, these remain separate in the solid substratum and it is easy to pursue their further development. Similar plate-cultures may also be cultivated in test-tubes and on microscopic slides. The slides and glass plates must be placed in “moist chambers” free from Bacteria. By sowing a few cells (if possible one) using a fine platinum wire, pure cultures for further investigation may be obtained.

In order to prove the relationship between pathogenic Bacteria and certain diseases, the experimental production of pathogenic Bacteria by the inoculation of Bacteria from pure cultures into healthy animals, is very important.

It has not so far been possible to establish a classification of the Bacteria, as the life-history of many species, has not yet been sufficiently investigated.[7] The opinions of botanists are at variance, in many cases, about the forms of growth of a particular kind. Some species are pleomorphic (many-formed) while others possess only one form.

The following Bacteria are =Saprophytes=:--

Cladothrix dichotoma is common in stagnant and running water which is impregnated with organic matter; the cell-chains have false branching. According to Zopf, Leptothrix ochracea is one of the forms of this species which, in water containing ferrous iron (e.g. as FeCO_{3}), regularly embeds ferric-oxide in its sheath by means of the activity of the protoplasm. Leptothrix ochracea and other Iron-bacteria, according to Winogradsky (1888), do not continue their growth in water free from protoxide of iron; while they multiply enormously in water which contains this salt of iron. The large masses of ochre-coloured slime, found in meadows, bogs, and lakes, are probably due to the activity of the Iron-bacteria.

Those forms which, according to Zopf’s views, represent the forms of development of Cladothrix dichotoma are placed together in Fig. 30. A represents a group of plants, seventy times magnified, attached to a Vaucheria. The largest one is branched like a tree, with branches of ordinary form; a specimen with spirally twisted branches is seen to the right of the figure, at the lower part some small Leptothrix-like forms. B shows the manner of branching and an incipient Coccus-formation. C a Coccus-mass whose exit from the sheath has been observed. D the same mass as C after the course of a day, the Cocci having turned into rods. E a group of Cocci in which some have developed into shorter or longer rods. F one of these rods before and after treatment with picric acid, which causes the chain-like structure to become apparent. G a portion of a plant with conspicuous sheath, two lateral branches are being formed. H part of a plant, whose cells have divided and form Cocci. The original form of the cells in which the Cocci are embedded may still be recognised. I. Leptothrix-filaments with conspicuous mucilaginous sheath, from which a series of rods is about to emerge; the rod near the bottom is dead, and has remained lying in the sheath. K part of a plant which is forming Cocci, those at the top are in the zooglœa-stage, at the base they are elongating to form rods and Leptothrix-filaments. L a portion of a branched Cladothrix, which divides into motile Bacillus-forms; the rays at the free ends indicate the currents which the cilia produce in the water. M a spirally-twisted, swarming filament, before and after division into halves. N part of a tree-like zooglœa with Cocci and short rods.--All of these spirilla, zooglœa, etc., which Zopf has connected with Clad. dichotoma, are according to Winogradsky, independent organisms.

Micrococcus ureæ produces urinal fermentation (transformation of urinal matter into ammonium carbonate); aerobic; round cells generally united to form bent chains or a zooglœa.--Several other kinds of Bacteria have the same action as this one: in damp soil containing ammonia-compounds, saltpetre-formations are produced by M. nitrificans and several different kinds of Bacteria.

Micrococcus prodigiosus is found on articles of food containing starch; “bleeding bread” is caused by this Bacterium, which has the power of forming a red pigment; it also occurs in milk, and produces lactic acid.

Leuconostoc mesenterioides is the frog-spawn Bacterium (Fig. 27) which is found in sugar manufactories, and has the power of producing a viscous fermentation in saccharine solutions which have been derived from plants, e.g. in beetroot-sugar manufactories, where large accumulations of mucilage are formed at the expense of the sugar, with an evolution of carbonic acid. The cell-rows, resembling somewhat a pearl necklace, have thick mucilaginous cell-walls, and form white “Nostoc”-lumps. The mucilage eventually deliquesces and the cells separate from each other; arthrospores?--Similar viscous deteriorations occur in beer and wine, which may then be drawn out into long, string like filaments--“ropiness.”

Bacterium aceti, the Vinegar-bacterium, oxidizes alcohol into acetic acid (acetous-fermentation) and forms a greyish covering of Bacteria (“Vinegar-mother”) on the surface of the liquid; the acetic acid formed, becomes by continued oxidization by B. aceti, again transformed into carbonic acid and water. Aerobic; short cylindrical cells, often united into chains, or to form a zooglœa; sometimes also rod-and spindle-shaped. The Vinegar-bacteria and other kinds with ball- or rod-forms sometimes become swollen, spindle-shaped, or oval links; they are supposed to be diseased forms[8] (“Involution-forms”).

Bacillus lacticus (Bacterium acidi lactici, Zopf) is always found in milk which has stood for some time, and in sour foods (cabbage, cucumbers, etc.); it turns the milk sour by producing lactic acid fermentation in the sugar contained in the milk; the lactic acid formed, eventually causes the coagulation of the casein. It resembles the Vinegar-bacteria, occurring as small cylindrical cells, rarely in short rows; not self-motile.--Several other Bacteria appear to act in the same way, some occurring in the mouth of human beings; some of these Bacteria give to butter its taste and flavour.

The kefir-grains which are added to milk for the preparation of kefir, contain in large numbers a Bacterium (Dispora caucasica) in the zooglœa-form, a Yeast-fungus, and Bacillus lacticus. Kefir is a somewhat alcoholic sour milk, rich in carbonic acid; it is a beverage manufactured by the inhabitants of the Caucasus, from the milk of cows, goats, or sheep, and is sometimes used as a medicine. In the production of kefir, lactic acid fermentation takes place in one part of the sugar contained in the milk, and alcoholic fermentation in another part, and the casein which had become curdled is partially liquefied (peptonised) by an enzyme of a Zooglœa-bacterium.

Bacillus amylobacter (Bacillus butyricus), the Butyric-acid-bacterium (Fig. 29), is a very common anaerobic which produces fermentation in sugar and lactic-acid salts, and whose principal product is butyric acid. It destroys articles of food and (together with other species) plays a part in the butyric acid fermentation which is necessary in the making of cheese; it is very active wherever portions of plants are decaying, in destroying the cellulose in the cell-walls of herbaceous plants, and is thus useful in the preparation of flax and hemp. The cells are self-motile, generally cylindrical, sometimes united into short rows; endosporous; the spore-forming cells swell, assume very different forms, and show granulose reaction. The germ-tube grows out in the direction of the long axis of the spore.

Bacillus subtilis, the Hay-bacillus, is developed in all decoctions of hay; a slender, aerobic, self-motile Bacillus; endosporous (aplanospores); the spore-wall ruptures transversely on germination.

Crenothrix kuehniana occurs in the springs of many baths, in wells, in water or drain-pipes.

Beggiatoa (parallel with the Blue-green Alga Oscillaria). Long filaments formed of cylindrical cells which are attached by one of the ends, but which are nearly always free when observed. The filaments, like those of Oscillaria, describe conical figures in their revolutions, the free filaments slide upwards and parallel with one another; sheaths are wanting; strongly refractive sulphur drops are found in the interior. The Beggiatoas are the most prevalent Sulphur-bacteria. They occur, very commonly in large numbers, wherever plant or animal remains are decaying in water in which sulphuretted hydrogen is being formed; thus, for example, B. alba (Fig. 31) occurs frequently as a white covering or slimy film on mud containing organic remains. ~B. mirabilis is remarkable for its size and its strong peristaltic movements.~ The Sulphur-bacteria oxidize the sulphuretted hydrogen, and accumulate sulphur in the shape of small granules of soft amorphic sulphur, which in the living cell never passes over into the crystalline state. They next oxidize this sulphur into sulphuric acid, which is immediately rendered neutral by absorbed salts of calcium, and is given off in the form of a sulphate, thus CaCO_{3} is principally changed into CaSO_{4}. In the absence of sulphur the nutritive processes are suspended, and consequently death occurs either sooner or later. The Sulphur-bacteria may exist and multiply in a fluid which only contains traces of organic matter, in which organisms devoid of chlorophyll are not able to exist. The Beggiatoas very frequently form white, bulky masses in sulphur wells and in salt water, the traces of organic material which the sulphur water contains proving sufficient for them. ~The cellulose-fermentation, to which the sulphur wells in all probability owe their origin, mainly procures them suitable conditions for existence. The CaCO_{3} and H_{2}S, formed during the cellulose fermentation by the reduction of CaSO_{4} is again changed into CaSO_{4} and CO_{2} by the Sulphur-bacteria (Winogradsky, 1887).--Other Sulphur-bacteria, the so-called purple Sulphur-bacteria, e.g. B. roseo-persicina, Spirillum sanguineum (Fig. 23), Bacterium sulfuratum, etc., have their protoplasm mixed with a red colouring matter (bacterio-purpurin) which, like chlorophyll, has the power, in the presence of light, of giving off oxygen (as proved by T. W. Englemann, 1888, in oxygen-sensitive Bacteria). The three purple Sulphur-bacteria mentioned, are, according to Winogradsky, not pleomorphic kinds but embrace numerous species.~

Many Spirilli (Spirillum tenue, S. undula, S. plicatile, and others) are found prevalent in decaying liquids.

Bacteria (especially Bacilli) are the cause of many substances emitting a foul odour, and of various changes in milk.

=Parasitic Bacteria= live in other living organisms; but the relation between “host” and parasite may vary in considerable degree. Some parasites do no injury to their host, others produce dangerous contagious diseases; some choose only a special kind as host, others again live equally well in many different ones. There are further specific and individual differences with regard to the predisposition of the host, and every individual has not the same receptivity at all times.

THE HARMLESS PARASITES OF HUMAN BEINGS. Several of the above mentioned saprophytes may also occur in the alimentary canal of human beings; e.g., the Hay-bacillus, the Butyric-acid-bacillus, etc.; but the gastric juice prevents the development of others, at all events in their vegetative condition. Sarcina ventriculi, “packet-bacterium,” is only known to occur in the stomach and intestines of human beings, and makes its appearance in certain diseases of the stomach (dilation of the stomach, etc.) in great numbers, without, however, being the cause of the disease. It occurs in somewhat cubical masses of roundish cells (Fig. 25).

LESS DANGEROUS PARASITES. In the mouth, especially between and on the teeth, a great many Bacteria are to be found (more than fifty species are known), e.g. Leptothrix buccalis (long, brittle, very thin filaments which are united into bundles), Micrococci in large lumps, Spirochæte cohnii, etc. Some of them are known to be injurious, as they contribute in various ways to the decay of the teeth (caries dentium); a Micrococcus, for instance, forms lactic acid in materials containing sugar and starch, and the acid dissolves the lime salts in the external layers of the teeth: those parts of the teeth thus deprived of lime are attacked by other Bacteria, and become dissolved. Inflammation in the tissues at the root of a tooth, is probably produced by septic materials which have been formed by Bacteria in the root-canal.

DANGEROUS PARASITES. In a large number of the infectious diseases of human beings and animals, it has been possible to prove that parasitic Bacteria have been the cause of the disease. Various pathogenic Bacteria of this nature, belonging to the coccus, rod, and spiral Bacteria groups, are mentioned in the following:--

=Pathogenic Micrococci.= Staphylococcus pyogenes aureus produces abscesses of various natures (boils, suppurative processes in internal organs). The same effects are produced by--

Streptococcus pyogenes, which is the most frequent cause of malignant puerperal fever; it is perhaps identical with--

Streptococcus erysipelatis, which is the cause of erysipelas in human beings.

Diplococcus pneumoniæ (A. Fränkel) is the cause of pneumonia, and of the epidemic cerebro-spinal meningitis.

Gonococcus (Neisser) is the cause of gonorrhea and inflammation of the eyes.

=Pathogenic Rod-Bacteria.= Bacterium choleræ gallinarum, an aerobic, facultative parasite which produces fowl-cholera among poultry; it is easily cultivated on various substrata as a saprophyte. The disease may be conveyed both through wounds and by food, and may also be communicated to mammals.

Bacillus anthracis, the Anthrax bacillus (Fig. 32), chiefly attacks mammals, especially herbivorous animals (house mice, guinea-pigs, rabbits, sheep, cattle), in a less degree omnivorous animals (including human beings), and in a still less degree the Carnivores. Aerobic. Cylindrical cells, 3–4 times as long as broad, united into long rod-like bodies, which may elongate into long, bent, and twisted filaments. Not self-motile. Endosporous. Germination takes place without the throwing off of any spore-membrane (compare Hay-bacillus p. 37 which resembles it). Contagion may take place both by introduction into wounds, and from the mucous membrane of the intestines or lungs, both by vegetative cells and by spores; in intestinal anthrax, however, only by spores. The Bacillus multiplies as soon as it has entered the blood, and the anthrax disease commences. The Bacilli not only give off poison, but also deprive the blood of its oxygen. Vegetative cells only occur in living animals. This species is a facultative parasite which in the first stage is a saprophyte, and only in this condition forms spores.

Bacillus tuberculosis produces tuberculosis in human beings, also in domestic animals (perlsucht). It is a distinct parasite, but may also live saprophytically. It is rod-formed, often slightly bent, and is recognised principally by its action with stains (when stained with an alkaline solution of methyl-blue or carbolic fuchsin, it retains the colour for a long time even in solutions of mineral acids, in contrast with the majority of well-known Bacteria): it probably forms spores which are able to resist heat, dryness, etc.

Bacillus lepræ produces leprosy; Bacillus mallei produces glanders; Bacillus tetani, tetanus (the tetanus bacillus is very common in soil; anaerobic); Bacillus diphtheriæ, diphtheria; Bacillus typhosus, typhoid fever, etc.

=Pathogenic Spiral Bacteria.= Spirochæte obermeieri (Fig. 24) produces intermittent fever (febris recurrens); it makes its appearance in the blood during the attacks of fever, but it is not to be found during intervals when there is no fever. Obligate parasite.

Spirillum choleræ asiaticæ (Microspira comma) without doubt produces Asiatic cholera; an exceedingly motile spirillum, which is also found in short, bent rods (known as the “Comma-bacillus”), it lives in the intestines of those attacked by the disease, and gives off a strong poison which enters the body. It is easily cultivated as a saprophyte.

A great many circumstances seem to show that a number of other infectious diseases (syphilis, small-pox, scarlet-fever, measles, yellow-fever, etc.) owe their origin to parasitic Bacteria, but this has not been proved with certainty in all cases.

It has been possible by means of special cultivations (ample supply of oxygen, high temperature, antiseptic materials) to produce from the parasitic Bacteria described above (e.g. the fowl-cholera and the anthrax Bacteria) physiological varieties which are distinct from those appearing in nature and possess a less degree of “virulence,” i.e. produce fever and less dangerous symptoms in those animals which are inoculated with them. The production of such physiological varieties has come to be of great practical importance from the fact that they are used as vaccines, i.e. these harmless species produce in the animals inoculated with them immunity from the malignant infectious Bacteria from which they were derived. This immunity is effected by the change of the products of one or more of the Bacteria, but we do not yet know anything about the way in which they act on the animal organism. The white blood corpuscles, according to the Metschnikoff, play the part of “Phagocytes” by absorbing and destroying the less virulent Bacteria which have entered the blood, and by so doing they are gradually enabled to overcome those of a more virulent nature.

Class 5. =Conjugatæ.=

The Algæ belonging to this class have chlorophyll, and pyrenoids round which starch is formed. The cells divide only in one direction, they live solitarily, or united to form filaments which generally float freely (seldom attached). Swarm-cells are wanting. The fertilisation is isogamous (conjugation) and takes place by means of aplanogametes. The zygote, after a period of rest, produces, immediately on germination, one or more new vegetative individuals; sometimes akinetes or aplanospores are formed in addition. They only occur in fresh or slightly brackish water.

Order 1. =Desmidiaceæ.= The cells generally present markings on the outer wall, and are mostly divided into two symmetrical halves by a constriction in the middle, or there is at least a symmetrical division of the protoplasmic cell-contents. The cell-wall consists nearly always of two layers, the one overlapping the other (Fig. 35 C). The cells either live solitarily or are united into unbranched filaments. The mass of protoplasm formed by the fusion of the two conjugating cells becomes the zygote, which on germination produces one (or after division 2, 4 or 8) new vegetative individual. The chromatophores are either star-, plate-, or band-shaped, and regularly arranged round the long axis of the cell.

The Desmidiaceæ are not able to swim independently, many species, however, show movements of different kinds by rising and sliding forward on the substratum. These movements, which are partly dependent upon, and partly independent of light and the force of gravitation, are connected with the protrusion of a mucilaginous stalk. The mucilage, which sometimes surrounds the whole individual, may acquire a prismatic structure, it is secreted by the protoplasmic threads which project through certain pores definitely situated in the walls (Fig. 35 A, B).

VEGETATIVE MULTIPLICATION takes places by division. A good example of this is found in Cosmarium botrytis (Fig. 36 A-D). The nucleus and chromatophores divide, and simultaneously the central indentation becomes deeper, the outer wall is then ruptured making a circular aperture through which the inner wall protrudes forming a short, cylindrical canal between the two halves to which it is attached (Fig. 36 C). After elongation the canal is divided by a central transverse wall, which commences as a ring round its inner surface and gradually forms a complete septum. The dividing wall gradually splits, and the two individuals separate from each other, each one having an old and a new half. The two daughter-cells bulge out, receive a supply of contents from the parent-cells, and gradually attain their mature size and development (Fig. 36 B-D). Exceptions to this occur in some forms.

CONJUGATION takes place in the simplest way in Mesotænium, where the two conjugating cells unite by a short tube (conjugation-canal), which is not developed at any particular point. The aplanogametes merge together after the dissolution of the dividing wall, like two drops of water, almost without any trace of preceding contraction, so that the cell-wall of the zygote generally lies in close contact with the conjugating cells. The conjugating cells in the others lie either transversely (e.g. Cosmarium, Fig. 37 d; Staurastrum, etc.), or parallel to one another (e.g. Penium, Closterium, etc.), and emit a short conjugation-canal (Fig. 37 d) from the centre of that side of each cell which is turned towards the other one. These canals touch, become spherical, and on the absorption of the dividing wall the aplanogametes coalesce in the swollen conjugation-canal (Fig. 37 e), which is often surrounded by a mucilaginous envelope. The zygote, which is often spherical, is surrounded by a thick cell-wall, consisting of three layers; the outermost of these sometimes bears thorn-like projections, which in some species are simple (Fig. 37 f), in others branched or variously marked; in some, however, it remains always smooth (e.g. Tetmemorus, Desmidium). Deviation from this mode of conjugation may occur within certain genera (e.g. Closterium, Penium). Upon germination the contents of the zygote emerge, surrounded by the innermost layers of the wall (Fig. 37 g, h) and generally divide into two parts which develop into two new individuals, placed transversely to each other (Fig. 37 i); these may have a somewhat more simple marking than is generally possessed by the species.

The most frequent genera are:--

A. Solitary cells: MESOTÆNIUM, PENIUM (Fig. 38 B), CYLINDROCYSTIS, EUASTRUM (Fig. 38 D), MICRASTERIAS (Fig. 38 C), COSMARIUM (Fig. 36, 37), XANTHIDIUM, STAURASTRUM (Fig. 38 E), PLEUROTÆNIUM, DOCIDIUM, TETMEMORUS, CLOSTERIUM (Fig. 38 A), SPIROTÆNIA.

B. Cells united into filaments: SPHÆROZOSMA, DESMIDIUM, HYALOTHECA, GYMNOZYGA, ANCYLONEMA, GONATOZYGON.

Order 2. =Zygnemaceæ.= Cell-wall without markings. The cells are cylindrical, not constricted in the centre, and (generally) united into simple, unbranched filaments. The whole contents of the conjugating cells take part in the formation of the zygote, which on germination grows out directly into a new filament.

Spirogyra is easily recognised by its spiral chlorophyll band; Zygnema has two star-like chromatophores in each cell (Fig. 40); both these genera are very common Algæ in ponds and ditches.

The conjugation among the Zygnemaceæ takes place in the following manner: the cells of two filaments, lying side by side, or two cells, the one being situated above the other in the same filament (Fig. 41), push out small protuberances opposite each other (Fig. 39 A, a, b); these finally meet, and the dividing wall is absorbed so that a tube is formed connecting one cell with the other; the protoplasmic contents round off, and the whole of these contents of one of the cells glides through the conjugation-tube and coalesces with that of the other (Fig. 39 B), the aggregate mass then rounds off, surrounds itself with a cell-wall, and becomes a zygote. A distinct difference may be found between the cells in the two filaments, those in the one whose protoplasmic contents pass over being cylindrical, while those of the recipient one are more barrel-shaped, and of a larger diameter. The former may be regarded as a male, the latter as a female plant. The zygote germinates after a period of rest, and grows out into a new filament (Fig. 42).

Order 3. =Mesocarpaceæ.= The cell-walls are glabrous, unconstricted in the centre, and united into simple unbranched filaments. The chromatophore consists of an axial chlorophyll-plate, with several pyrenoids. The zygote is formed by the coalescence of two cells (Fig. 43) (sometimes three or four), but the whole protoplasmic contents of the cells do not take part in this process, a portion always remaining behind; the aplanogametes coalesce in the conjugation-canal. The zygote thus formed appears incapable of germination until after 3–5 divisions. Of the cells so formed, only one is fertile, the sterile cells, according to Pringsheim, constituting a rudimentary sporocarp. The germinating cells grow out into a new filament. In this order, conjugation has been observed between two cells of the same filament. The Mesocarpaceæ thrive best in water which contains lime.

Class 6. =Chlorophyceæ (Green Algæ).=

These Algæ are coloured green by chlorophyll, seldom in combination with other colouring matter, and then especially with red. The product of assimilation is frequently starch, which generally accumulates round certain specially formed portions of protoplasm termed pyrenoids. The thallus is uni- or multicellular; in the higher forms (certain Siphoneæ) the organs of vegetation attain differentiation into stem and leaf. The asexual reproduction takes place in various ways; the sexual reproduction is effected by conjugation of motile gametes, or by oogamous fertilisation. The swarm-cells (zoospores, gametes, and spermatozoids) are constructed symetrically, and have true protoplasmic cilia, these generally being attached to the front end of the swarm-cells. Most of these Algæ live in water (fresh or salt); some are found upon damp soil, stones, or tree-stems, and some live enclosed in other plants.

The Class is divided into three families:--

1. PROTOCOCCOIDEÆ: Volvocaceæ, Tetrasporaceæ, Chlorosphæraceæ, Pleurococcaceæ, Protococcaceæ, Hydrodictyaceæ.

2. CONFERVOIDEÆ: Ulvaceæ, Ulothricaceæ, Chætophoraceæ, Mycoideaceæ, Cylindrocapsaceæ, Œdogoniaceæ, Coleochætaceæ, Cladophoraceæ, Gomontiaceæ, Sphæropleaceæ.

3. SIPHONEÆ: Botrydiaceæ, Bryopsidaceæ, Derbesiaceæ, Vaucheriaceæ, Phyllosiphonaceæ, Caulerpaceæ, Codiaceæ, Valoniaceæ, Dasycladaceæ.

Family 1. =Protococcoideæ.=

The Algæ which belong to this group are uni- or multicellular with the cells more or less firmly connected, sometimes in a definite, sometimes in an indefinite form (Fig. 47). Colonies are formed either by division or by small unicellular individuals becoming united in a definite manner; the colonies formed in this latter way are termed Cœnobia. Apical cells and branching are absent. Multiplication by division; asexual reproduction by zoospores, rarely by akinetes. Sexual reproduction may be wanting, or it takes place by isogamous, rarely by oogamous fertilisation.

Some are attached by means of a stalk to other objects (Characium, Fig. 49), others occur as “Endophytes” in the tissues of certain Mosses or Phanerogams, e.g. Chlorochytrium lemnæ, in Lemna trisulca; Endosphæra, in the leaves of Potamogeton, Mentha aquatica, and Peplis portula; Phyllobium, in the leaves of Lysimachia nummularia, Ajuga, Chlora, and species of Grasses; Scotinosphæra in the leaves of Hypnum and Lemna trisulca; the majority, however, live free in water and in damp places. Many species which were formerly considered to belong to this family have been proved to be higher Algæ in stages of development.

Order 1. =Volvocaceæ.= The individuals in this order are either uni- or multicellular, and during the essential part of their life are free-swimming organisms. They are generally encased in a mucilaginous envelope, through which 2–6 cilia project from every cell. The vegetative reproduction takes place by the division of all, or a few, of the cells of the individual; in some a palmella-stage is found in addition. The sexual reproduction takes place by isogamous or oogamous fertilisation.

The Volvocaceæ may be considered to include the original forms of the Chlorophyceæ, because, among other reasons, the motile stage is here the most prominent; they also form the connecting link between the animal Flagellata, and forms intermediate to the Syngeneticæ may perhaps be found amongst them. Three series of green Algæ may be supposed to have taken their origin from the Volvocaceæ: CONJUGATEÆ (Desmidiaceæ) which have lost the swarming stage, but whose conjugation is the nearest to the fertilisation in Chlamydomonas pulvisculus: the PROTOCOCCACEÆ in which the vegetative divisions have disappeared, while the swarming stage continues to be present, though of shorter duration; and TETRASPORACEÆ, in which the vegetative divisions are more prominent, whilst the swarming stage is less so.

A. UNICELLULAR INDIVIDUALS. The principle genera are: Chlamydomonas, Sphærella, Phacotus.--Sphærella nivalis is the Alga which produces the phenomenon of “Red Snow,” well known on high mountains and on ice and snow fields in the polar regions. The red colouring matter which appears in this and other green Algæ, especially in the resting cells, is produced by the alteration of the chlorophyll.

Phacotus lenticularis has an outer covering incrusted with lime, which, at death, or after division, opens out into two halves. Species may be found among Chlamydomonas, in which conjugation takes place between gametes of similar size without cell-wall, but in C. pulvisculus conjugation takes place between male and female aplanogametes which are surrounded by a mucilaginous envelope.

B. MULTICELLULAR INDIVIDUALS. The most important genera are Gonium, Stephanosphæra, Pandorina, Eudorina, Volvox.--Gonium has 4 or 16 cells arranged in a definite pattern in a flat plate (Fig. 44). Pandorina (Fig. 45), has 16 cells arranged in a sphere (Fig. 45 A). The vegetative reproduction takes place in this way: each cell, after having rounded off, and after the withdrawal of the cilia, divides itself into 16 new ones (Fig. 45 B), each forming a new individual, which soon grows to the size of the mother-individual. It was in this Alga that the conjugation of self-motile gametes was first discovered by Pringsheim, 1869. When conjugation is about to take place, each cell divides into sixteen, as in vegetative reproduction, but the 16 × 16 cells all separate from one another (Fig. 45 C, female gametes, and D, male gametes), and swarm solitarily in the water. The male are, most frequently, smaller than the female, but otherwise they are exactly alike; they are more or less pear-shaped, with a colourless anterior end, 2 cilia, a red “eye-spot,” etc. After swarming for some time they approach each other, two and two, generally a large and a smaller one, and come into contact at their colourless end; in a few moments they coalesce and become one cell (Fig. 45 E, F), this has at first a large colourless anterior end, 4 cilia, and 2 “eye-spots” (Fig. 45 G), but these soon disappear and the cell becomes uniformly dark-green and spherical, and surrounds itself with a thick cell-wall, losing at the same time its power of motion: the zygote (Fig. 45 H) is formed, and becomes later on a deep red colour. On the germination of the zygote, the protoplasmic cell-contents burst open the wall (Fig. 45 J), and emerge as a large swarmspore (Fig. 45 K) which divides into 16 cells, and the first small individual is formed (Fig. 45 L, M).

Eudorina is like Pandorina in structure, but stands somewhat higher, since the contrast between the conjugating sexual cells is greater, the female one being a motionless oosphere.

The highest stage of development is found in Volvox (Fig. 46). The cells are here arranged on the circumference of a sphere, and enclose a cavity filled with mucilage. The number of these cells may vary from 200–22,000, of which the majority are vegetative and not reproductive, but some become large, motionless oospheres (Fig. 46 b); others, which may appear as solitary individuals, divide and form disc-shaped masses of from 8–256 small spermatozoids (Fig. 46 a). After the oosphere has been fertilised by these, the oospore surrounds itself by a thick, sometimes thorny cell-wall, and on germination becomes a new individual of few cells. A few cells conspicuous by their larger size may be found (1–9, but generally 8) in certain individuals, and these provide the vegetative reproduction, each forming by division a new individual.

Order 2. =Tetrasporaceæ= reproduce both by vegetative divisions and swarmspores, some have also gamete-conjugation. The principal genera are: Tetraspora, Apiocystis, Dactylococcus, Dictyosphærium, Chlorangium.

Order 3. =Chlorosphæraceæ.= Chlorosphæra.

Order 4. =Pleurococcaceæ.= In this order the swarm-stages and sexual reproduction are entirely absent. Vegetative reproduction by division. The principal genera are: Pleurococcus (Fig. 47), Scenedesmus (Fig. 48), Raphidium, Oocystis, Schizochlamys, Crucigenia, Selenastrum.--Pleurococcus vulgaris (Fig. 47) is one of the most common Algæ throughout the world, occurring as green coverings on tree-stems, and damp walls, and it is one of the most common lichen-gonidia.

Order 5. =Protococcaceæ.= The cells are motionless, free or affixed on a stalk (e.g. Characium, Fig. 49), either separate or loosely bound to one another; they never form multicellular individuals. Multiplication by division is nearly always wanting. Reproduction takes place by swarmspores, which have 1 or 2 cilia, and sexual reproduction in some by gamete-conjugation. The principal genera are: Chlorococcum, Chlorochytrium, Chlorocystis, Scotinosphæra, Endosphæra, Phyllobium, Characium, Ophiocytium, Sciadium.

Order 6. =Hydrodictyaceæ.= The individuals are unicellular but several unite after the zoospore-stage into definitely formed families (cœnobia). Ordinary vegetative division is wanting, but asexual reproduction takes place by zoospores (or by motionless cells without cilia), which unite and form a family similar to the mother-family, inside the mother-cell, or in a mucilaginous envelope. Where sexual reproduction is found it takes place by gamete-conjugation. The principal genera are: Pediastrum (Fig. 50), Cœlastrum, Hydrodictyon (Fig. 51).

The cœnobium of Hydrodictyon reticulatum (Water-net) is formed of a large number of cells which are cylindrical, and attached to one another by the ends (Fig. 51). The asexual reproduction takes place by zoospores, which are formed in large numbers (7,000–20,000) in each mother-cell, within which they move about for a time, and then come to rest and arrange themselves into a new net (Fig. 51 A) which is set free by the dissolution of the wall of the mother-cell, grows, and becomes a new cœnobium. The sexual reproduction takes place by gamete-conjugation. The gametes are formed in the same manner as the zoospores, but in larger numbers (30,000–100,000), and swarm out of the mother-cell (Fig. 51 B). The zygote forms, on germination, 2–5 large zoospores, each with one or two cilia, these generally swarm about for a time, and after a period of rest become irregular thorny bodies (polyhedra); their contents again divide into zoospores, the thorny external coating of the polyhedra is cast off, and the zoospores, surrounded by the dilated internal coating, unite to form a small family, which produces several others in the manner described.

Family 2. =Confervoideæ.=

The individuals are always multicellular, the cells firmly bound together and united into unbranched or branched filaments, expansions, or masses of cells which grow by intercallary divisions or have apical growth. In the first seven orders the cells are uninuclear, but the cells of the remaining three orders contain several nuclei. Asexual reproduction by zoospores, akinetes or aplanospores. Sexual reproduction by isogamous or oogamous fertilisation.

The Confervoideæ, through the Ulvaceæ, are connected with the Tetrasporaceæ, and from the Coleochætaceæ, which is the most highly developed order, there are the best reasons for supposing that the Mosses have taken their origin. The Cladophoraceæ show the nearest approach to the Siphoneæ.

Order 1. =Ulvaceæ.= The thallus consists of one or two layers of parenchymatous cells, connected together to form either a flat membrane (Monostroma, Ulva) or a hollow tube (Enteromorpha), and may be either simple, lobed, or branched. Reproduction takes place by detached portions of the thallus; or asexually by zoospores or akinetes. Gamete-conjugation is known to take place in some members of this order, the zygote germinating without any resting-stage. The majority are found in salt or brackish water.

Order 2. =Ulothricaceæ.= The thallus consists normally of a simple unbranched filament (sometimes a small expansion consisting of one layer of cells is formed, as in Schizomeris and Prasiola which were formerly described as separate genera). Asexual reproduction takes place by means of zoospores (with 1, 2, or 4 cilia), akinetes or aplanospores; the last named may germinate immediately, or only after a period of rest. Sexual reproduction takes place by the conjugation of gametes of about the same size, each having two cilia (Fig. 52 d). The zygote of Ulothrix, on germination, produces a brood of zoospores which swarm for a time and then elongate to become Ulothrix-filaments (alternation of generations). The gametes may also germinate without conjugation in the same manner as the zoospores. The principal genera are: Ulothrix, Hormidium, Conferva, Microspora.--Ulothrix zonata is very common in running fresh water. Nearly all the species of Hormidium occur on damp soil, tree-stems and stones.

Order 3. =Chætophoraceæ.= The thallus consists of a single, branched, erect or creeping filament of cells, often surrounded by mucilage. The cells have only one nucleus. Asexual reproduction by zoospores with 2 or 4 cilia, by akinetes, or aplanospores. In many, conjugation between gametes with 2 cilia may be found. They approach on one side, Ulothricaceæ, and on the other, Mycoideaceæ. The principal genera are: Stigeoclonium, Draparnaldia, Chætophora, Entoderma, Aphanochæte, Herposteiron, Phæothamnion, Chlorotylium, Trichophilus, Gongrosira, Trentepohlia. Most of the species of Trentepohlia are coloured red by the presence of a red colouring material, which occurs in addition to the chlorophyll. They are aerial Algæ which live on stones (T. jolithus, “violet stone,” so named on account of its violet-like odour in rainy weather), on bark and old wood (T. umbrina), or on damp rocks (T. aurea). Trichophilus welckeri lives in the hair of Bradypus.

Order 4. =Mycoideaceæ.= The thallus is discoid, consisting of one or more cell-layers, and is always attached. Asexual reproduction by zoospores with 2 or 4 cilia. Sexual reproduction in some species by the conjugation of gametes with 2 cilia. This order forms the connecting link between Chætophoraceæ and Coleochætaceæ. The species occur in fresh water (Chætopeltis) as well as in salt (Pringsheimia), on the carapace of tortoises (Dermatophyton = Epiclemmydia), or endophytic between the cuticle and the epidermal cells of the leaves of tropical plants, destroying the leaf-tissue (Mycoidea).

Order 5. =Cylindrocapsaceæ.= The thallus consists of a simple (rarely, in parts, formed of many rows) unbranched filament, attached in the young condition, which has short cells with a single nucleus, and is enveloped in a thick envelope with a laminated structure. Asexual reproduction by zoospores with 2 cilia, which are formed 1, 2, or 4 in each vegetative cell. The antheridia are produced by a single cell, or a group of cells, in a filament, dividing several times without increasing in size. Two egg-shaped spermatozoids, each with 2 cilia (Fig. 53 D), are formed in each antheridium, and escape through an aperture in the side; in the first stages they are enclosed in a bladder-like membrane (Fig. 53 B, C). Other cells of the filament swell out and form oogonia (Fig. 53 A), which resemble those of Œdogonium. After fertilisation, the oospore surrounds itself with a thick wall, and assumes a reddish colour. The germination is unknown. The unfertilised oospheres remain green, divide often into 2–4 daughter-cells, and grow into new filaments.

This order, which only includes one genus, Cylindrocapsa, forms the connecting link between Ulothricaceæ and Œdogoniaceæ. The few species (4) occur only in fresh water.

Order 6. =Œdogoniaceæ.= The thallus consists of branched (Bulbochæte) or unbranched (Œdogonium) filaments, attached in the early stages. The cells may be longer or shorter, and have one nucleus. Asexual reproduction by zoospores, which have a chaplet of cilia round the base of the colourless end (Fig. 6 a). Sexual reproduction takes place by oogamous fertilisation. On the germination of the oospore, 4 zoospores are formed (Fig. 54 F). They occur only in fresh or slightly brackish water. The division of the cells takes place in quite a peculiar and unusual manner. At the upper end of the cell which is about to divide, a ring-shaped thickening of soft cellulose is formed transversely round the wall; the cell-nucleus of the mother-cell and the protoplasm then divide by a transverse wall into two portions of similar size, and the cell-wall bursts transversely along the central line of the thickened ring. The cell-wall thus divides into two parts--the upper one short, the “cap,” and the lower one much longer, the “sheath.” The portions of the original cell-wall now separate from each other, the cellulose ring extending, and supplying an additional length of cell-wall between them. The cap and sheath will project a little in front of the piece thus inserted. The dividing wall between the two new cells is formed near to the uppermost edge of the sheath, and gradually becomes thicker and firmer. The inserted piece of wall forms the larger part of the wall of the upper cell: the remainder is formed by the cap. This mode of division is repeated exactly in the same way, and new caps are formed close below the first one, one for every division.

Fertilisation takes place in the following way. The oogonium is a large ellipsoidal, swollen cell (og, in Fig. 54 A), whose contents are rounded off into an oosphere with a colourless receptive-spot (see B); an aperture is formed in the wall of the oogonium, through which the spermatozoids are enabled to enter (B). The spermatozoids are produced either directly, as in D (in pairs), in basal cells of the filament, or indirectly. In the latter case a swarmspore (androspore) is formed which comes to rest, attaches itself to an oogonium, germinates, and gives rise to a filament of a very few cells--dwarf-male (A, B, m). The spermatozoids are formed in the upper cell of the dwarf-male (m), and are set free by the summit of the antheridium lifting off like a lid. On the germination of the oospore (C), which takes place in the following spring, 4 zoospores are produced (F) (i.e. the sexual generation); these swarm about for a time, and ultimately grow into new filaments.

Order 7. =Coleochætaceæ.= The thallus is always attached, and of a disc- or cushion-shape, formed by the dichotomous branching of filaments of cells united in a pseudo-parenchymatous manner. Each cell has only one nucleus. Asexual reproduction by zoospores with 2 cilia (Fig. 55 D), which may arise in all the cells. Sexual reproduction by oogamous fertilisation. The spermatozoids resemble the swarmspores, but are smaller (E), and originate singly (in the species figured) in small conical cells (c, d in A). The oogonia are developed at the extremities of certain branches: they are bottle-shaped cells with very long and thin necks (trichogyne), open at the end (a in A); at the base of each oogonium is a spherical oosphere. The spermatozoids reach the oosphere through the trichogyne, or through an aperture in the wall when the trichogyne is absent, and fertilisation having taken place, the oogonium becomes surrounded by a cell-layer (envelope), which grows out from the cells near its base (b in A), and in this way a kind of fruit is formed (B) (spermocarp, cystocarp).

The oospore, next spring, divides and forms a parenchymatous tissue (homologous with the Moss-sporophyte); this bursts open the envelope (C), and a zoospore (homologous with the spores of the Moss-capsule) arises in each of the cells, and produces a new Coleochæte. We have then, in this case, a still more distinct alternation of generations than in Œdogonium. Only one genus, Coleochæte, is known, but it contains several species, all living in fresh water.

Order 8. =Cladophoraceæ.= This order is probably derived from the Ulothricaceæ. The thallus consists of a single, unbranched or branched filament, generally with an apical cell. The cells have each 2 or more nuclei. Asexual reproduction by zoospores with 2 or 4 cilia, and by akinetes. Conjugation of gametes with 2 cilia is found in some genera. They occur in salt as well as in fresh water. The principal genera are: Urospora, Chætomorpha, Rhizoclonium, Cladophora; of the last named genus the species C. lanosa and C. rupestris are common in salt water; C. fracta and C. glomerata in fresh water.

Order 9. =Gomontiaceæ.= Gomontia polyrrhiza, the only species hitherto known, is found on old calcareous shells of certain salt water Molluscs.

Order 10. =Sphæropleaceæ.= The thallus consists of free, unbranched filaments, with very elongated multinuclear cells. The vegetative cells form no zoospores. Sexual reproduction by oogamous fertilisation (see page 13, Fig. 10 B). The oospore has a thick wall (Fig. 10 D) studded with warts, and assumes a colour resembling red lead. It germinates only in the following spring, and produces 1–8 zoospores, each with 2 cilia (Fig. 10 E), which grow into new filaments. Only one species, Sphæroplea annulina, is known.

Family 3. Siphoneæ.

The thallus has apical growth, and in the vegetative condition consists generally of one single (in the Valoniaceæ most frequently of more) multinuclear cell, which may be much branched, and whose separate parts in the higher forms (e.g. Bryopsis, Fig. 57; Caulerpa, Fig. 59, etc.) may be differentiated to perform the various physiological functions (as root, stem and leaf). Vegetative multiplication by detached portions of the thallus (gemmæ); asexual reproduction by zoospores, akinetes, or aplanospores. Sexual reproduction by gamete-conjugation, rarely by oogamous fertilisation. The zygote or oospore germinates as a rule without any resting-stage.

Most of the Siphoneæ occur in salt water or on damp soil. Many (e.g. Dasycladaceæ) are very much incrusted with lime, and occur, in the fossilized condition, in the deposits from the Cretaceous period to the present time. The Siphoneæ are connected by their lowest forms (Botrydiaceæ or Valonia) with the Protococcaceæ, but show also, through the Valoniaceæ, points of relationship to the Cladophoraceæ.

Order 1. =Botrydiaceæ.= The thallus in the vegetative condition is unicellular, club-shaped, with a small single (Codiolum) or repeatedly dichotomously branched system of colourless rhizoids (Botrydium, Fig. 56 a), by which it is attached to objects immersed in salt water (Codiolum) or to damp clay soil (Botrydium). Asexual reproduction by zoospores with one (Botrydium) or two cilia, and by aplanospores. The sexual reproduction is only known in Botrydium, and takes place in the following manner: in the part of the thallus which is above ground and in an active vegetative condition, several round cells (Fig. 56 c) are formed, which may be green or red according as they grow under water, or exposed to the strong light of the sun. These cells must be considered as “gametangia” as they produce many gametes (d) provided with two cilia. The zygote (h, i) formed by the conjugation (e, f, g) may either germinate immediately, or become a thick-walled resting-cell of an irregular, angular form.

Order 2. =Bryopsidaceæ.= The thallus in the vegetative condition is unicellular, and consists at the lower extremity of branched rhizoids, while the upper portion is prolonged into a stem-like structure of unlimited growth, producing, acropetally, branches and leaf-like structures. The latter have limited growth, and are separated by a cross wall from the stem, and become gametangia, or drop off. The gametes have two cilia, and are of two kinds: the female, which are green and large and the male, which are of brownish colour and smaller. Zoospores or any other method of asexual reproduction are unknown. Only one genus, Bryopsis, living in salt water.

Order 3. =Derbesiaceæ.= Only one genus, Derbesia, living in saltwater. The zoospores, which are formed in a few lateral, swollen zoosporangia, possess one nucleus which has arisen through the coalescence of several, and they resemble the zoospores of Œdogonium by having a circle of cilia attached at the base of the colourless spot.

Order 4. =Vaucheriaceæ.= The thallus consists, in the vegetative condition, of a single irregularly or dichotomously branched cell, without differentiation into stem or leaf; root-like organs of attachment may however occur. Asexual reproduction by zoospores, which are formed singly in the extremity of a branch cut off by a transverse wall. They contain many nuclei, and bear small cilia situated in pairs, which give the appearance of a fine “pile” covering the whole or a great part of the surface. Akinetes, aplanospores, and phytoamœbæ (naked masses of protoplasm, without cilia, which creep like an amœba on a substratum) may occur under certain conditions.

The sexual reproductive organs are formed on short lateral branches, and are separated from the vegetative cell (Fig. 58 A) by cell-walls. Numerous spermatozoids, each with two cilia, are developed in the coiled antheridium (A, b). The oogonium is a thick, egg-shaped, often oblique cell, with its protoplasm rounded into an oosphere, which has a hyaline “receptive-spot” (A, a) immediately beneath the aperture formed in the wall of the oogonium. A slimy mass, which serves to receive the spermatozoids, is formed in some species in this aperture. The spermatozoids when liberated swim towards and enter the oosphere, which then immediately surrounds itself with a thick cell-wall. The mature oospore (B) contains a large quantity of oil. At germination the outer cell-wall bursts and a new plant is formed. There is only one genus, Vaucheria, with species living in salt as well as in fresh water and on damp soil.

Order 5. =Phyllosiphonaceæ= are parasites in the leaves and stalks of Flowering-plants.

Order 6. =Caulerpaceæ.= The thallus has distinct differentiation into root, stem and leaf-like members (Fig. 59); it is unicellular. Within the cell, strong, branched threads of cellulose extend from one side to the other serving as stays to support the thallus. Reproduction takes place by detached portions of the thallus; no other modes of reproduction are known. This order may most approximately be classed with the Bryopsidaceæ. The genus Caulerpa consists of more than seventy species which inhabit the tropical seas.

Order 7. =Codiaceæ.= The thallus has various forms, but without distinct differentiation in stem- or leaf-structures, sometimes (e.g. Halimeda) it is very much incrusted with lime. In the early stages it is unicellular (later, often multicellular), very much branched, with the branches, at any rate partly, so united or grown in amongst one another (Fig. 60) that an apparently parenchymatous cellular body is formed. Akinetes or aplanospores are wanting; zoospores (or gametes?) may be developed in some species, however, in special swollen sporangia. Fertilisation similar to that in Bryopsis occurs perhaps in Codium. They are all salt water forms.

Order 8. =Valoniaceæ.= The thallus is generally multicellular, without differentation into stem- or leaf-structures, but the cells are sometimes united together and form a leaf-like reticulate expansion (e.g. Anadyomene). Zoospores are known in some, and they are then formed directly in the vegetative cells. In others (e.g. Valonia), a mass of protoplasm, which maybe separated through the damaging of a cell, can surround itself with a cell-wall, and grow into a new plant. No other modes of reproduction are known. The most important genera are: Valonia, Siphonocladus, Chamædoris, Struvea, Microdictyon, Anadyomene. They are all salt water forms.

As already pointed out, the Valoniaceæ occupy a somewhat central position among the Siphoneæ, and present points of similarity and contrast with the Botrydiaceæ and the Bryopsidaceæ through Valonia, with the Dasycladaceæ through Chamædoris, and also with the Cladophoraceæ through Siphonocladus, and Struvea.

Order 9. =Dasycladaceæ.= The thallus consists of an axile longitudinal cell, destitute of transverse walls, attached at the base by root-like organs of attachment, and producing acropetally whorls of united, single or branched, leaf-like structures with limited growth. Asexual reproduction is wanting. Sexual reproduction by conjugation of gametes which arise in separate, fertile leaves, either directly or from aplanospores, which develope into gametangia. The principal genera are: Acetabularia, Dasycladus, Neomeris, Cymopolia. All marine.

The curiously shaped Acetabularia mediterranea grows gregariously on limestone rocks, and shells of mussels in the Mediterranean; it resembles a minute umbrella with a small stem, sometimes as much as nine centimetres in height, and a shade which may be more than one centimetre in diameter. The cell-membrane is thick, and incrusted with carbonate and oxalate of lime. Only the lower, root-like part of the thallus, which penetrates the calcareous substratum survives the winter, and may grow up into a new plant. The sterile leaves, which drop off early, are dichotomously branched and formed of cylindrical cells separated from each other by cross-walls, but they are not grown together. The shade is formed by a circle of 70–100 club-shaped rays (fertile leaves) grown together, in each ray 40–80 aplanospores are formed, which become liberated at the breaking of the shade, and later on are changed to gametangia (compare Botrydium) which open by a lid and allow a large number of egg-shaped gametes with two cilia to escape. Gametes from various gametangia conjugate with one another; the product of the conjugation swarms about for some time, rounds off, and then surrounds itself with a cell-wall. The zygote germinates after a period of rest and then produces a sexual plant. The aplanospores (gametangia) thus represent the sexual generation.

Class 7. =Characeæ.=

The thallus has a stem with nodes and internodes; and whorls of leaves, on which may be developed the antheridia and oogonia, are borne at the nodes. Vegetative reproduction by bulbils and accessory shoots. Zoospores are wanting. The antheridia are spherical, and contain a number of filaments in which the spirally coiled spermatozoids, each with two cilia, are formed. The oogonium is situated terminally, and is at first naked, but becomes later on surrounded by an investment, and forms after fertilisation the so-called “fruit.” The oospore, after a period of rest, germinates by producing a “proembryo,” from which the young sexual plant arises as a lateral branch. The Characeæ are distinguished by the structure of their vegetative system as well as by the spirally-coiled spermatozoids, and stand as an isolated group among the Thallophytes, of which, however, the Siphoneæ appear to be their nearest relations. They were formerly, but wrongly, placed near the Mosses. The class contains only one order, the Characeæ.

Order 1. =Characeæ.= Algæ with a peculiar odour, often incrusted with lime, and of a brittle nature. They generally grow gregariously in large masses at the bottom of fresh and brackish water, and are from a few inches to more than a foot in height. The stem has long internodes which in Nitella are formed of one cylindrical cell; in Chara of a similar cell, but closely surrounded by a cortical layer of smaller ones. The protoplasm in contact with the cell-wall exhibits in a well-marked degree the movement of rotation (cyclosis), carrying the chlorophyll corpuscles along with it. The internodes are separated from each other by a layer of small cells (nodal cells) from which the leaves are produced. The leaves are borne in whorls of from 5–12 which regularly alternate with one another as in the higher verticillate plants; a branch is borne in the axil of the first formed leaf of each whorl (Fig. 61 A, n).

The leaves are constructed in the same manner as the stem; they are divided into a series of joints, but have only a limited power of growth; their terminal cell, too, is not enclosed by a cortex. Leaflets are borne at their nodes. The growth of the stem is unlimited, and proceeds by means of an apical cell (Fig. 62 s). The apical cell divides into a segment-cell and a new apical cell. The segment-cell then divides by a transverse wall into two cells, one lying above the other; the lower one, without any further division, becomes one of the long, cylindrical, internodal cells (Fig. 62 in), and the upper one (Fig. 62 n) divides by vertical walls to form the nodal cells. The cortical cells (Fig. 62 r) which surround the long internodal cells of Chara, are derived from the divisions of the nodal cells; the cells covering the upper portion of an internodal cell being derived from the node immediately above it, and those in the lower part of the internode from the node below it.

The organs of reproduction are very conspicuous by their colour and form. They are always situated on the leaves, the plants being very frequently monœcious. The antheridia (Fig. 61 B, a) are modified leaflets or the terminal cell of a leaf; they are spherical and become red when mature. Their wall consists of 8 “shields,” i.e. of plate-like cells, 4 of which cover the upper half, and are triangular; the 4 round the lower half, to which the stalk of the antheridia is attached, being quadrilateral, with sides of unequal length. The shields (Fig. 61 C) have dentated edges, with the teeth fitting into one another, and their faces ornamented with ridges. From the centre of the internal face of each shield (C) a cylindrical cell, the manubrium, projects nearly as far as the centre of the antheridium; at the inner end of each of the manubria a spherical cell, the capitulum, is situated. Each capitulum bears six secondary capitula, from each of which four long coiled filaments (C, D) project into the cavity of the antheridium. These filaments are divided by transverse walls into from 100–200 discoid cells, in each of which a biciliated, coiled spermatozoid is developed (D, E) from the nucleus. The spermatozoids escape from their mother-cell and are set free by the shields separating from one other.

The female organ of reproduction (Fig. 61 B, 63) is a small modified shoot, whose apical cell functions as an oogonium, its protoplasm forming the oosphere, which has a colourless receptive-spot at the summit (Fig. 63 u). The oogonium is situated on a nodal cell, from which 5 cells grow out in a circle and coil round the oogonium, covering it with a close investment. These cells divide once or twice at the top, so that 5 or 10 small cells are cut off, which project above the oogonium and form the so-called “crown” (Fig. 63 k). The crown either drops off at fertilisation, or its cells separate to form a central canal for the passage of the spermatozoids. The wall of the oosphere[9] above the receptive spot becomes mucilaginous, and allows the spermatozoid to fuse with the oosphere. The oospore, on germination (Fig. 64 sp), becomes a small filamentous plant of limited growth (Fig. 64 i, d, q, pl)--the proembryo--and from this, as a lateral outgrowth, the sexual generation is produced.

The order is divided into two sub-orders:--

A. NITELLEÆ. The crown consists of 10 cells; cortex absent: Nitella, Tolypella.

B. CHAREÆ. The crown consists of 5 cells; cortex present: Tolypellopsis, Lamprothamnus, Lychnothamnus, Chara.

Chara crinita is parthenogenetic; in large districts of Europe only female plants are found, yet oospheres are formed capable of germination.

About 40 species of fossilized Chara, determined by their carpogonia, are known in the geological formations from the Trias up to the present day.

Class 8. =Phæophyceæ (Olive-Brown Seaweeds).=

The Phæophyceæ are Algæ, with chromatophores in which the chlorophyll is masked by a brown colour (phycophæin). The product of assimilation is a carbohydrate (fucosan), never true starch. In the highest forms (Fucaceæ), the thallus presents differentiation into stem, leaf, and root-like structures. The asexual reproduction takes place by means of zoospores. The sexual reproduction is effected by the coalescence of motile gametes, or by oogamous fertilisation. The swarm-cells are monosymmetric, each moved by two cilia which are true protoplasmic structures, and generally attached laterally (Fig. 65). The Phæophyceæ are almost entirely saltwater forms; a few species of Lithoderma live in fresh water.

The class is divided into two families:--

1. PHÆOSPOREÆ: 1 Sub-Family, Zoogonicæ; 2 Sub-Family, Acinetæ.

2. CYCLOSPOREÆ: Fucaceæ.

Family 1. =Phæosporeæ.=

The family consists of multicellular plants, whose cells are firmly united together to form a thallus; this, in the simplest cases, may be a branched filament of cells (Ectocarpus), or, in the highest, may resemble a stem with leaves (Laminariaceæ), while all transitional forms may be found between these two. The thallus grows by intercalary divisions (e.g. Ectocarpus), or by an apical cell (e.g. Sphacelaria); pseudo-parenchymatous tissue may sometimes be formed by cells, which were originally distinct, becoming united together. The size of the thallus varies; in some species it is quite small--almost microscopical,--while in the largest it is many metres in length.

The vegetative cells in the lower forms are nearly uniform, but in those which are more highly developed (Laminariaceæ and Fucaceæ), they are sometimes so highly differentiated that mechanical, assimilating, storing and conducting systems may be found; the last named systems are formed of long cells with perforated, transverse walls, which bear a strong resemblance to the sieve-tubes in the higher plants.

The colouring matter in the living cells (“phæophyl”) contains chlorophyll; but this is concealed by a brown (“phycophæin”), and a yellow (“phycoxanthin”) colouring material, and hence all these Algæ are a lighter or darker yellow-brown. Starch is not formed. Asexual reproduction takes place, (1) by zoospores which arise in unilocular zoosporangia, and are monosymmetric, with two cilia attached laterally at the base of the colourless anterior end (Fig. 65), the longer one being directed forwards and the shorter backwards; or (2) by aplanospores (?).

Sexual reproduction has only been discovered in a few cases, and takes place by means of gametes (oogamous fertilisation perhaps occurs in the Tilopteridæ). The gametes have the same structure as the zoospores, and arise in multilocular gametangia; these, like the zoosporangia, are outgrowths from the external surface, or arise as modifications from it. The conjugating gametes may be similar (e.g. Ectocarpus pusillus), or there may be a more or less pronounced difference of sex, an indication of which is found in Ectocarpus siliculosus (Fig. 66). When the gametes in this species have swarmed for a time, some, which are generally larger, are seen to attach themselves by one of the cilia, which by degrees is shortened to form a kind of stalk (compare the upper gamete in Fig. 66 II); these are the female gametes, which now become surrounded by a number of males endeavouring to conjugate with them, but only one succeeds in effecting fertilisation. The protoplasm of the two gametes coalesces (Fig. 66 III), and a zygote (e) is formed. The male gametes which do not conjugate may germinate, but the plants derived from them are much weaker than those produced by the zygotes. Strongly pronounced sexual differences are found in the Cutleriaceæ, in which order the male and female gametes arise in separate gametangia (Fig. 67 A). The male gametes (Fig. 67 D) are much smaller than the female gamete (Fig. 67 C); the latter, after swarming for a short time, withdraws the cilia, and is then ready to become fertilised (Fig. 67 B, E), thus we have here a distinct transition to the oogamous fertilisation which is found in the Fucaceæ. Alternation of generations is rarely found.

1. Sub-Family. =Zoogonicæ.=

Reproduction by means of gametes and zoospores.

Order 1. =Ectocarpaceæ.= The thallus consists of single or branched filaments with intercalary growth, extending vertically from a horizontal, branched filament or a disc, but sometimes it is reduced to this basal portion only. Zoosporangia and gametangia (for fertilisation see Fig. 66) are either outgrowths or arise by the transformation of one or several of the ordinary cells. The most common genera are: Ectocarpus and Pylaiella.

Order 2. =Choristocarpaceæ.= Choristocarpus, Discosporangium.

Order 3. =Sphacelariaceæ.= The thallus consists of small, parenchymatous, more or less ramified shoots, presenting a feather-like appearance. In the shoots, which grow by means of an apical cell (Fig. 68 S), a cortical layer, surrounding a row of central cells, is present. Sporangia and gametangia are outgrowths from the main stem or its branches. Sphacelaria, Chætopteris are common forms.

Order 4. =Encoeliaceæ.= Punctaria, Asperococcus, Phyllitis fascia.

Order 5. =Striariaceæ.= Striaria, Phlœospora.

Order 6. =Dictyosiphonaceæ.= Dictyosiphon.

Order 7. =Desmarestiaceæ.= Desmarestia aculeata is common.

Order 8. =Myriotrichiaceæ.= Myriotrichia.

Order 9. =Elachistaceæ.= Elachista fucicola is a common epiphyte on species of Fucus.

Order 10. =Chordariaceæ.= The shoot-systems are often surrounded by mucilage. Chordaria; Leathesia difformis occurs as rounded, brown-green masses of the size of a nut, generally attached to other Seaweeds.

Order 11. =Stilophoraceæ.= Stilophora rhizodes is common.

Order 12. =Spermatochnaceæ.= Spermatochnus paradoxus is common.

Order 13. =Sporochnaceæ.= Sporochnus.

Order 14. =Ralfsiaceæ.= Ralfsia verrucosa is common as a red-brown incrustation on stones and rocks at the water’s edge.

Order 15. =Lithodermataceæ.= Some species of the genus Lithoderma occur in fresh water.

Order 16. =Laminariaceæ.= The thallus is more or less leathery, and has generally a root-like lower part (Fig. 69) which serves to attach it, and a stalk or stem-like part, terminated by a large leaf-like expansion. Meristematic cells are situated at the base of the leaf, and from these the new leaves are derived. The older leaf thus pushed away by the intercalary formation of the younger ones, soon withers (Fig. 69). Gametes are wanting. Zoosporangia are developed from the lower part of a simple, few-celled sporangiophore, which is an outgrowth from a surface-cell and has a large club-formed apical cell. The sporangia are aggregated into closely packed sori, which cover the lower part of the terminal leaf, or occur on special, smaller, lateral, fertile fronds (Alaria). Most of the species belonging to this order live in seas of moderate or cold temperature and occur in the most northern regions that have yet been explored, forming their organs of reproduction during the cold and darkness of the arctic night. Laminaria is destitute of a midrib and has only one terminal leaf. L. digitata has a broad leaf, which, by the violence of the waves, is torn into a number of palmate strips (Fig. 69). L. saccharina has a small, undivided leaf. Alaria has a midrib and special fertile fronds. A. esculenta occurs plentifully on the west coast of Norway and on the shores of Great Britain. Chorda filum, a common seaweed, is thick, unbranched, and attains a length of several metres, without any strong demarcation between stalk and leaf. Some attain quite a gigantic size, e.g. Macrocystis pyrifera, whose thallus is said sometimes to be more than 300 metres in length. The Lessonia-species, like the above, form submarine forests of seaweed on the south and south-west coasts of South America, the Cape, and other localities in the Southern Hemisphere.

USES. The large Laminarias, where they occur in great numbers, are, like the Fuci, used for various purposes, for example, in the production of iodine and soda, and as an article of food (Laminaria saccharina, Alaria esculenta, etc.). Laminaria saccharina contains a large quantity of sugar (mannit) and is in some districts used in the preparation of a kind of syrup; in surgical operations it is employed for the distension of apertures and passages, as for instance the ear-passage. It is by reason of the anatomical peculiarities and structure of the cell-walls, that they are employed for this purpose. The cell-walls are divided into two layers, an inner one which has very little power of swelling, and an outer one, well developed and almost gelatinous--the so-called “intercellular substance”--which shrivels up when dried, but can absorb water and swell to about five times its size. The stalks of Laminaria clustoni are officinal.

Order 17. =Cutleriaceæ.= The thallus is formed by the union of the originally free, band-shaped shoots. The growth is intercalary. Sexual reproduction by the conjugation of male and female gametes. An asexual generation of different appearance, which produces zoospores, arises from the germination of the zygote. Cutleria, Zanardinia.

Sub-Family 2. =Acinetæ.=

Branched, simple cell-rows with intercalary growth. The organs of reproduction are partly uni-and partly multicellular; in the unicellular ones a cell without cilia is formed, which may be destitute of a cell-wall, but has one nucleus (oosphere?), or which has a cell-wall and contains several (generally four) nuclei (aplanospores?); in the multicellular, monosymmetric swarm-cells with two cilia (spermatozoids?) are formed. The fertilisation has not been observed.

Order 1. =Tilopteridaceæ.= Haplospora, Tilopteris.

Family 2. =Cyclosporeæ.=

The individuals are multicellular, with growth by an apical cell. The thallus--often bilateral--is differentiated into a root-like structure (attachment-disc), and stem, sometimes also into leaves (Sargassum). Sometimes a differentiation occurs into various tissue-systems, viz. an external assimilating tissue, a storing tissue, a mechanical tissue of thickened, longitudinal, parenchymatous, strengthening cells, and a conducting tissue of sieve-cells, or of short sieve-tubes with perforated walls. Colouring material, as in Phæosporeæ. Vegetative reproduction can only take place by means of detached portions of the thallus (Sargassum), which are kept floating by means of bladders (Fig. 70 A, a, Fig. 72). Zoospores are wanting.

The sexual reproduction takes place by oogamous fertilisation. The oogonia and antheridia are formed inside special organs (conceptacles), and are surrounded by paraphyses. The conceptacles (Fig. 70 B, Fig. 71 b) are small, pear-shaped or spherical depressions, produced by a special ingrowth of the surface cells of the thallus, and their mouths (ostioles) project like small warts; they are either situated near the end of the ordinary branches of the thallus (Fucus serratus, Fig. 71 a) which may be swollen on this account (Fucus vesiculosus, Fig. 70 A, b), or on special short branches (Ascophyllum, Sargassum). The vertical section of a conceptacle is seen in Fig. 70 B (see also Fig. 71 b) where, in addition to the paraphyses, oogonia only are seen (F. vesiculosus is diœcious--male plant, yellow-brown; female plant, olive-brown); but in some species antheridia, together with oogonia, are produced in the same conceptacle. The oogonia are large, almost spherical cells, situated on a short stalk, in each of which are formed from 1–8 (in Fucus, 8; in Ascophyllum, 4; in Halidrys, 1; in Pelvetia, 2) rounded, immotile oospheres. The wall of the oogonium ruptures, and the oospheres, still enclosed in the inner membrane, are ejected through the mouth of the conceptacle, and float about in the water, being finally set free by the bursting of the inner membrane. The antheridia are oblong cells (Fig. 70 C, a), many of which are produced on the same branched antheridiophore (Fig. 70 C); the numerous spermatozoids are provided with 2 cilia and are very small (Fig. 70 D, two antheridia surrounded by spermatozoids, one being open). The spermatozoids, still enclosed by the inner membrane of the antheridium, are similarly set free, and fertilisation takes place in the water, numerous spermatozoids collecting round the oosphere (Fig. 70 E), which is many times larger, and by their own motion causing it to rotate. After fertilisation, the oospore surrounds itself with a cell-wall and germinates immediately, attaching itself (Fig. 70 F) to some object, and by cell-division grows into a new plant.

Order 1. =Fucaceæ.= The following species are common on our coasts: Fucus vesiculosus (Fig. 70) has a thallus with an entire margin, and with bladders arranged in pairs; F. serratus (Fig. 71) without bladders, but with serrated margin; Ascophyllum nodosum has strap-like shoots, which here and there are swollen to form bladders; Halidrys siliquosa has its swimming bladders divided by transverse walls; Himanthalia lorea, which is found on the west coast of Norway, and the south coast of England, has a small perennial, button-shaped part, from the centre of which proceeds the long and sparsely branched, strap-like, annual shoot, which bears the conceptacles. The Gulf-weed (Sargassum bacciferum, Fig. 72) is well known historically from the voyage of Columbus; it is met with in large, floating, detached masses in all oceans, and is found most abundantly in the Atlantic, off the Canary Islands and the Azores, and towards the Bermudas. The stalked, spherical air-bladders are the characteristic feature of this genus. The thallus is more highly developed than in Fucus, and there is a contrast between the stem and leaf-like parts. The portions which are found floating are always barren, only those attached are fertile.

USES. The Fucaceæ, like the Laminariaceæ, are used as manure (the best kinds being Fucus vesiculosus and Ascophyllum nodosum), for burning to produce kelp, and as food for domestic animals (Ascophyllum nodosum is especially used for this purpose).

Class 9. =Dictyotales.=

The plants in this class are multicellular, and brown, with apical growth, new cells being derived either from a flat apical cell, or from a border of apical cells. The thallus is flat, leaf- or strap-shaped, attached by haptera, which are either found only at the base, or on the whole of the lower expansion of the thallus. The cells are differentiated into the following systems of tissues: an external, small-celled layer of assimilating cells, generally one cell in thickness, and an internal, large-celled layer of one or only a few cells in thickness, forming the mechanical and conducting tissues. All the reproductive cells are motionless. Asexual reproduction by naked, motionless spores (tetraspores) which are formed 1–4 in each tetrasporangium, the latter being outgrowths from the surface cells of special, sexless individuals. Zoospores are wanting. The sexual organs are of two kinds, oogonia and antheridia, which are formed from the surface cells, either on the same or different individuals. The oogonia are spherical or oval, and are generally placed close together; each contains one oosphere, which on maturity is ejected into the surrounding water, and is then naked and motionless. The antheridia are formed of longitudinal cells, united in groups, whose contents by repeated divisions--transverse and longitudinal--are divided into a large number of small, colourless, motionless spermatia--round or elongated--which are set free by the dissolution of the wall of the antheridium. The process of fertilisation has not yet been observed.

The Dictyotales, in having tetraspores and spermatia, deviate considerably from the Phæophyceæ, but may be classed near to the Tilopteridæ, in which there are asexual spores with 4 cell-nuclei, which may be considered as an indication of the formation of tetraspores.

Order 1. =Dictyotaceæ.= Dictyota dichotoma which has a thin, regularly dichotomously divided thallus, occurs on the coasts of the British Isles. Padina is found on the south coast.

Class 10. =Rhodophyceæ (Red Seaweeds).=

The plants comprised in this class are multicellular; they are simple or branched filaments, or expansions consisting of 1 to several layers of cells; the thallus may be differentiated (as in many Florideæ), to resemble stem, root, and leaf. The cells contain a distinctly differentiated nucleus (sometimes several), and distinct chromatophores, coloured by rhodophyll. The chlorophyll of the chromatophores is generally masked by a red colouring matter (phycoerythrin), which may be extracted in cold, fresh water; or rarely by phycocyan. Pyrenoids occur in some. Starch is never formed in the chromatophores themselves, but a modification--Florideæ starch--may be found in the colourless protoplasm. Asexual reproduction by motile or motionless spores (tetraspores) which are devoid of cilia and of cell-wall. Swarmspores are never found.

Sexual reproduction is wanting, or takes place by the coalescence of a spermatium and a more or less developed female cell. The spermatia are naked masses of protoplasm, devoid of cilia and chromatophores. The female cell (carpogonium) is enclosed by a cell-wall, and after fertilisation forms a number of spores, either with or without cell-walls (carpospores), which grow into new individuals.

The Rhodophyceæ may be divided into two families:

1. BANGIOIDEÆ. 2. FLORIDEÆ.

Family 1. =Bangioideæ.=

The thallus consists of a branched or unbranched cell-filament, formed of a single row or of many rows of cells, or of an expansion, one or two layers of cells in thickness, but without conspicuous pores for the intercommunication of the cells. The growth of the thallus is chiefly intercalary. The star-like chromatophores contain chlorophyll and are coloured blue-green with phycocyan, or reddish with phycoerythrin; all these colouring matters are occasionally found in the same cell (Bangia-species). Asexual reproduction by tetraspores, without cilia, but capable of amœboid movements.

Sexual reproduction is wanting, or takes place by the coalescence of a spermatium with a carpogonium, which is only slightly differentiated from the vegetative cells, and is devoid of a trichogyne. The carpospores are destitute of cell-wall and arise directly by the division of the fertilised oosphere. The Bangioideæ occur chiefly in salt water.

Order 1. =Goniotrichaceæ.=--The thallus consists of a branched cell-filament without rhizoids. Tetraspores are formed directly from the entire contents of the mother-cell, without any preceding division. Fertilisation unknown. Asterocystis, Goniotrichum.

The Goniotrichaceæ, through the blue-green Asterocystis, are allied to the Myxophyceæ, and through Goniotrichum to the Porphyraceæ.

Order 2. =Porphyraceæ.=--The thallus is formed of an expansion consisting of a layer of 1–2 cells, which, at the base, are attached to the substratum by means of a special form of haptera (Porphyra, Diploderma); or of unbranched (very rarely slightly branched) filaments, attached at the base by haptera (Bangia): or it extends from a prostrate cell-disc (various species of Erythrotrichia). Tetraspores are formed after one or more divisions of the mother-cell, either from the whole or only a part of its contents; they possess amœboid movements, or have a jerky, sliding-forward motion. The antheridia have the same appearance as the vegetative cells, but divide several times, and several spermatia are formed, either simultaneously from the whole contents (Porphyra, Bangia), or the spermatia are successively formed from a part of the contents of the antheridium (Erythrotrichia). The carpogonium is without a trichogyne, but the oosphere has a colourless spot which may sometimes rise a little above the surface of the thallus, and may be considered as an early stage in the development of the trichogyne. The spermatia form a canal through the membrane of the carpogonium, and their contents coalesce with the oosphere at its colourless spot. The fertilised oosphere divides on germination into a number of carpospores, which are set free as naked, motionless masses of protoplasm, which grow and give rise to new individuals (alternation of generations).

Family 2. =Florideæ.=

The thallus has one or more apical cells, grows principally by apical growth, and may be differentiated into root, stem, and leaf. The chromatophores vary in form, but have a red or brownish colour, due to chlorophyll and phycoerythrin. Asexual reproduction by motionless tetraspores, which generally arise by the division into four of the contents of the tetrasporangium. The carpogonium has a trichogyne, and the carpospores, which are formed indirectly from the fertilised oosphere, possess a cell-wall.

The thallus may assume very different forms. In the simplest species it is filamentous and formed of single, branched rows of cells (Callithamnion, etc., Fig. 73). Ceramium has a filamentous thallus, generally dichotomously forked (Fig. 75), or sometimes pinnately branched, which, at the nodes, or throughout its entire length, is covered by a layer of small cortical cells. Polysiphonia (Fig. 74) has a filamentous, much branched thallus, made up of a central cylindrical cell, surrounded by a layer of other cells, cortical cells, which in length and position correspond to the central ones. In many of the Red Algæ the vegetative organs are differentiated into stems and leaves, the former having, as in Chara, unlimited growth in length, whilst the latter soon attain their full development. Chondrus has a fleshy, gelatinous thallus, without nodes; it is repeatedly forked into flat branches of varying thickness. Furcellaria has a forked thallus with thick branches and without nodes. The thallus of Delesseria (Fig. 76) consists of branches, often bearing leaf-like structures, with a midrib and lateral ribs springing from it. These ribs persist through the winter, and at the commencement of the succeeding period of vegetation the lateral ribs become the starting points for new leaves. In Corallina the thallus is pinnately branched, and divided into nodes and internodes. The name has been given to this genus from the fact that the thallus is incrusted with carbonate of lime to such a degree that it becomes very hard, and the whole plant adopts a coral-like appearance. Other genera which are similarly incrusted, and have a leaf-like or even crustaceous thallus (such as Melobesia, Lithothamnion), are included in this family.

In some instances the cells of the thallus may be found differentiated into more or less well defined tissues, so that it is possible to find special assimilating, mechanical, and conducting tissues, the last named in some cases having the double function of conducting and of serving as a reservoir in which starch is found as a reserve material. The cells of the Florideæ, which are formed by the division of a mother-cell into two daughter-cells of unequal size, have always larger or smaller pits in the cell-walls, and the thin cell-wall separating two pits from each other is perforated by a number of small holes. These pits are particularly developed in the conducting tissues, but sieve-tubes are very rarely to be found.

Tetraspores may be wanting (e.g. Lemanea) or may often arise on special, non-sexual individuals. In some (e.g. Batrachospermum) only one tetraspore is formed in each tetrasporangium, but the number is generally four, which may be formed tetrahedrally (Fig. 73) or by divisional walls perpendicular to each other, or even in a single row. The tetrasporangia in some species are free (Fig. 73), but in the majority they are embedded in the thallus.

The sexual reproduction (discovered by Thuret and Bornet, 1867) differs in the essential points from that of all other plants, and approaches most nearly to the sexual reproduction of the Bangioideæ. The sexual cells are developed from the terminal cells (never nodal cells) of the branched cell-filaments, which constitute the thallus. The mother-cells of the spermatia (spermatangia) are generally arranged in a group, in the so-called antheridia (Figs. 74, 77 A, a). On becoming ripe the membrane of the spermatangium ruptures and the spermatia emerge as spherical or ovoid, naked (a little later they may possess a cell-wall) masses of protoplasm which are not endowed with the power of motion, and hence are carried passively by the current of the water in which they may happen to be, to the female cell. This latter is analogous with the oogonium of the Green Algæ. The female reproductive organ is termed the procarpium, and consists of two parts, a lower swollen portion--the carpogonium (Fig. 77 b in A and B)--which contains the cell-nucleus, and an upper filamentous prolongation--the trichogyne (Fig. 77 B)--which is homologous with the colourless receptive spot of the oosphere of the Green Algæ, and the Porphyraceæ. In the sexual reproduction of the majority of the Florideæ, a very important part is played by certain special cells, rich in cell-contents--the auxiliary cells. These are either dispersed in the interior of the thallus, or are arranged together in pairs with the cell-filament which bears the carpogonium, and are generally united with this to form an independent multicellular procarpium. The spermatia attach themselves firmly to the trichogyne and surround themselves with a cell-wall. The dividing wall at the point of contact is perforated, and the nucleus of the spermatium probably travels through the trichogyne to the swollen part of the procarpium--the carpogonium--and fuses with its nucleus. After fertilisation the trichogyne withers (Fig. 77 C), but the lower portion of the procarpium, constituting the fertilised oosphere, grows out and forms in various ways, first a tuft of spore-forming filaments known as gonimoblasts, and finally the carpospores. These latter form a new asexual generation (compare the germination of the oospore of Œdogonium and Coleochæte).

The gonimoblasts may arise in three ways:--

1. In the Nemalionales, branched filaments grow out from the oosphere and form an upright, compressed or expanded tuft of spore-forming filaments.

2. In the Cryptonemiales, several branched or unbranched filaments (ooblastema-filaments) grow out from the oosphere, and conjugate in various ways with the auxiliary cells. The gonimoblasts are then formed from the single cells produced by the conjugation.

3. In the Gigartinales and Rhodymeniales the oosphere conjugates with an auxiliary cell by means of a short ooblastema-filament, and from this auxiliary cell a gonimoblast is produced.

The motionless carpospores, which sometimes in the early stages are naked, and afterwards invested with a cell-wall, are developed from the terminal cells (and perhaps also from some of the other cells) of the branches of the gonimoblast. The gonimoblasts constitute sharply defined parts of the plant in which the carpospores arise. These parts are called cystocarps and are either naked (Fig. 77 E), or surrounded by a covering (pericarp or involucre, Fig. 77 A) formed in different ways. On this account the Florideæ were formerly divided into GYMNOSPOREÆ (Batrachospermum, Nemalion, Ceramium, etc.) and ANGIOSPOREÆ (Farcellaria, Lejolisia, Delesseria, Melobesia, etc.).

The Florideæ are divided into four sub-families:--

Sub-Family 1. =Nemalionales.= The fertilised oosphere produces directly the gonimoblast.

Order 1. =Lemaneaceæ.= Algæ of brownish colour and living in fresh water. They lack tetraspores, and the very sparingly branched fertile filaments, composed of many rows of cells, grow out from a proembryo, which consists of a single row of cells bearing branches. Lemanea fluviatilis, often found on rocks and stones in quickly flowing streams.

Order 2. =Helminthocladiaceæ.= Tetraspores are generally wanting (e.g. in Nemalion) or arise one in each tetrasporangium (e.g. Batrachospermum) and it is only in Liagora that four cruciate tetraspores are formed. Chantransia corymbifera consists of simple, branched cell-rows, and is an independent species. Several other Chantransia-forms, living in fresh water, are “proembryos” of species of the genus Batrachospermum. The germinating carpospore grows out into filaments and forms a so-called proembryo which, if not shaded, attains only a small size, but when growing in shady situations presents a much greater development. These highly developed proembryos have been described as species of Chantransia. The proembryo can reproduce by division, or by tetraspores which are developed singly in the sporangia; in B. vagum and B. sporulans which do not possess fully developed female reproductive organs, the proembryos serve almost entirely to reproduce the species. The young Batrachospermum-plant arises from the end of an upright filament of the proembryo. The proembryo is generally persistent, and continually produces new Batrachospermums. These latter bear the sexual reproductive organs and also whorls of branches: the central row of cells is enclosed by cells growing from the base of the whorls of branches, and from these cortical cells secondary proembryos are developed. In this alternation of shoots there is really no alternation of generations, since the proembryo and the shoots with the sexual reproductive organs are parts of the same thallus.

Several species of Batrachospermum have a bluish green or verdigris colour. Nemalion multifidum has a brown-red thallus, slightly branched, which is attached to rocks near the water’s edge.

Order 3. =Chætangiaceæ.= Galaxaura has a thallus thickly incrusted with lime.

Order 4. =Gelidiaceæ.= Naccaria, Gelidium.

Sub-Family 2. =Gigartinales.= The fertilised auxiliary cell grows towards the thallus, to produce the gonimoblasts. Procarpia generally present.

Order 5. =Acrotylaceæ.= Acrotylus.

Order 6. =Gigartinaceæ.= Gigartina, Phyllophora, Ahnfeltia; Chondrus crispus, with dark red, dichotomously branched thallus, is common on the coasts of Scandinavia and Great Britain.

Order 7. =Rhodophyllidaceæ.= Rhodophyllis, Euthora; Cystoclonium purpurascens is common, and sometimes the ends of its branches may be modified into tendril-like haptera.

Sub-Family 3. =Rhodymeniales.= The fertilised auxiliary cell forms the gonimoblast on the side away from the thallus. Procarpia are abundantly produced.

Order 8. =Sphærococcaceæ.= Gracilaria.

Order 9. =Rhodymeniaceæ.= Rhodymenia palmata is a common species. Lomentaria, Chylocladia, Plocamium.

Order 10. =Delesseriaceæ.= Delesseria sanguinea; D. alata and D. sinuosa are handsome forms which are not uncommon.

Order 11. =Bonnemaisoniaceæ.= Bonnemaisonia.

Order 12. =Rhodomelaceæ.= Rhodomela, Odonthalia; Polysiphonia, of which many species are to be found on the coasts of Great Britain, has a filamentous, richly branched thallus consisting of a central row of cells surrounded by a varying number of cortical cells of similar size--the so-called “siphons.”

Order 13. =Ceramiaceæ.= Pretty Algæ, often branched dichotomously, or unilaterally pinnate. Spermothamnion, Griffithsia, Callithamnion, Ceramium, Ptilota.

Sub-Family 4. =Cryptonemiales.= The cells formed by the coalescence of the auxiliary cells and the ooblastema-filaments, produce the gonimoblasts. The carpogonium-filaments and the auxiliary cells are scattered singly in the thallus.

Order 14. =Gloiosiphoniaceæ.= Gloiopeltis.

Order 15. =Grateloupiaceæ.= Halymenia, Cryptonemia.

Order 16. =Dumontiaceæ.= Dumontia, Dudresnaya.

Order 17. =Nemastomaceæ.= Furcellaria, which has dichotomously branched, round shoots, is common on the coasts of Great Britain.

Order 18. =Rhizophyllidaceæ.= Polyides, Rhizophyllis.

Order 19. =Squamariaceæ.= The Algæ belonging to this order form crust-like coverings on stones, mussel-shells, and on other Algæ, but are not themselves incrustated: Petrocelis, Cruoria, Peyssonellia.

Order 20. =Corallinaceæ.= Partly crustaceous, partly erect, branched Algæ, thickly incrusted with lime, so that a few species (Lithothamnia, also called Nullipora) occur in fossilized condition from Jurassic to Tertiary periods. Melobesia, Lithophyllum, Lithothamnion, Corallina.

USES. “Carragen” is the thallus of Chondrus crispus (Irish Moss) and Gigartina mamillosa. It is a common article of food on the coasts of Ireland, and swells to a jelly when cooked. It is officinal. Rhodymenia palmata is generally eaten as food in Ireland and in some places on the west coast of Norway; it is also used as food for sheep and hence is termed “Sheep-seaweed.” Agar-Agar is the jelly obtained from species of Gelidium and Gigartina growing in China and Japan.

Sub-Division III. =FUNGI.=

=Mode of Life.= The Fungi have no chlorophyll, and are thus unable in any stage of their existence to assimilate carbon; they must therefore live as saprophytes or parasites. There is, however, no strong line of demarcation between these; many Fungi commence as true parasites, but only attain their full development upon or in dead plants or animals (Rhytisma, Empusa). Many saprophytes may occasionally appear as parasites, and are then designated “facultative parasites” (Nectria cinnabarina, Lophodermium pinastri), in contradistinction to those which only appear as parasites, “obligate parasites” (Mildew, Brand-and Rust-Fungi, Cordyceps).

The parasites which live on the surface of the host-plant are termed epiphytic (Mildew, Fusicladium); and those living in its tissues are termed endophytic (Ustilago, Peronospora). Epizoic (Oidium tonsurans, Laboulbenia) and endozoic Fungi (Cordyceps, Entomophthora), are distinguished, in the same manner, as those which live on the surface or in the interior of animals. The Fungi designated pathogenic are especially those which produce disease in human beings and in animals.

Most of the diseases of plants are attributed to the parasitic Fungi. These force their way into the host-plant by piercing the outer wall of the epidermis, as in the Potato-disease; or by growing in through the stomata, e.g. the summer generations of the Rust of Wheat; or they can only penetrate through a wound, e.g. Nectria. Some effect an entrance into the host-plant by the secretion of a poisonous matter or ferment, which softens and destroys the cell-walls (Sclerotinia). Some Yeast and Mould Fungi secrete ferments (enzymes), which, for example, convert cane-sugar into a sugar capable of fermentation.

The relation of the parasitic Fungus to the host-plant is mainly of two kinds. In the one case, the cell-contents are destroyed, the protoplasm is killed, and the cellular tissue becomes discoloured and dies (Peronospora, Armillaria mellea, Polyporus); in the other case, the parasite has an irritating effect on the cellular tissue, whereby the affected organ grows more rapidly and becomes larger than normal, producing hypertrophy. Such malformations are termed Fungi-galls (Mycocecidia); in this manner “witches’ brooms” are produced by Æcidium, “pocket-plum” by Taphrina, and other deformities by Exobasidium and Cystopus candidus. This hypertrophy may either be produced by a vigorous cell-multiplication, which is most frequently the case, or by the enlargement of the individual cells (Synchytrium, Calyptospora). The relation between host and Fungus among the Lichens is of a very peculiar nature, termed “symbiosis.”

=Vegetative Organs.= The vegetative parts of a Fungus are termed its mycelium.[10] This is formed of a mass of long, cylindrical, branched cells resembling threads (and hence termed hyphæ), which have a continued apical growth. The mycelium, in its early development, shows a well-marked difference between the two main groups of true Fungi: in the Phycomycetes, or Algal Fungi, the mycelium has no transverse walls, and is therefore unicellular, while in the Mesomycetes and Mycomycetes it is provided with dividing walls, which gradually arise during growth, in the youngest hyphæ; intercalary transverse walls may also be formed at a later period. In the hyphæ of some of the Higher Fungi (Hymenomycetes), connections may be formed between two contiguous cells of the same hypha, by a protuberance growing out from an upper cell just above the transverse wall, and forming a junction with the cell below. These are known as clamp-connections; they appear to be of use in affording communication between the two cells.

The hyphæ of Fungi, where they come in contact with one another, often grow together, so that =H=-formed combinations (fusions) are produced, which give rise to very compact felted tissue. When the hyphæ are not only closely interwoven, but also united and provided with many transverse walls, the mycelium assumes the appearance of a tissue with isodiametric cells, and is then termed pseudo-parenchyma. The hyphæ-walls are sometimes very much thickened, and composed of several layers, and the external layers, by the absorption of water, may often swell very much and become mucilaginous. In some instances the walls are colourless, in others coloured, the most frequent colour being brown. The cell-contents may also be coloured, and in that case are generally yellow; this colour is chiefly connected with the fat (oil) which may be found in abundance in the Fungi, whilst starch is invariably absent in all the true Fungi.

The mycelium assumes many different forms; sometimes it appears as a thread-like, cobwebby, loose tissue, less frequently as firm strands, thin or thick membranes, horn-like plates or tuber-like bodies. The thread-like mycelium may, in the parasitic Fungi, be intercellular or intracellular, according as it only extends into the interstices between the cells or enters into the cells proper. In the first case there are generally found haustoria, or organs of suction (e.g. among the Peronosporaceæ; Taphrina, on the contrary, has no haustoria); but haustoria are also found among the epiphytic Fungi (e.g. Erysiphaceæ). Intracellular mycelia are found in the Rust-Fungi, in Claviceps purpurea, Entomophthora, etc. In spite of its delicate structure, this mycelium may live a long time, owing to the circumstance that it continues to grow peripherally, while the older parts gradually die off (“fairy rings”).

String-like mycelia may be found, for example, in Phallus, Coprinus, and are formed of hyphæ, which run more or less parallel to each other. Membrane-like mycelia are chiefly to be found in Fungi growing on tree-stems (Polyporaceæ and Agaricaceæ); they may have a thickness varying from that of the finest tissue-paper to that of thick leather, and may extend for several feet. The peculiar horny or leather-like strands and plates which, for instance, appear in Armillaria mellea, are known as Rhizomorpha; they may attain a length of more than fifty feet. The tuber-like mycelia or sclerotia play the part of resting mycelia, since a store of nourishment is accumulated in them, and after a period of rest they develope organs of reproduction. The sclerotia are hard, spherical, or irregular bodies, from the size of a cabbage seed to that of a hand, internally white or greyish, with a brown or black, pseudo-parenchymatous, external layer. Sclerotia only occur in the higher Fungi, and are found both in saprophytes, e.g. Coprinus, and in parasites, e.g. Claviceps (Ergot), Sclerotinia.

=Reproduction.= SEXUAL REPRODUCTION is found only among the lower Fungi which stand near to the Algæ, the Algal-Fungi, and takes place by the same two methods as in the Algæ, namely by conjugation and by the fertilisation of the egg-cell in the oogonium.

The majority of Fungi have only ASEXUAL reproduction. The most important methods of this kind of reproduction are the sporangio-fructification and the conidio-fructification.

In the SPORANGIO-FRUCTIFICATION the spores (endospores) arise inside a mother-cell, the sporangium (Fig. 80). Spores without a cell-wall, which move in water by means of cilia and hence are known as swarmspores or zoospores, are found among the Oomycetes, the sporangia in which these are produced being called swarm-sporangia or zoosporangia (Figs. 86, 87, 91, 94).

In the CONIDIO-FRUCTIFICATION the conidia (exospores) arise on special hyphæ (conidiophores), or directly from the mycelium. When conidiophores are present, the conidia are developed upon them terminally or laterally, either in a basipetal succession (in many Fungi, for example in Penicillium, Fig. 111, Erysiphe, Cystopus), or acropetally (in which method the chains of conidia are often branched; examples, Pleospora vulgaris, Hormodendron cladosporioides). All conidia are at first unicellular, sometimes at a later stage they become two-celled or multicellular through the formation of partition-walls (Piptocephalis). The conidia with thick, brown cell-walls, and contents rich in fats (resting conidia), can withstand unfavourable external conditions for a much longer period than conidia with thin walls and poor in contents.

The SPORANGIA arise either from the ordinary cells of the mycelium (Protomyces), or are borne on special hyphæ. They are generally spherical (Mucor, Fig. 80; Saprolegniaceæ), egg-, pear-, or club-shaped (Ascomycetes), more rarely they are cylindrical or spindle-shaped. While among the Phycomycetes the size, form, and number of spores are indefinite in each species, in the Ascomycetes the sporangia (asci) have a definite size, form, and number of spores. The spores of the Ascomycetes are known as ascospores.

The sporangio-fructification is found under three main forms.

1. FREE SPORANGIOPHORES which are either single (Mucor, Fig. 78), or branched (Thamnidium).

2. SPORANGIAL-LAYERS. These are produced by a number of sessile or shortly-stalked sporangia, being formed close together like a palisade (Taphrina, Fig. 105).

3. SPORANGIOCARPS. These consist usually of many sporangia enclosed in a covering, they are found only in the Carpoasci, and are also known as ascocarps. The parts of an ascocarp are the covering (peridium), and the hymenium, which is in contact with the inner wall of the peridium, and is generally made up of asci, and sterile, slender hyphæ. The latter either penetrate between the asci and are branched and multicellular (paraphyses, Figs. 103 d, 123, 125, 129), or clothe those parts of the inner wall which bear no asci (periphyses; among many peronocarpic Ascomycetes, e.g. Chætomium, Sordaria, Stictosphæra hoffmanni). The ascocarps are produced directly from the mycelium, or from a stroma, that is a vegetative body of various forms, in which they may be embedded (Figs. 116 B, C).

Among the conidio-fructifications there are, in the same way, three divisions.

1. FREE CONIDIOPHORES (Fig. 109). The form of the conidiophores, the shape, and number of its spores are various. In the most highly developed Fungi, the Basidiomycetes, there are, however, special more highly developed conidiophores, the basidia, which have a definite form and spores of a definite shape and number. The conidia borne on basidia are called basidiospores.

2. CONIDIAL-LAYERS. (a) The SIMPLEST case of this is found when the conidiophores arise directly from the mycelium, parallel to one another, and form a flat body (e.g. Exobasidium vaccinii, Hypochnus; among the Phycomycetes, Empusa muscæ and Cystopus). (b) In a HIGHER form the conidial-layers are thick, felted threads (stroma) inserted between the mycelium and the hymenium (i.e. the region of the conidiophores). Examples are found in a section of the Pyrenomycetes (Fig. 122). (c) The HIGHEST form has the basidial-layer, that is a conidial-layer with more highly developed conidiophores (basidia). The basidial-layer, with stroma, and the hymenium (region of the basidia), forms the basidio-fructification, which is branched in the Clavariaceæ, and hat-shaped in other Hymenomycetes (in these groups the hymenium is confined to the lower side of the pileus).

The hymenium of the conidial-layer and basidial-layer is composed entirely of conidiophores, or of conidiophores and sterile hyphæ (paraphyses) which are probably always unicellular. Paraphyses are found in Entomophthora radicans, and in certain Basidiomycetes (e.g. Corticium).

3. CONIDIOCARPS (pycnidia). A special covering surrounds the conidia-forming elements. The inner side of this covering (peridium) bears the hymenium, i.e. those elements from which the conidia are abstricted. The conidiocarps arise either immediately from the hyphæ or from a stroma in which they are generally embedded. Conidiocarps are entirely wanting in the Phycomycetes. On the other hand they are found among the Ascomycetes and Basidiomycetes, and in the latter group the conidiocarps contain more highly differentiated conidiophores (basidia) and are known as basidiocarps. Conidiocarps with simple conidiophores, are found only among the Basidiomycetes, in the Uredinaceæ, and in Craterocolla cerasi. In the Ascomycetes (Figs. 120 d, e; 117 a, b; 123 a; 124 b) the conidiocarps are visible, as points, to the naked eye, while the basidiocarps of the Basidiomycetes (Figs. 170, 171, 173–176, 178–180) vary from the size of a pea to that of a child’s head. The “spermogonia” of the Ascomycetes and Lichenes, are conidiocarps with small conidia (microconidia) which germinate sometimes more slowly than other conidia, and formerly were erroneously considered as male reproductive cells, and called spermatia.

The conidia of the Fungi are not primitive structures. The comparison of the sporangia and conidia among the Zygomycetes, and among the species of the genus Peronospora shows, that the conidia are aberrant formations, and that they have arisen through the degeneration of the sporangium, which, by the reduction of its spores to one, has itself become a spore.

In the genera Thamnidium and Chætocladium the gradual diminution of the sporangia, and the reduction of the number of spores can be distinctly followed. In Thamnidium the number of spores is often reduced to one, which is free in the sporangium. In Chætocladium however the sporangia are typically one-spored, the spore is always united with the sporangium, and the two become a single body, the so-called conidium, which is in reality a closed sporangium. How close is the connection between the sporangia and conidia of Thamnidium and Chætocladium, is seen from the fact that, in the conidial stage of Chætocladium the same whorl-form of branching appears as in the sporangial stages of Thamnidium chætocladioides, and also, that the conidia of Ch. fresenianum throw off the former sporangium-wall (exosporium), while Ch. jonesii germinates without shedding its exosporium. The Phycomycetes have doubtless sprung from Water-Algæ and inherit the sporangia from them. On this supposition, as the Phycomycetes assumed a terrestrial mode of life, the sporangia would become adapted to the distribution of the spores by means of the air, the sporangia would become small, contain dust-like spores, and would eventually become closed-sporangia, i.e. conidia. The conidia are a terrestrial method for the multiplication of Fungi. In the Hemiasci and the Ascomycetes the sporangia are still preserved, but in every instance they are adapted to terrestrial spore-distribution, their spores being set free on the destruction of the sporangium-wall (generally shot out) and distributed through the air. For further examples of spore-distribution see below, p. 91–93.

The reproduction of Fungi is accomplished not only by spores and conidia, but also sometimes by chlamydospores. These are fundaments[11] of sporangiophores and conidiophores, which have taken on a resting condition in the form of a spore, and are able to germinate and produce carpophores. In the formation of the chlamydospores the hyphæ accumulate reserve materials at the expense of the neighbouring cells; in the undivided hyphæ of the Phycomycetes transverse walls are formed, and finally the chlamydospores are set free by the decay of the empty cells connecting them with the mycelium. One must distinguish between oidia and true chlamydospores. The former are more simple, the latter are a somewhat more differentiated form of carpophore fundaments, which serve for propagation in the same manner as spores. In Chlamydomucor racemosus the chlamydospores grow out into the air and form differentiated carpophores. In the Autobasidiomycetes they only germinate vegetatively, and not with the formation of fructifications. From Chlamydomucor up to the Autobasidiomycetes the successive development of the fructification, which is interrupted by the formation of the chlamydospores, degenerates more and more. Among certain Ustilagineæ the chlamydospores (brand-spores) no longer germinate with the production of fructifications. In the Uredinaceæ, only one of the three chlamydospore-forms has the property of producing fructifications on germination; the other forms only germinate vegetatively, like ordinary spores, and in the same manner as the chlamydospores of the Autobasidiomycetes. In the Hemibasidii, and the Uredinaceæ, in Protomyces, the chlamydospores are the chief means of reproduction. They are found also among the Ascomycetes.

The sporangia and the conidia of the Fungi have their common origin in the sporangia of the Phycomycetes. The asci (and the Ascomycetes which are characterised by these bodies) are descended from the sporangia-forming, lower Fungi; the basidia (and the Basidiomycetes) from those which bear conidia. The sporangia of the Phycomycetes are the primitive form and the starting point for all the reproductive forms of the Fungi. The chlamydospores appear besides in all classes of Fungi as supplementary forms of reproduction, and are of no importance in determining relationships. Although the expression “fruit” must essentially be applied to true Phanerogams, yet, through usage, the term “fruit-forms,” is employed to designate the forms or means of reproduction of Fungi, and the organs of reproduction are known as organs of fructification, the sporangiophores and conidiophores as fruit-bearers (carpophores), and the sporangiocarps, conidiocarps, and basidiocarps as “fruit-bodies.”

The majority of Fungi have more than one method of reproduction, often on various hosts (Uredinaceæ). Species with one, two, or more than two methods of reproduction are spoken of as having monomorphic, dimorphic, or pleomorphic fructification. Monomorphic, e.g. the Tuberaceæ; dimorphic, Mucor, Piptocephalis, Saprolegniaceæ, Penicillium crustaceum; pleomorphic, Puccinia graminis, Capnodium salicinum (in the last species there are five methods of reproduction: yeast-like conidia, free conidiophores, conidiocarps with small and large conidia, and ascocarps).

=The liberation and distribution of the spores and conidia.= The spores and conidia, on account of their small size and lightness, are spread far and wide by currents in the air, but in addition to this method, insects and other animals frequently assist in disseminating them. The liberation of the conidia is occasionally effected by the complete shrinking away of the conidiophore, but more frequently by abstriction from the conidiophores, either by their gradually tapering to a point, or by the dissolution of a cross-wall (generally of a mucilaginous nature). The individual links of conidia-chains are detached from one another in the same way, or often by means of small, intercalary cells, which are formed at the base of the individual links, and becoming slimy, dissolve upon the maturity of the spores. Special contrivances for ejecting the spores and conidia may often be found. In Peronospora the cylindrical fruit-hyphæ in the dry condition become strap-shaped and also twisted. These are very hygroscopic, and the changes of form take place so suddenly, that the spores are violently detached and shot away. In Empusa a peculiar squirting mechanism may be found (Fig. 85). Each club-shaped hypha which projects from the body of the fly, bears a conidium at its apex; a vacuole, which grows gradually larger, is formed in the slimy contents of the hypha, and the pressure thereby eventually becomes so great that the hypha bursts at its apex, and the conidium is shot into the air. By a similar mechanism, the spores of many of the Agaricaceæ are cast away from the parent-plants. In the case of Pilobolus (Fig. 84) the entire sporangium is thrown for some distance into the air by a similar contrivance, the basal region of the sporangium having, by the absorption of water, been transformed into a slimy layer which is readily detached. Sphærobolus, a Gasteromycete, has a small, spherical fruit-body (basidiocarp), the covering of which, when ripe, suddenly bursts, and the basidiospores contained in it are forcibly ejected.

The spores which are enclosed in asci are, in some instances, set free from the mother-cell (ascus) prior to their complete development (Elaphomyces, Eurotium). In the case of the majority of the Pyrenomycetes and Truffles, the asci swell by the absorption of water into a slimy mass, which gradually disappears, so that the spores lie free in the fruit-body; they either remain there till the fruit-body decays, as in those which have no aperture (Perisporiaceæ, Tuberaceæ), or the slimy mass, by its growth, is forced out through the aperture of the sporocarp, taking the spores with it (Nectria). The ejection of the spores by mechanical means takes place in a number of Ascomycetes, and should many spores be simultaneously ejected, a dust-cloud may be seen with the naked eye to arise in the air from the fruit-body. This is the case in the larger species of Peziza, Helvella, Rhytisma, when suddenly exposed to a damp current of air. A distinction is drawn between a simultaneous ejection of all the spores contained in the ascus, and an ejection at intervals (successive), when only one spore at a time is thrown out. The first of these methods is the most frequent, and is brought about by the ascus being lined with a layer of protoplasm, which absorbs water to such a degree that the elastic walls are extended at times to double their original size. The spores are forced up against the free end of the ascus, a circular rupture is made at this point, and the elastic walls contract, so that the fluid with the spores is ejected. Special means may in some instances be found to keep the spores together, and compel their simultaneous ejection. Thus, a tough slime may surround all the spores (Saccobolus), or a chain-apparatus, similarly formed of tough slime; or there may be a hooked appendage from each end of the spores which hooks into the appendage of the next spore (Sordaria). The paraphyses occurring between the asci in many Ascomycetes, also play a part in the distribution of the spores, by reason of the pressure they exercise. The asci in some of the Pyrenomycetes, which are provided with jar-shaped fruit-bodies, elongate to such an extent that, without becoming detached from their bases, they reach the mouth of the fruit-body one at a time, burst and disperse their spores, and so make room for those succeeding. An ejection of the spores at intervals from the ascus is rarer. It takes place, for instance, in Pleospora, whose asci have a double wall. The external wall, by absorption of water, at last becomes ruptured, and the internal and more elastic membrane forces itself out in the course of a few seconds to one of two or three times greater length and thickness, so that one spore after another is forcibly ejected from a narrow aperture at the end of the ascus.

=Germination of spores= (conidia and chlamydospores). In many spores may be found one or more germ-pores, i.e. thinner places, either in the inner membrane (uredospores, Sordaria) or in the external membrane (teleutospores in Rust-Fungi), through which the germination takes place. Generally this does not occur till the spores have been set free: in some Ascomycetes germination commences inside the ascus (Taphrina, Sclerotinia). The different ways in which the spores germinate may be classified into three groups.

I. THE ORDINARY GERMINATION occurs by the spore emitting a germ-tube, which immediately developes into a mycelium. In spores with a double wall it is only the inner membrane which forms the germ-tube. In swarmspores a single wall is formed after the withdrawal of the cilia, and this, by direct elongation, becomes the germ-tube. The protoplasm accumulated in the spore enters the hypha, which, in pure water, can only grow as long as the reserve nourishment lasts.

=2.= GERMINATION WITH PROMYCELIUM differs only by the circumstance that the hypha developed from the germ-tube has a very limited growth, and hence it does not immediately develope into a mycelium, but produces conidia (Rust-and Brand-Fungi). This promycelium must only be regarded as an advanced development of a conidiophore or basidium.

=3.= THE YEAST-FORMATION of conidia consists in the production of outgrowths, very much constricted at their bases, from one or more places. Each of the conidia formed in this manner may again germinate in the same way. When sufficient nourishment is present, a branched chain of such conidia is formed, and these are finally detached from one another. Yeast-like buddings from the conidia are produced in various Fungi, e.g. Ascoidea, Protomyces, Ustilagineæ, Ascomycetes, Tremellaceæ, etc. In the Ustilagineæ these conidia are an important element in the development. The budding conidia of Exobasidium forms a “mould” on the nutritive solution. The yeast-like conidia are not to be confounded with the “Mucor-yeast” (comp. Mucoraceæ). For Saccharomyces see Appendix to the Fungi, page 176.

In a compound spore (i.e. when a mass of spores are associated together) each spore germinates on its own account. There are sometimes, however, certain among them which do not germinate, but yield their contents to those which do.

The length of time for which conidia can retain their power of germination is shortest (being only a few weeks) in those having thin walls and containing a large supply of water (Peronosporaceæ, Uredinaceæ). In many spores a resting period is absolutely necessary before they are able to germinate (resting spores). It has been observed in some spores and conidia, that the faculty of germinating may be preserved for several years if the conditions necessary for germination remain absent (Ustilagineæ, Eurotium, Penicillium).

The optimum, minimum and maximum temperatures required for the germination of the spores has been decided in the case of a good many Fungi. A large portion of the most common Fungi have their optimum at 20°C., minimum at 1–2°C, maximum at 40°C. In the case of pathogenic Fungi the optimum is adapted to the temperature of the blood. Fungi living in manure, whose spores are often adapted to germinate in the alimentary canals of warm-blooded animals, have an optimum corresponding to the temperature of these animals, but with a little margin.

=Systematic Division.=--The lowest class of the Fungi is that of the PHYCOMYCETES, which have an unicellular mycelium, sexual and asexual reproduction, and have doubtless sprung from sporangia-bearing, lower Green Algæ. From the Phycomycetes (and certainly from the Zygomycetes) spring two well defined branches, each with numerous distinct species; to the one branch belong the HEMIASCI and the ASCOMYCETES, to the other the HEMIBASIDII and the BASIDIOMYCETES. Ascomycetes and Basidiomycetes may be united under the title of MYCOMYCETES or HIGHER FUNGI. The Hemiasci and the Hemibasidii constitute the class of MESOMYCETES. The Hemiasci are an intermediate form between Zygomycetes and Ascomycetes; the Hemibasidii a similar group between the Zygomycetes and Basidiomycetes. Mesomycetes and Mycomycetes have only asexual reproduction; sexual reproduction is wanting. Their mycelium is multicellular.

Up to the present time about 39,000 species have been described.

Review of the divisions of the Fungi:--

Class I.--=Phycomycetes (Algal-Fungi).=

Sub-Class 1. =Zygomycetes.= Sub-Class 2. =Oomycetes.= Family 1. ENTOMOPHTHORALES. Family 2. CHYTRIDIALES. Family 3. MYCOSIPHONALES.

Class II. =Mesomycetes.=

Sub-Class 1. =Hemiasci.= Sub-Class 2. =Hemibasidii (Brand-Fungi).=

Class III.--=Mycomycetes (Higher Fungi).=

Sub-Class 1. =Ascomycetes.= Series 1. =Exoasci.= Series 2. =Carpoasci.= Family 1. GYMNOASCALES. } Family 2. PERISPORIALES. } Angiocarpic Exoasci. Family 3. PYRENOMYCETES. } Family 4. HYSTERIALES. } Hemiangiocarpic Exoasci. Family 5. DISCOMYCETES.} Family 6. HELVELLALES. Gymnocarpic (?) Exoasci.

Additional: ASCOLICHENES. Lichen-forming Ascomycetes.

Sub-Class 2. =Basidiomycetes.= Series 1.--Protobasidiomycetes. Partly gymnocarpic, partly angiocarpic. Series 2. Autobasidiomycetes. Family 1. DACRYOMYCETES. Gymnocarpic. Family 2. HYMENOMYCETES. Partly gymnocarpic, partly hemiangiocarpic. Family 3. PHALLOIDEÆ. Hemiangiocarpic. Family 4. GASTEROMYCETES. Angiocarpic.

Additional: BASIDIOLICHENES. Lichen-forming Basidiomycetes.

Additional to the Fungi: FUNGI IMPERFECTI. Incompletely known (Saccharomyces, Oidium-forms, etc.).

Class 1. =Phycomycetes (Algal-Fungi).=[12]

This group resembles Vaucheria and the other Siphoneæ among the Algæ.

ORGANS OF NUTRITION. The mycelium is formed of a single cell, often thread-like and abundantly branched (Fig. 78). Vegetative propagation by chlamydospores and oidia. Asexual reproduction by endospores (sometimes swarmspores) and conidia. Sexual reproduction by conjugation of two hyphæ as in the Conjugatæ, or by fertilisation of an egg-cell in an oogonium. On this account the class of the Phycomycetes is divided into two sub-classes: ZYGOMYCETES and OOMYCETES.

Sub-Class I. =Zygomycetes.=

Sexual reproduction takes place by zygospores, which function as resting-spores, and arise in consequence of conjugation (Fig. 81); in the majority of species these are rarely found, and only under special conditions. The most common method of reproduction is by endospores, by acrogenous conidia, by chlamydospores, or by oidia. Swarmspores are wanting. Parasites and saprophytes (order 6 and 7). The zygospores are generally produced when the formation of sporangia has ceased; e.g. by the suppression of the sporangial-hyphæ (Mucor mucedo), or by the diminution of oxygen; Pilobolus crystallinus forms zygospores, when the sporangia are infected with saprophytic Piptocephalis or Pleotrachelus.

=A.= Asexual reproduction only by sporangia.

Order 1. =Mucoraceæ.= The spherical sporangia contain many spores. The zygospore is formed between two unicellular branches (gametes).

The unicellular mycelium (Fig. 78) of the Mucoraceæ branches abundantly, and lives, generally, as a saprophyte on all sorts of dead organic remains. Some of these Fungi are known to be capable of producing alcoholic fermentation, in common with the Saccharomyces. This applies especially to Chlamydomucor racemosus (Mucor racemosus), when grown in a saccharine solution, and deprived of oxygen; the mycelium, under such conditions, becomes divided by transverse walls into a large number of small cells. Many of these swell out into spherical or club-shaped cells, and when detached from one another become chlamydospores, which abstrict new cells of similar nature (Fig. 79). These chlamydospores were formerly erroneously termed “mucor-yeast,” but they must not be confounded with the yeast-conidia (page 94). They are shortened hyphæ, and are not conidia of definite size, shape, and point of budding. Oidia are also found in Chlamydomucor.

The Mucoraceæ, in addition to the chlamydospores and oidia, have a more normal and ordinary method of reproduction; viz., by spores which are formed without any sexual act. Mucor has round sporangia; from the mycelium one or more long branches, sometimes several centimetres in length, grow vertically into the air; the apex swells (Figs. 78, 80) into a sphere which soon becomes separated from its stalk by a transverse wall; in the interior of this sphere (sporangium) a number of spores are formed which eventually are set free by the rupture of the wall. The transverse wall protrudes into the sporangium and forms the well-known columella (Fig. 80 d, e). The formation of spores takes place in various ways among the different genera.

SEXUAL REPRODUCTION by conjugation takes place in the following manner. The ends of two hyphæ meet (Fig. 81) and become more or less club-shaped; the ends of each of these are cut off by a cell-wall, and two new small cells (Fig. 81 A) are thus formed, these coalesce and give rise to a new cell which becomes the very thick-walled zygote (zygospore), and germinates after period of rest, producing a new hypha, which bears a sporangium (Fig. 81 E).

Mucor mucedo, Pin-mould, resembles somewhat in appearance Penicillium crustaceum and is found growing upon various organic materials (bread, jam, dung, etc.).

Pilobolus (Figs. 83, 84) grows on manure. Its sporangium (Fig. 84 a″) is formed during the night and by a peculiar mechanism (page 92) is shot away from the plant in the course of the day. This generally takes place in the summer, between eight and ten a.m. The sporangium is shot away to a height which may be 300 times greater than that of the plant itself, and by its stickiness it becomes attached to portions of plants, etc., which are in the vicinity. If these are eaten by animals, the spores pass into the alimentary canal and are later on, sometimes even in a germinating condition, passed out with the excrement, in which they form new mycelia.

Phycomyces nitens (“Oil-mould”) is the largest of the Mould Fungi; its sporangiophores may attain the height of 10–30 c.m.

Order 2. =Rhizopaceæ.= Rhizopus nigricans (Mucor stolonifer) which lives on decaying fruits containing sugar, on bread, etc., has, at the base of the sporangiophores, tufts of rhizoids, i.e. hyphæ, which function as organs of attachment. From these, “runners” are produced which in a similar manner develope sporangiophores and rhizoids.

Order 3. =Thamnidiaceæ.= On the same sporangiophore, in addition to a large, terminal, many-spored sporangium, many smaller, lateral sporangia are formed with a few spores. Thamnidium.

=B.= Asexual reproduction by sporangia and conidia.

Order 4. =Choanephoraceæ.= Choanephora with creeping endophytic mycelium, and perpendicular sporangiophores.

Order 5. =Mortierellaceæ.= Mortierella polycephala produces on the same mycelium conidia and sporangiophores. M. rostafinskii has a long stalked sporangiophore, which is surrounded at its base by a covering of numerous felted hyphæ.

=C.= Asexual reproduction only by conidia.

Order 6. =Chætocladiaceæ.= The conidia are abstricted singly and acrogenously. Chætocladium is a parasite on the larger Mucoraceæ.

Order 7. =Piptocephalidaceæ.= The conidia are formed acrogenously and in a series, by transverse divisions. The zygospore arises at the summit of the conjugating hyphæ, which are curved so as to resemble a pair of tongs. Piptocephalis and Syncephalis live parasitically on the larger Mucoraceæ.

Sub-Class 2. =Oomycetes.=

Sexual reproduction is oogamous with the formation of brown, thick-walled oospores which germinate after a period of rest. Asexual reproduction by conidia and swarmspores. Parasites, seldom saprophytes.

The oospores are large spores which are formed from the egg-cell (oosphere) of the oogonium (oosporangium, Fig. 89, 95). A branch of the mycelium attaches itself to the oogonium and forms at its apex the so-called “antheridium” (pollinodium[13]): this sends one or more slender prolongations (fertilising tubes) through the wall of the oogonium to the egg-cell.

A fertilisation, a passage of the contents of the antheridium to the egg-cell, has as yet only been observed in Pythium; in Phytophthora only one small mass of protoplasm passes through the fertilising tube to the egg-cell; in Peronospora and the Saprolegniaceæ no protoplasm can be observed to pass through the fertilising tube, so that in these instances parthenogenesis takes place; Saprolegnia thuretii, etc., have generally even no antheridia, but nevertheless form normal oospores. Fertilisation of the egg-cell by means of self-motile spermatozoids is only found in Monoblepharis sphærica.

=A.= Asexual reproduction by conidia only.

Family 1. =Entomophthorales.=

The mycelium is richly branched. The family is a transitional step to the conidia-bearing Zygomycetes, since the oospores of many members of this family arise, and are formed, like zygospores.

Order 1. =Entomophthoraceæ.= Mycelium abundantly developed. This most frequently lives parasitically in living insects, causing their death. The conidiophores forming the conidial-layer project from the skin, and abstrict a proportionately large conidium which is ejected with considerable force, and by this means transferred to other insects. These become infected by the entrance of the germ-tube into their bodies. The spherical, brown resting-spores develope inside the bodies of insects and germinate by emitting a germ-tube.

GENERA: Empusa has a good many species which are parasitic on flies, moths, grasshoppers, plant-lice. The conidia emit a germ-tube which pierces the skin of the insect; a number of secondary conidia are then produced inside its body, by division or by gemmation similar to that taking place in yeast, each of which grows and becomes a long unbranched hypha, and these eventually fill up the body of the animal, causing distension and death. Each of these hyphæ projects through the skin, and abstricts a conidium, which is ejected by a squirting contrivance. The best known species is E. muscæ (Fig. 85), which makes its appearance epidemically towards autumn on the common house-fly, and shows itself by the dead flies which are found on the windows and walls attached by their probosces, distended wings, and legs. They have swollen abdomen, broad white belts of hyphæ between the abdominal rings, and are surrounded by a circle of whitish dust formed by the ejected conidia.--Entomophthora sends out, at definite places, from the mycelium hidden in the insect’s body, bundles of hyphæ, which serve the purpose of holding fast the dead insects, the ramifications attaching themselves to the substratum: the conidiophores are branched, the conidia are ejected by the divisional walls between the hyphæ and the conidia dividing into two layers, those which terminate the hyphæ suddenly expanding and throwing the conidia into the air. E. radicans makes its appearance epidemically on caterpillars.

=B.= Asexual reproduction by zoospores or conidia.

Family 2. =Chytridiales.=

In this family the mycelium is very sparsely developed or is wanting. The entire plant consists principally or entirely of a single zoosporangium whose zoospores have generally one cilium. The resting-spores arise either directly from the zoosporangium, which, instead of forming zoospores, surrounds itself by a thick cell-wall; or they are formed by the conjugation of two cells (in which case they are spoken of as oospores). Microscopic Fungi, parasitic on water plants (especially Algæ) or small aquatic animals, seldom on land plants.

Order 1. =Olpidiaceæ.= Without mycelium. Swarmspores and resting-spores.

In the Olpidieæ, the swarmspores, probably, most frequently form themselves into a plasmodium (naked mass of protoplasm) which may become a single zoosporangium or a resting sporangium. Olpidium trifolii occurs in Trifolium repens.--In the Synchytrieæ the plasmodium emerging from the swarmspores breaks up either at once, or after a period of rest, into smaller plasmodia, each of which will become a zoosporangium. Synchytrium anemones is found on Anemone nemorosa; S. mercurialis on Mercurialis perennis; S. aureum on many plants, particularly Lysimachia nummularia.

Order 2. =Rhizidiaceæ.= Mycelium present. Zoospores and resting-spores.

Chytridium (Fig. 86). Obelidium (Fig. 87) is bicellular; the one cell is the mycelium, the other the zoosporangium; found on insects. The species of Cladochytrium are intercellular parasites on marsh plants. Physoderma.

Order 3. =Zygochytriaceæ.= Mycelium present. Zoospores and oospores. The latter are the product of the conjugation of two cells (Fig. 88).

Polyphagus euglenæ on Euglena viridis. Urophlyctis pulposa on species of Chenopodium.

Family 3. =Mycosiphonales.=

The mycelium is bladder-like or branched. Zoospores. Sexual reproduction by oospores, which are produced in oogonia. The latter are fertilised, in some forms, by the antheridium.

Order 1. =Ancylistaceæ.= The entire bladder-like mycelium is used for the construction of zoosporangia, oogonia, or antheridia. Lagenedium is parasitic on Spirogyra, etc.

Order 2. =Peronosporaceæ.= Almost entirely parasites. The unicellular, often very long and abundantly branched mycelium lives in the intercellular spaces of living plants, especially in the green portions, and these are more or less destroyed and deformed in consequence. Special small branches (suction-organs, “haustoria”) are pushed into the cells in order to abstract nourishment from them. Both oospores and conidia germinate either immediately, or they develope into sporangia with swarmspores, having always two cilia. Only one oospore is formed in each oogonium; its contents (Fig. 89) divide into a centrally placed egg-cell and the “periplasm” surrounding it; this is of a paler colour and on the maturity of the oospore forms its thick, brown, external covering.

The Potato-fungus (Phytophthora infestans) is of great interest. Its thallus winters in the Potato-tuber; other organs for passing the winter, such as oospores, are not known. When the tuber germinates, the Fungus-hyphæ penetrate the young shoot and keep pace with the aerial growth and development of the plant. The conidiophores emerge through the stomata, especially on the under side of the leaves; they branch like a tree (Fig. 90), and appear to the naked eye as a fine mould on the surface of the plant. The disease soon makes itself known by the brown colouring of those parts of the plant which are attacked, and by their withering. An ovoid conidium arises at first by the formation of a dividing wall at the apex of each branch of the conidiophore (Fig. 90 c c), and immediately underneath it another is formed, which pushes the first to one side, and so on. These conidia sometimes germinate directly, and form a mycelium, but most frequently their protoplasm divides into many small masses, each of which becomes a pear-shaped zoospore provided with two cilia (Fig. 91). Water is required for their germination, and when the ripe conidia are placed in a drop of water the swarm-cells are formed in the course of about five hours. They swarm about in rain and dewdrops in the Potato-fields, and are carried with the water to the Potato-plants and to the tubers in the soil. The wind also very easily conveys the conidia to healthy Potato-fields and infects them. The enormous quantity of conidia and swarm-cells that may be formed in the course of a summer explains the rapid spreading of the disease; and the preceding makes it clear why wet summers are favourable to its existence. When the swarm-cells germinate, they round off, and then surround themselves with a cell-wall which grows out into the germ-tube, and pierces through the epidermis of the host-plant (Fig. 92). Having entered the host, a new mycelium is formed. The potato disease, since 1845, has been rampant in Europe; it has, no doubt, been introduced from America, which, it must be remembered, is the home of the Potato-plant.

The conidia exhibit various characters which are employed for the separation of the genera. Pythium is the most simple form. The contents of the terminally-formed conidia emerge as a spherical mass and divide into swarmspores. P. de Baryanum lives in the seedlings of many different Flowering-plants, which it completely destroys.--Phytophthora is distinguished by the circumstance that the sparsely-branched conidiophores bear, sympodially, chains of conidia. Besides the Potato-fungus (see above), Ph. fagi belongs to this group; it developes oospores very abundantly, and does great harm to seedlings of the Beech, Sycamore, and Pine trees.--Peronospora generally has conidiophores which are repeatedly forked, and bear a conidium on each of the most extreme ramifications. Many do great harm to their host-plants. P. viticola, on Vines, and P. nivea, on umbelliferous plants, have swarmspores, which are absent in the following species of this genus: P. sparsa, on Roses; P. gangliformis, on composites; P. alsinearum, on Stitchwort; P. parasitica, on cruciferous plants; P. viciæ, on Vetches and Peas; P. schachtii, on Beets; P. violacea, on the flowers of Scabiosa; P. radii, on the ray-florets of Matricaria.--Cystopus (Albugo) has the conidia developed in chains, which form a cohesive white layer underneath the epidermis of the host-plant. Cystopus candidus, on cruciferous plants, especially Shepherd’s Purse and Brassica; the germination commences on the cotyledons, and from this point the mycelium developes together with the host-plant; C. cubicus, on the leaves of Compositæ.

Order 3. =Saprolegniaceæ=, Water-Fungi which live as saprophytes on organic remains lying in water, for instance, on dead flies (Fig. 93), worms, remains of plants; but they may also make their appearance on living animals, being frequently found, for example, on the young trout in rearing establishments.

The thallus is a single, long and branched cell. It has one portion which serves as root, and lives in the substratum, where it ramifies abundantly for the purpose of absorbing nourishment; and another portion projecting freely in the water, and sending out hyphæ on all sides (Fig. 93). The asexual reproduction takes place by swarmspores (Fig. 94), which are developed in large sporangia; these swarmspores generally possess two cilia, and on germination grow into new plants. The entire protoplasm in the oogonium is formed into one or more oospheres, without any surrounding “periplasm.” The oospheres may not be fertilised (p. 100), and then develope parthenogenetically.

Genera: Saprolegnia, whose swarmspores disperse immediately after having left the sporangium. S. ferax is the cause of a disease in fish (“Salmon disease”) and in the crayfish.--Achlya, whose swarmspores accumulate in a hollow ball before the mouth of the sporangium.--Leptomitus has strongly indented hyphæ, causing a “linked” appearance. L. lacteus is frequent in the waste matter from sugar factories.--Monoblepharis deviates from the others by the greater development of its fertilising process; the oosphere, situated in an open oogonium, becoming fertilised by self-motile spermatozoids, which are provided with a cilium at the posterior end.

Class 2. =Mesomycetes.=

The Mesomycetes are intermediate forms between the Phycomycetes and the Higher Fungi. In the vegetative organs, and in the multicellular hyphæ, they resemble the Higher Fungi; the methods of reproduction, however, show the characters of the Phycomycetes, namely sporangia and conidiophores of varying size and with varying number of spores; definite and typically formed asci and basidia are not present. Sexual reproduction is wanting. The HEMIASCI are transitional between the Phycomycetes and the Ascomycetes, the HEMIBASIDII (Brand-Fungi) form the transition to the Basidiomycetes.

Sub-Class 1. =Hemiasci.=

The Hemiasci are Fungi with sporangia which, although resembling asci, yet have not, however, a definite form and a definite number of spores. Besides endospores, conidia, chlamydospores and oidia are found.

Order 1. =Ascoideaceæ.= Ascoidea rubescens forms irregular, reddish-brown masses in the sap issuing from felled Beeches. It has free sporangia, which resemble asci in their structure, in the development and ejection, and in the definite shape and size of the spores. The formation of the sporangia takes place when the nutriment is nearly exhausted, and resembles that of the conidia, since they are developed from the end of a hypha which enlarges, and the swelling becomes separated by a transverse wall. Within the sporangia numerous spores of a cap-like form are developed, which are set free through an opening at the apex. Sporangia are formed successively at the apex of the same hypha, the second commencing to develope as the first is dehiscing. Conidia and sporangia are not formed simultaneously; the former may be considered as closed sporangia.

Order 2. =Protomycetaceæ.= Protomyces pachydermus causes hard swellings on the stems and leaf-stalks of the Cichorieæ (Taraxacum, etc.). These swellings consist of chlamydospores (resting-spores), which germinate and become free, ascus-like sporangia, with numerous small spores. In nutritive solutions the chlamydospores form conidia with yeast-like buddings. P. macrosporus on Ægopodium, and other Umbelliferæ.

Order 3. =Thelebolaceæ.= Thelebolus stercoreus, is found on the dung of deer, hares, and rabbits, and has closed sporangia, which resemble asci in their shape and regular construction, and in the ejection of spores. The covering encloses only one sporangium, even where the sporangia arise close together.

This order, by reason of the covering of the sporangia, forms the transition from the Hemiasci to the Carpoasci, while the two first supply an intermediate step to the Exoasci.

Sub-Class 2. =Hemibasidii, Brand-Fungi.=

The Brand-Fungi (also known as USTILAGINEÆ) are Fungi with basidia-like conidiophores, which, however, have not yet advanced to a definite form or number of conidia. They are true parasites, whose mycelium spreads itself in the intercellular spaces of Flowering plants. The mycelium is colourless, quickly perishable, has transverse walls at some distance from each other (Fig. 96), and sends out haustoria into the cells of the host-plant.

It most frequently happens that the germ-tube enters the host-plant at its most tender age, that is, during the germination of the seed; the mycelium then wanders about in the tissues of the shoot during its growth, until it reaches that part of the plant where the spores are to be formed. The spore-formation takes place in the same way in all those species whose brand-spores are developed in the floral parts of the host-plant. Many Brand-Fungi have, however, a more local occurrence, and the mycelium is restricted to a smaller area of the leaf or stem. Those organs of the host-plant in which the brand-spores are developed often become strongly hypertrophied. In perennial plants the mycelium winters very often in the rhizome.

The brand-spores are the winter resting-spores of the Brand-Fungi. They arise in the tissues of the host-plant, which is often destroyed, and become free through the rupture of the epidermis; they are thick-walled, generally brown or violet, and very often possess warts, spines, or reticulate markings. Fruit-bodies, that is enclosed organs of reproduction, are found in few genera (Sphacelotheca, Graphiola; Doassansia, Fig. 97). In Tolyposporium, Tuburcinia, Thecaphora (Fig. 102), etc., the brand-spores are united into a ball of spores. On germination the brand-spores behave as chlamydospores, namely, as the fundament of conidiophores, by emitting a short germ-tube, i.e. a conidiophore (“promycelium”). The USTILAGINACEÆ (Fig. 99, 2) have a short transversely divided conidiophore, with laterally developed conidia (comp. the basidia of the Protobasidiomycetes). The conidiophores of the TILLETIACEÆ are undivided (unicellular promycelia), and bear the conidia terminally, and so resemble the basidia of the Autobasidiomycetes.

In Tilletia, Entyloma, Neovossia, Tuburcinia, the brand-spores germinate and form basidia-like conidiophores with spindle-shaped conidia; their mycelium, on the other hand, produces later only single, sickle-shaped conidia, so that two kinds of conidia are found, as in a few Basidiomycetes. In some species, e.g. Ustilago hordei, the brand-spores only germinate vegetatively and form a mycelium. In nutritive solutions (solutions of dung, etc.) where they live as saprophytes, the brand-spores of many species emit germ-tubes, and on these, yeast-like conidia are produced by repeated budding, which grow into mycelia only when the nutritive solution is exhausted. These conidia have not the power of producing alcoholic fermentation. The very numerous conidia, which are found in the dung of herbivorous animals, are probably the yeast-conidia of Brand-Fungi. The brand-spores, which are eaten by animals with the grain and hay, pass into the dung and without doubt give rise to a very rich multiplication of yeast-conidia.

The conidia (also called “sporidia”) of many species unite generally into an H-form (Figs. 97, 4; 100 h; 101, 4). This union in pairs does not, however, take place with a view to germination, there is no fusion of nuclei, and therefore in this “fusion” there is no sexual act.

Order 1. =Ustilaginaceæ.= Conidiophores with transverse walls and lateral conidia.--Ustilago (Fig. 99) generally developes its spores in the floral organs of its host-plant, the ovary or anthers, where they arise from hyphæ, and form a slimy mass which when mature becomes a black dust.

To this order belong U. avenæ, parasitic on Oats, U. hordei and U. nuda (U. jenseni), on Barley; these are the usual cause of “Smut” on cereals. U. hypodytes on straw of Elymus and Agropyrum. U. filiformis in the leaves of Glyceria. U. caricis transforms the fruits of various species of Carex into black, dusty balls. U. violacea developes its violet spore-powder in the anthers of the Caryophyllaceæ. U. tragopogonis, transforms entire inflorescences of Tragopogon into a black-violet mass. Among the largest are U. grandis, which causes the large swollen nodes in the stem of Phragmites, and the Maize Blight, U. maydis, which produces outgrowths about the size of a hand on the spadix of the Maize.

Order 2. =Tilletiaceæ.= Conidiophores undivided, generally several conidia arise at their apices.--Tilletia tritici, the Stinkbrand on Wheat (Fig. 100). The mycelium lives in Wheat-plants, producing its spores in the ovary after the whole interior of this body has been destroyed by the mycelium, with the exception of the external layer of the wall of the ovary, which remains essentially unaltered and encloses the closely packed, firm mass of spores (Fig. 100 d). The grains of Wheat thus attacked are shorter and thicker than the sound ones, and the ears show the presence of this Fungus by their erect position, and the wide separation of the chaff (Fig. 100 a). The unpleasant odour of the ovary prior to the ripening of the spores, has given the name “Stinkbrand,” and, in like manner, its hardness when it encloses the ripe spores, is the reason of its being also called “Stonebrand.” On account of this hardness, the diseased grains are readily harvested together with the healthy ones, which become infected by the spores at the threshing. T. lævis (T. fœtens) also occurs on Wheat and has smooth brand-spores.

Entyloma (Fig. 96), a genus with numerous species, which appear in spots on the leaves of the host-plant, and Tuburcinia (Fig. 98), which makes its appearance on the Primulaceæ, produce white conidia-spots on the surface of the host-plant. The first-named has single spores, the latter has its spores closely massed together.--Urocystis (Fig. 101) has its spores surrounded by a number of small and lighter coloured barren spores. U. occulta, Rye-stem Blight, forms its spores in long streaks in the stems and leaves of the Rye, and does considerable damage. U. cepulæ on Onions. U. violæ forms large dark-violet swellings in the leaf-stalk and stems of Violets.--Thecaphora (Fig. 102) appears in seedlings of Convolvulus and Astragalus.

As a means of protection against the Smut-Fungi which make their appearance on the different cereals, a submersion of the grains in a solution of blue vitriol (½%) for twelve hours, or better still, submerging for five minutes in water heated to 53–55° C (Jensen’s method) is employed.

Class 3. =Mycomycetes, Higher Fungi.=

The MYCOMYCETES are not entirely aquatic in habit; they have hyphæ with transverse walls, but no sexual reproductive organs. The asexual reproduction takes place in very different ways; by endospores (in asci), conidia, basidiospores, chlamydospores, and oidia. Swarmspores are never found.

Two chief methods of reproduction may be distinguished, and hence the class may be divided into two large sub-classes:--the ASCOMYCETES (with asci), and the BASIDIOMYCETES (with basidia).

Sub-Class 1. =Ascomycetes.=

The main characteristic which distinguishes the Ascomycetes is the ascus; a name given to a sporangium of a definite shape and size, and containing a definite number of spores. The shape is generally club-like or spherical, the number of spores 8 (in some 2, 4, 16 or more), see Figs. 103, 105, 108, 110, 113, 116, 120, 121, 123, 129.

In the lowest forms, the EXOASCI, the ascus springs directly from the mycelium without the formation of a fruit-body (i.e. ascocarp). In the higher forms, which contain many species, the CARPOASCI, the asci are united and form ascocarps which may be more or less enclosed (angiocarpic, hemiangiocarpic, and probably gymnocarpic).

The hyphæ of the Mycelium in some remain free, in others they are felted together and form thick strands or flat, cushion-like bodies (compare in particular the stromata of the Pyrenomycetes). Some species form sclerotia (Figs. 116, 128).

Asexual reproduction by means of conidia is known in many species as the principal means of reproduction, and the one which affords the most rapid means of distribution. The conidia may be produced on conidiophores (Fig. 109), in conidial-layers (Fig. 122), and often in conidiocarps (pycnidia, Figs. 120 d, e; 123 a; 124 b.). These last occur partly as the so-called “spermogonia” (that is, pycnidia with microconidia). The conidiophores never approach the basidia.

In many species the ascospores germinate and form conidia immediately (Nectria cinnabarina, Sclerotinia, Taphrina, etc.), sometimes while they are still in the ascus and before their ejection (Taphrina, Fig. 105 a). In many instances the conidia by means of continued budding can, for a longer or shorter time, produce yeast-conidia, e.g. Taphrina. In many other cases the conidia arise from the germ-tubes of the ascospores, or at any part of the mycelium. The unripe asci of Taphrina, when placed in water, develop conidia at their apices. The Sclerotinia-species produce numerous conidia whose germination has never been observed. The formation of conidia and asci sometimes takes place on the same fruit-body. In Heterosphæria patella the conidia and asci are developed successively in the same fruit-body; in the ascocarps of Dermatea frangula and Sclerotinia sclerotiorum the formation of conidia may take place. The ascocarps frequently arise from the conidial-layers (Nectria cinnabarina, etc.). This relationship of the two forms of reproduction to each other may be explained by considering that both have descended phylogenetically from sporangia.

Sometimes chlamydospores and oidia also appear in the Ascomycetes; on germination, however, they do not, as in Protomyces, form sporangia, and on this account cannot be distinctly distinguished from conidia.

The asci are morphologically the highest form of reproduction and are always found at the close of the development of these Fungi; the accessory forms of reproduction are first developed, but a well-defined alternation of generations does not occur.

In the Ascomycetes there are more than 11,000 described species, which can be classed as follows:--

Series 1. EXOASCI. Only one order. „ 2. CARPOASCI. Family 1. Gymnoascales, } „ 2. Perisporiales, } Angiocarpic Carpoasci. „ 3. Pyrenomycetes, } „ 4. Hysteriales, } Hemiangiocarpic Carpoasci. „ 5. Discomycetes,} „ 6. Helvellales, Gymnocarpic (?) Carpoasci. Additional Ascolichenes: Lichen-forming Ascomycetes.

Series 1. =Exoasci.=

Ascomycetes with FREE ASCI; sometimes also conidia, chlamydospores and oidia. One order.

Order. =Taphrinaceæ.= Of the genera belonging to this order, Taphrina, Endomyces, and Ascocorticium, the first is most important.

Endomyces decipiens is a parasite in the fruit-body of Armillaria mellea; E. magnusii lives in the gelatinous, fermenting exudations of Oak-trees; Ascocorticium albidum is found under the bark of the Fir-tree. Endomyces has chlamydospores and oidia.

The species of Taphrina are parasites, whose free asci may be found in great numbers, generally closely pressed together, on the parts of plants which they have attacked. The asci are developed directly from the ascogenous cells of a fertile, generally sub-cuticular, hypha, which arises from the sterile mycelium. The latter arises from the germinating ascospore, and may hibernate in the tissues of its host, particularly in the winter buds, and then with the commencement of the next period of vegetation it continues its growth side by side with that of its host. The hyphæ ramify in the intercellular spaces or beneath the cuticle, but have no haustoria. The ascospores (Fig. 105 A) and unripe asci may produce conidia.

Very remarkable appearances, and swellings of the attacked tissues, are produced when the mycelium is perennial; for example, the “Witches’-brooms” and “Pockets.” The hard, hollow, stoneless plums, known as “Pocket” or “Bladder” Plums, are produced by considerable changes in the tissues of the fruit; these are caused particularly by T. pruni on several species of Prunus. The “Witches’-brooms,” on the contrary, are deformations of entire twigs or branches, and often attain a very large size. They occur on Alnus incana, caused by T. epiphylla; on Carpinus betulus, by T. carpini; on Cherry-trees, by T. cerasi; on Plum-trees, by T. insititiæ; on Birches, by T. turgida and T. betulina. T. deformans attacks the leaves of the Peach, and causes them to curl.

When a perennial mycelium is wanting, the infection is confined as a rule to white or yellow spots on the leaves, e.g. the commonest, T. sadebeckii, on Alnus glutinosa, and T. aurea on species of Populus. T. alni incanæ (Fig. 106) causes considerable hypertrophies on the pistillate catkins of the Alder, which may be compared to the “pockets” of Prunus.

Series 2. =Carpoasci.=

The Carpoasci are Ascomycetes, whose asci are enclosed in fruit-bodies, i.e. ascocarps. The accessory means of reproduction are free conidiophores (Fig. 109), conidial-layers (Fig. 122), conidiocarps (Fig. 120 D, E, etc.), chlamydospores and oidia.

For the different methods of distributing the ascospores, see p. 92.

Of the six families of the Carpoasci, the first three--Gymnoascales, Perisporiales, and Pyrenomycetes--are ANGIOCARPIC (that is, the ascocarp remains closed throughout its existence, and does not dehisce when ripe); the fourth and fifth families (Hysteriales and Discomycetes), on the other hand, are HEMIANGIOCARPIC (the ascocarp, here also called an apothecium, is closed in the early stages, but opens at the commencement of ripening and exposes a hymenium of crowded asci); the family of Helvellales has probably GYMNOCARPIC (or hemiangiocarpic) fruit-bodies.

Family 1. =Gymnoascales.=

The ascocarps are surrounded by a spongy and incomplete envelope. One order, poor in species.

Order =Gymnoascaceæ=.--The ascocarps are borne sometimes solitarily, or sometimes coiled together. Gymnoascus reessii forms small bodies about 1 mm. in diameter on old horse-dung, which at first are white and afterwards orange-red.--Ctenomyces serratus lives on the old feathers in birds’ nests.

Family 2. =Perisporiales.=

The ascocarps are surrounded by a complete envelope without any opening: the fruit-bodies are cleistocarpic; the spores are only liberated after the disintegration of the fruit-bodies. Paraphyses are wanting. The two first orders have in addition the means of reproduction by conidia.

Order 1. =Erysiphaceæ, Mildews.= The Fungi belonging to this order are epiphytic parasites, whose mycelium, somewhat resembling a cobweb, may be seen on the leaves and other green portions of plants (see Figs. 107, 108). The hyphæ ramify in all directions upon the surface of their host, and emit haustoria which penetrate the epidermal cells, and thus derive the necessary nutriment. The Mildew-Fungi thus belong to the obligate parasites, and during their growth dwarf and destroy the portions of their host on which they live. The reproduction takes place in the first instance by abstriction of conidio-chains from the end of special branches (Fig. 108 c, a hypha is seen in the act of detaching a conidium). The conidia may germinate immediately, and thus quickly reproduce their species. When present in large numbers they appear as a white meal covering the surface of the plant on which the fungus is found. Later on appear the dark brown, spheroid ascocarps (Fig. 108 a) which, although small, are generally just visible to the naked eye as black specks.

A characteristic feature of the Mildew-Fungi is the thin, pseudo-parenchymatous covering of the ascocarp, enclosing one (Podosphæra and Sphærotheca; compare Thelebolus among the Hemiasci) or a few asci (Fig. 108 c), which do not form any hymenium, but are irregularly placed. The cells of the ascocarp-envelope are often prolonged into hair-like appendages. The ascocarps are developed from the mycelium at places where two hyphæ cross each other (Fig. 107). At these places two short and erect hyphæ are produced side by side. The one from the lower hypha (Fig. 107 c) assumes an ellipsoidal shape, and is known as the archicarp or ascogone, while the other (“pollinodium”) arches over the ascogone. From the latter one ascus may be at once developed (Sphærotheca, etc.), or after its division several asci may be produced, each developed from one division. The sterile hypha (termed “pollinodium,” since it was formerly, but erroneously, supposed to fertilise the ascogone) produces a number of branches, and forms the pseudo-parenchymatous envelope of one cell in thickness, enclosing the asci.

Many plants, both cultivated and wild, are attacked by various species of Mildew. A common means of prevention against their attacks is to dust the diseased parts with sulphur.

Sphærotheca pannosa occurs on the leaves of Roses, and on the fruit of Peaches and Apricots. S. castagnei on Humulus, Cucumis, etc.--Erysiphe tuckeri grows on the leaves and fruit of the Vine; it spins its hyphæ over the bunches of grapes, curtails their growth, and causes them to burst, and to become decayed and rotten (Grape-disease). The Fungus was first noticed in England in 1845, and later was found in all countries where grapes are grown. It is only known in the conidial form (“Oidium tuckeri”). Many other species of Erysiphe are found on herbaceous plants.--Microsphæra has appendages which are repeatedly forked at their extremities. M. grossulariæ on Ribes grossularia.--Uncinula has appendages with spirally-coiled extremities; on Salix and Acer.--Phyllactinia has a circle of bristle-like appendages with dilated bases. P. guttata on Corylus, Fraxinus, Fagus, etc.

Order 2. =Perisporiaceæ=, Moulds and Mildews. A group of Fungi widely distributed and found in all situations. Usually they have a well-developed surface mycelium, and small, round, seldom conspicuous ascocarps, containing ovoid, pulley-like spores. They are partly saprophytic, partly parasitic, in the latter condition having a brown mycelium.

Eurotium glaucum (= E. herbariorum, Figs. 109, 110) and E. repens live on dead organic matter, preserved fruits, etc. The conidial forms of both species are known as “Moulds” (Fig. 109), and formerly were described under the name “Aspergillus glaucus.” The conidia for some time remain attached to each other in chains (Fig. 109 a); they are abstricted from sterigmata arranged radially on the spherical, swollen end of the conidiophore. The small yellow or brownish ascocarps are frequently found in herbaria, especially when the specimens have been insufficiently dried. Aspergillus fumigatus and others are pathogenic, causing mycosis in warm-blooded animals.

Penicillium crustaceum (P. glaucum, Figs. 111, 112) is an exceedingly common “Mould.” Its mycelium appears very frequently on any organic matter which is permitted to remain untouched, and soon covers it with a dense mass of blue-green conidiophores. These branch at their summits and bear flask-shaped cells from which the conidia are abstricted. The ascocarps which, both in size and colour, resemble grains of sand, have only been obtained in luxuriant cultivation with a limited supply of oxygen.

Capnodium salicinum (Fumago salicina, Cladosporium fumago), a common Mildew, forms dark overgrowths on the leaves and branches of various shrubs (Poplars, Elms, Willows) and on Hops. The conidia appear in various forms, as on conidiophores, in conidiocarps with large multicellular conidia, and in conidiocarps with small unicellular conidia; in nutritive solutions yeast-like conidia are also developed.--Apiosporium pinophilum produces mildew on the leaves of Abies alba and Picea excelsa. (The conidial-forms were formerly described as “Antennaria pinophila”).

Order 3. =Tuberaceæ, Truffles.= The Fungi belonging to this order are entirely subterranean. The mycelium is filamentous, and partly parasitic upon the roots of plants, especially trees, in its neighbourhood; it is then known as Mycorhiza. The fruit-body is relatively large, in some cases about the size of a hen’s egg. Internally it is traversed by a number of winding passages (Fig. 113 a), the walls of which are coated with the asci. The asci (b) contain only a small number of spores, and these are set free by the putrefaction of the fruit-body. Conidia are unknown.

Tuber melanosporum, T. brumale, T. æstivum, and other species are edible. Terfezia leonis and Choiromyces mæandriformis are also edible. The Truffles are always found in woods and under trees, and disappear when these are destroyed. France and Italy produce the best and the largest number of Truffles, which are hunted by specially trained dogs and pigs.

In Elaphomyces (Stag-Truffle) the fruit-body has a corky external layer, and is inedible. Some of the species are found in this country. E. granulatus is parasitic on the roots of the Fir.

Family 3. =Pyrenomycetes.=

In this family the hymenium is enclosed in small fruit-bodies, perithecia (Fig. 120 b), which appear to the naked eye as small dots. In shape they resemble a globe or a flask with a narrow mouth, through which the spores are ejected (peronocarpic ascocarps). Different kinds of reproduction--conidia, pycnidia (chiefly with microconidia), chlamydospores, and perithecia--are found in the same species. The various stages in the life-history of these Fungi are so dissimilar, that formally they were considered to be different genera. Ergot furnishes a very good example.

This family may be subdivided into 3 sub-families.

Sub-Family 1. =Hypocreales.=

The perithecia are pale, fleshy, brightly coloured, and generally aggregated on a stroma. Conidia and chlamydospores occur very frequently. Only one order.

Order. =Hypocreaceæ.= In this order the majority are parasites upon Flowering-plants (Nectria, Polystigma, Epichloë, Claviceps); but some are parasites upon Fungi (Hypomyces, Melanospora), or upon insects (Cordyceps).

The most important member of this order is the ERGOT (Claviceps purpurea, Figs. 114, 115, 116). This Fungus is found in the flowers of many species of Grasses, especially the Rye, attacking and destroying the ovaries. In the FIRST or CONIDIAL STAGE of the attack, the ovaries are found covered with a white, irregularly folded mycelium (Fig. 114 m, Fig. 115), formed of numerous hyphæ woven together and penetrating the wall of the ovary. From these a number of hyphæ (Fig. 114 a) project into the air and abstrict from their apices the conidia (b) which serve as reproductive organs. The mycelium also secretes a sticky, stinking fluid (honey-dew) in which the conidia are embedded in great numbers. The honey-dew exudes from the bases of the glumes, and is greedily sought by flies, which thus carry the conidia to other ovaries. In this manner fresh ears are infected, which might escape were the conidia only distributed by the wind. This stage formerly was regarded as an independent Fungus, known as Sphacelia segetum (Fig. 115). On germination, the conidia produce either a new mycelium (Fig. 114 d, c), or new conidia. The SECOND or SCLEROTIUM STAGE is the one in which the Fungus passes the winter. The mycelium penetrates deeper and deeper into the attacked ovaries, their tissues are destroyed and replaced by the hyphæ, which gradually become more and more felted together. A firm, pseudo-parenchymatous mass of hyphæ is thus formed at the base of the loosely-woven Sphacelia, which is in part transformed into the hard sclerotium, and the remainder thrown off. A dark, hard, poisonous body, longer than the natural grain, is thus formed; these bodies are known as Ergots, and were formerly considered to be a distinct species,--Sclerotium clavus (“Secale cornutum,” Ergot, Fig. 116 A, c). The THIRD STAGE, described as Claviceps purpurea, is developed in the following spring from the germinating sclerotium, which produces dark-red stromata with short stalks. In the stroma numerous perithecia with asci and ascospores are produced. The latter may infect young flowers of the cereals, in which the disease is then developed as before.

Several species of the genus Nectria, with blood-red perithecia, are found as dangerous parasites, especially N. ditissima, which causes “Canker” in the Beech, Ash, and Apple, etc.; N. cucurbitula, which appears on Pine-trees, and N. cinnabarina (Fig. 117), whose conidial form was formerly named Tubercularia vulgaris.--Polystigma rubrum forms shining red spots on the green leaves of Prunus-species.--Epichloë typhina is parasitic on the sheaths of Grasses, on which it first forms a white conidial-layer, later on a yellow layer of perithecia.--Cordyceps (Chrysalis Fungus, Figs. 118, 119) lives in and destroys insects, and after compassing their death produces the club-formed, generally yellow, stromata, one part of which bears conidia (Isaria) and another perithecia. C. militaris (Fig. 118) on the chrysalides and caterpillars of moths, is the most common.

The so-called Botrytis bassiana, which produces the disease known by the name of “Muscardine,” in silkworms, is probably a conidial form belonging to Cordyceps.

Sub-Family 2. =Sphæriales.=

To this sub-family belong the majority of the Pyrenomycetes. The perithecia are of a firm consistence (tough, leathery, woody or carbonaceous), and of a dark colour. Their covering is quite distinct from the stroma when this structure is present. The stromata are sometimes very large, and may be either cushion-like, crustaceous, upright and club-like, or branched bodies. In general, small, inconspicuous Fungi, living on dead vegetable matter, sometimes parasites. Free conidiophores and conidiocarps are known in many species, and in several, chlamydospore-like forms of reproduction. Orders 3–18 constitute the Sphæriaceæ of older systematists.

Order 1. =Sordariaceæ.=--Fungi living on dung with fragile perithecia, either aerial or buried in the substratum. The dark brown or black spores have either a mucilaginous envelope (Sordaria, etc.) or mucilaginous appendages (Podospora), by means of which their expulsion and distribution are promoted.

Order 2. =Chætomiaceæ.= Perithecia fragile, free, bearing on the summit a tuft of hairs. Chætomium, on decaying vegetable matter.

Orders 3–7. Perithecia scattered or aggregated, situated from the commencement on the surface of the substratum. Stroma wanting.

Order 3. =Trichosphæriaceæ.= Trichosphæria parasitica (Fig. 121), on Abies alba; Herpotrichia nigra on Picea excelsa and Pinus montana.

Order 4. =Melanommaceæ.= Rosellinia quercina lives in the roots of 1–3-year-old Oaks, and destroys the plants.

Order 5. =Ceratostomaceæ.=

Order 6. =Amphisphæriaceæ.= Strickeria obducens (Fig. 120) has brick-like spores, and lives aggregated on the hard branches of Fraxinus.

Order 7. =Lophiostomaceæ.=

Order 8. =Cucurbitariaceæ.= Perithecia tufted, at first embedded, then breaking through, often situated upon an indistinct stroma.

Orders 9–13. The perithecia remain embedded, and are only liberated by the casting off of the covering layers of the substratum. Stroma wanting.

Order 9. =Sphærellaceæ.= The species of Sphærella have colourless, bicellular spores. They live upon the leaves of many plants, and develope spherical perithecia upon the fallen leaves.

Order 10. =Pleosporaceæ.= The conidial-forms of Pleospora herbarum and P. vulgaris form a black covering on various plants, known as “smuts.”--Venturia ditricha occurs on the underside of dry Birch leaves, and perhaps to this belongs the conidial-form, Fusicladium pirinum, which causes the “Rust spots” on Apples and Pears.

Order 11. =Massariaceæ.=

Order 12. =Clypeosphæriaceæ.=

Order 13. =Gnomoniaceæ.= Perithecia, with peak-like aperture. Gnomonia erythrostoma in the leaves of Prunus avium, which turn brown and do not fall in autumn.

Orders 14–18. Stroma generally well developed. The perithecia are embedded in the stroma, but when this is rudimentary, in the substratum.

Order 14. =Valsaceæ.= Valsa.

Order 15. =Diatrypaceæ.= Diatrype.

Order 16. =Melanconidaceæ.=

Order 17. =Melogrammataceæ.=

Order 18. =Xylariaceæ.= This order is the most highly developed of the Sphæriales. The stroma arises on the surface of the substratum, which is generally dead or decorticated wood; it is well-developed, crustaceous, hemispherical or upright. In the younger conditions it is covered with a layer of conidia, and later on it bears the perithecia, arranged in a layer immediately beneath its surface. The ascospores are of a dark colour. Often also there are free conidiophores.

Hypoxylon and Ustulina have a cushion-like or crustaceous stroma.--Xylaria has a club-shaped or branched stroma, often several centimetres high. X. hypoxylon (Fig. 122) and X. polymorpha occur on old tree stumps.--Poronia grows on old horse dung, and has a conical stroma.

Sub-Family 3. =Dothideales.=

The perithecia are always embedded in a black stroma, and are not distinctly separated from it. The accessory forms of reproduction are: conidiophores, conidiocarps, and yeast-like conidia. The majority are parasites. One order.

Order =Dothideaceæ=. Phyllachora graminis produces scab-like patches on the leaves of the Grasses.--Scirrhia rimosa grows on the leaf-sheathes of Phragmites.--Rhopographus pteridis on Pteridium aquilinum.

Family 4. =Hysteriales.=

This family, like the following, has hemiangiocarpic ascocarps (apothecia). These are closed in the early stages, but when ripe open in a valvular manner by a longitudinal fissure; they are black, oblong, and often twisted. Some species are parasites, especially upon the Coniferæ.

Order 1. =Hysteriaceæ.= Hysterium pulicare upon the ruptured bark of many trees.

Order 2. =Hypodermaceæ.= The species of Lophodermium live upon the leaves of Conifers, and are the cause of their falling off (blight). L. pinastri (Fig. 125), on the leaves of Pinus and Picea; the leaves become red-brown and fall off; at first conidiocarps are formed, and later apothecia; L. nervisequium (Fig. 123), on Abies alba; L. macrosporum (Fig. 124), on Picea excelsa; L. brachysporum, on Pinus strobus.

Order 3. =Dichænaceæ.=

Order 4. =Acrospermaceæ.=

Family 5. =Discomycetes.=

The ascocarps (apothecia) are at first closed, and only open at the time of their ripening, not valvularly, but more or less like a saucer or cup, so that the hymenium lies exposed on their upper surface. In the first three sub-families, and generally also in the fourth, the apothecia are formed inside the substratum. The apothecia are, in contrast to the Pyrenomycetes, light and brightly coloured, and their size varies very much, and may be several centimetres in diameter. Paraphyses are often present between the asci; they often contain colouring matter, and give to the disc its characteristic colour. The tissue on which the asci are borne is known as the hypothecium. The shape and colour of the spores is not so varied as in the Pyrenomycetes. The accessory forms of reproduction are conidia (sometimes of two forms), chlamydospores, and oidia. The family is divided into 5 sub-families.

Sub-Family 1. =Phacidiales.=

The apothecia are developed in the interior of the substratum, which they break through, and in general dehisce apically. The envelope is tough and black. Hypothecium inconspicuous; hymenium flat.

Order 1. =Euphacidiaceæ.= Phacidium abietinum, on the leaves of Abies alba.--Rhytisma; the pycnidia are found in the summer on the green leaves, while the apothecia are developed on the fallen leaves and dehisce in the following spring. R. acerinum causes black spots on the leaves of the Sycamore, and R. salicinum on Willows.

Order 2. =Pseudophacidiaceæ.=

Sub-Family 2. =Stictidales.=

The apothecia when ripe break through the substratum which forms a border round them. Hymenium generally saucer-shaped.

Order 1. =Stictidaceæ.= Stictis.

Order 2. =Ostropaceæ.= Ostropa.

Sub-Family 3. =Tryblidiales.=

The apothecia are embedded in the substratum in the early stages, and then are raised high above it. Hypothecium thick. Hymenium cup-shaped.

Order 1. =Tryblidiaceæ.= Tryblidium.

Order 2. =Heterosphæriaceæ.= Heterosphæria patella on the dead stalks of Umbellifers.

Sub-Family 4. =Dermateales.=

The apothecia in the early stages are embedded in the substratum and then break through it, or are from the first situated on the surface of the substratum. Hypothecium thick.

Order 1. =Cenangiaceæ.= Cenangium.

Order 2. =Dermateaceæ.= Dermatea.

Order 3. =Patellariaceæ.= Patellea, Biatorella, Patellaria.

Order 4. =Caliciaceæ.= Calicium, Coniocybe, etc., on the bark of trees.

Order 5. =Arthoniaceæ.= Arthonia on the bark of several trees. Celidium stictarum on the apothecia of Sticta pulmonaria.

Order 6. =Bulgariaceæ.= Apothecia gelatinous under moist conditions, and horny when dried.--Calloria fusarioides; the red apothecia break out in the spring on the dried stalks of Urtica dioica; a gelatinous reproductive form of the Fungus is found before the apothecia, which consists of oidia (formerly described as “Dacryomyces urticæ”).--Bulgaria inquinans on the living or fallen trucks of Oaks and Beeches.

Sub-Family 5. =Pezizales.=

The apothecia are developed on the surface of the substratum and are waxy or fleshy; at the commencement closed, and covered with a saucer- or cup-shaped, seldom flat, hymenium. The hypothecium is generally well developed. This sub-family is the richest in species of the Discomycetes and contains forms of very different habit. They grow upon dead wood, upon the ground, and upon dung. A few are parasites.

Order 1. =Helotiaceæ.= Apothecia with waxy envelope of colourless, or yellowish prosenchymatous cells.--~Chlorosplenium æruginosum is found on decaying wood (particularly Oak and Birch), to which it gives a green colour. Sclerotinia has sclerotia which are developed upon the host-plant and from which, after a period of rest, the long, brown-stalked apothecia arise. S. ciborioides (S. trifoliorum, Fig. 128) is parasitic on Clover; S. sclerotiorum, on Daucus-roots, Phaseolus, etc.; S. baccarum, on the berries of Vaccinium myrtillus; “Botrytis cinerea” is a common parasite and is probably the conidial form of S. fuckeliania (Fig. 127).--Helotium herbarum lives on dry plant stems.--Dasyscypha willkommii (Fig. 129) produces Larch-canker on the bark of the Larch.~

Order 2. =Mollisiaceæ.= Mollisia cinerea, principally on decaying wood.

Order 3. =Pezizaceæ.= This order contains the largest and morphologically the highest forms of the Discomycetes. Apothecia fleshy, and in the later conditions generally saucer-shaped.

Peziza, with sessile apothecia, growing on the ground; P. cochleata is brown, and coiled like a snail-shell; P. coccinea is scarlet; P. aurantia occurs as an orange-coloured expansion on the ground.

Order 4. =Ascobolaceæ.= Apothecia fleshy; in the later stages flat or convex. The asci are, comparatively speaking, large, and often contain a great number of spores which escape by the casting off of a lid on the summit of the ascus. Generally living on dung.--Ascobolus furfuraceus, etc.

Family 6. =Helvellales.=

These Fungi have the appearance of clubs, bells, or mushrooms, consisting of an upright stalk bearing a large and fleshy head, on the exterior surface of which the hymenium is spread. The ascocarps are probably gymnocarpic from the beginning, and on this account these plants are placed in a separate family. The development of the ascocarps is unknown. The Morchella (Morell) grows on the ground; some species are edible. 1 order.

Order. =Helvellaceæ.= Spathulea is yellow and club-shaped, and forms “fairy rings” in woods.--Geoglossum (Earth-tongue) projects above the ground as a black tongue, or as a club-shaped body. Several species are found in meadows and on heaths.--Helvella has a stalk, bearing an irregularly folded head, on the external surface of which is the hypothecium.--Morchella (Morell, Fig. 130), the stalk bears on its summit the conical or spherical head, the external surface of which is reticulate and bears the asci.--Mitrula. Verpa.

APPENDIX TO THE ASCOMYCETES:

Family 7. =Ascolichenes (Lichen-forming Ascomycetes).=

The Lichens were formerly classed among the Thallophyta as a group quite distinct from the Algæ and Fungi. Investigations during the last twenty-five years, however, have conclusively proved that the Lichens are Fungi which reproduce in the same manner as the Ascomycetes, or, more rarely, the Basidiomycetes, and have entered into a peculiar symbiotic relation with Algæ, especially the Cyanophyceæ and Protococcoideæ, with which they associate, and without which they would be unable to exist. The Fungus forms the largest portion of the Lichen, enclosing the Alga with which it may be said to be commensal. The Fungus especially produces reproductive bodies and absorbs the inorganic nourishment through the rhizoids, whilst the Alga supplies it with the organic materials. In consequence of this the Lichens, in contradistinction to other Fungi, need light for the development of their nutritive organs, and are therefore, in any case internally, of a more or less greenish colour. The form and condition of the thallus is unusual among the Fungi, and they can grow upon rocks and in other places where no dead organic matter, such as would be required by other Fungi, is obtainable.

Two cellular forms are therefore to be found in each Lichen:

1. The cells which belong to the Fungus. These are generally septate, branched hyphæ without any trace of chlorophyll. In the thallus of the majority of Lichens there may be found a medullary layer (Fig. 131 m) of loosely-woven hyphæ, between which there are large air chambers; and an external layer (cortex) (Fig. 131 o, u) formed of closely-woven hyphæ without any intercellular spaces. In some Lichens (Collemaceæ) the hyphæ wind about in the thallus, being equally distributed throughout, without forming any decided strata. These Lichens moreover become gelatinous when exposed to moisture (Fig. 132), on account of the swelling of the walls of the Algæ. The hyphæ contain protoplasm with drops of oil, but never starch; their walls easily swell when exposed to damp after having been dried, and in some (e.g. Cetraria islandica) they become gelatinous when cooked. Certain strata of hyphæ become blue on treatment with iodine alone, from which it is inferred that the wall is allied, in its chemical nature, to starch.

2. The enclosed Algæ, termed “gonidia.” Some belonging to the Cyanophyceæ, Protococcoideæ, (especially Pleurococcus) and Chroococcaceæ, are spherical and are found isolated, or in irregular groups of cells (Fig. 131 g); some belonging to Nostoc (Fig. 132 g), Lyngbyaceæ, etc., are placed in cell-rows. Each Lichen, as a rule, has only one definite Algal-form for its gonidium.

The gonidia either lie together in a certain stratum between the cortex and the medullary layer (Fig. 131 g), or are scattered irregularly throughout the entire thallus (Fig. 132). The thallus is in the first instance termed “heteromerous,” in the second instance, “homoiomerous.” The Fungal-hyphæ embrace the gonidia and apply themselves closely to, or even penetrate them, and hence it has been difficult to decide whether the one cellular form does or does not develop from the other (Figs. 134, 135).

This theory regarding the symbiosis of Fungi and Algæ to form a Lichen is termed the Schwendenerian theory, after the first scientist who advanced it with any weight. It had been already indicated by De Bary, and further arguments in its support have at a later time been adduced by Bornet, Stahl, Treub, Frank, Bonnier, Alfr. Möller and others.

The thallus of the Lichen appears mainly under three forms:--

1. The CRUSTACEOUS, which adheres firmly to the substratum (bark, stone) throughout its entire surface, without being raised into any free patches or lobes. It has, in many instances, no definite outline, and hyphal-branches from it often penetrate deeply into the substratum. It grows at the circumference and sometimes dies away in the centre (Figs. 138, 139, 140).

2. The FOLIACEOUS. This also lies flat upon the substratum, but is not firmly attached to and has a definite outline. It grows at the margin, and raises itself a little by free outgrowths and lobes (Fig. 141). The rhizoid-strands spring out from its whitish under surface (Fig. 131, r).

3. The FRUTICOSE, which is attached to its substratum at a small point from which it projects freely, either erect or pendulous. It is more or less tufted, in the form of a bush (Figs. 142, 143). These three thallus-forms gradually pass over by many intermediate forms into one another.

The Lichens, like other Ascomycetes, have very variously constructed ascospores (Fig. 137), which are enclosed in asci (Fig. 136), usually surrounded by paraphyses attached together. Furthermore they possess pycnidia (Fig. 141) containing numerous microconidia. These were formerly considered as organs of fructification, and were termed “spermatia,” and the pycnidia, “spermogonia.” Alfr. Möller proved, in 1887, that the microconidia are able to germinate and produce a mycelium with new conidia, just as in other Ascomycetes.

VEGETATIVE REPRODUCTION takes place by soredia, which to the naked eye appear as whitish powder on the surface of the thallus. They are small round bodies, formed by one or a group of gonidia, which are surrounded by a mass of felted hyphæ. After the rupture of the cortex they are set free, and readily carried by the wind to other places, where under favourable circumstances they establish a new thallus.

GEOGRAPHICAL DISTRIBUTION. The Lichens are the most hardy plants, and are the first to appear on hitherto bare rocks which they gradually disintegrate, and hence prepare the way for the growth of other plants. They are to be found from the Polar regions to the Equator; from the highest snow-free mountain-peaks down to the level of the sea; on the stems of trees; on rocks, soil, some even on inundated places; on stones in woodland streams, and on beaches; but they are never found upon rotten organic remains. Some grow gregariously in enormous masses, and form wide-stretching carpets, e.g. Reindeer Moss (Cladonia rangiferina), species of Cetraria and other fruticose Lichens.

USES. On account of the cell-wall being composed of Lichenstarch (Lichenin), the Iceland-Lichen and Manna-Lichen (Lecanora esculenta) are used as food; the latter grows on stones, in the deserts of Asia and North Africa, and is often torn loose in large masses and carried away by the wind. The Reindeer-Lichen is not only the principal food of the reindeer, but it is also used in the manufacture of Danish brandy. Cetraria islandica (Lichen islandicus) is OFFICINAL. Colouring materials (lacmus, orseille, persio) are made from several species, especially from Roccella tinctoria (from the rocky coasts of the Mediterranean). Parmelia saxatilis and particularly Lecanora tartarea are used for colouring purposes in the Northern countries.

About 2,000 species of Lichens have been described. If we disregard the Basidiolichenes, which will be considered on page 176, the remaining Lichens (Ascolichenes) may be divided into the two following orders according to the structure of the fruit-bodies:--

Order 1. =Pyrenolichenes.= The ascocarps (apothecia) are spherical or flask-shaped, as in the Pyrenomycetes, more rarely linear (Graphis).

According to the nature of the thallus, these Lichens may be divided into:--

a. Thallus homoiomerous, but not gelatinous, branching according to the mode of growth of the Algæ: Ephebe (Fig. 133), with Algæ of the genus Stigonema.

b. Thallus homoiomerous, gelatinous: Lichina.

c. Thallus heteromerous, crustaceous: Verrucaria, Pyrenula; Graphis (Fig. 139), which may be considered as Hysteriaceæ with gonidia; several species of Graphis are common on bark.

d. Thallus heteromerous, foliaceous: Endocarpon.

e. Thallus heteromerous, fruticose: Sphærophorus.

Order 2. =Discolichenes.= These, as in the Discomycetes, have open apothecia, which, as a rule, are cupular, more rarely hemispherical (Cladonia).

According to the nature of the thallus, these Lichens may be divided into:--

a. Thallus homoiomerous, but not gelatinous, branching according to the mode of growth of the Algæ: Cœnogonium.

b. Thallus homoiomerous, gelatinous: Collema (Fig. 132), with Algæ of the genus Nostoc; Leptogium.

c. Thallus heteromerous, crustaceous: Pertusaria (Fig. 140), Lecidea, with apothecia open from the beginning; Lecanora, with apothecia, which in the beginning are closed, later on open, but with a rim formed by the thallus (Fig. 138); Bæomyces, whose apothecia are borne on a stem formed by the thallus.

d. Thallus heteromerous, foliaceous: Parmelia (P. saxatilis; P. parietina, Wall-Lichen, Fig. 141, is yellow, very frequent on tree-stems, stone-walls, tiles); Physcia (P. ciliaris, frequent on tree-stems); Sticta (S. pulmonacea, Lung-Lichen, on tree-stems); Peltigera, especially on the Moss among trees; Umbilicaria, on rocks.

e. Thallus heteromerous, fruticose: Cetraria (C. islandica), “Iceland Moss,” with an olive-brown, flat, furrowed, fringed thallus, on heaths; C. nivalis, white, in the Polar regions; Evernia, Ramalina, Usnea (U. barbata, Beard-Lichen, Fig. 143); Roccella, Stereocaulon, Cladonia, of which the genus C. rangiferina, Reindeer-Moss (Fig. 142) is important; Cladonia has two kinds of thallus, one scaly and leaf-like, the other erect, which bears the apothecia and may be fruticose (Fig. 142), or cupular (Fig. 144); they grow in soil in forests and on heaths.

Sub-Class 2. =Basidiomycetes.=

This sub-class embraces the most highly developed Fungi, with large “fruit-bodies,” which in ordinary language we shortly term Funguses, Toadstools, or Mushrooms.

They have no sporangia, but reproduce only by means of basidiospores, conidia, chlamydospores and oidia. The chief characteristic of this sub-class is the basidium (Fig. 145), i.e. the conidiophore, which has a distinctive form, and bears a definite number (generally 4) of characteristically shaped conidia (basidiospores, Fig. 145 c, d, e).

The summit of each basidium is produced generally into four conical points (sterigmata, Fig. 145 b), from each of which a basidiospore is abstricted. The basidia may be classified into three principal groups, each of which accompanies a distinctive conidiophore: 1, the long, filamentous, transversely divided basidia, with lateral sterigmata and spores, found in the Uredinaceæ (Figs. 146 D, 153), Auriculariaceæ (Fig. 160 B), and Pilacraceæ; 2, the spherical, longitudinally divided basidia of the Tremellaceæ (Figs. 160 C d; 161 iii. iv.); and 3, the ovoid, or cylindrical, undivided basidia of the Autobasidiomycetes (Figs. 145, 163, etc.); the two last have apical sterigmata and spores.

The first two groups are the septate basidia (protobasidia), of the Protobasidiomycetes; while the unseptate basidia (autobasidia) of the Autobasidiomycetes are the third group. On the formation of the basidiospores, the nucleus of the basidium divides into four nuclei, each of which is transferred to a spore.

In addition to the basidia, simple conidiophores are also found. In the Protobasidiomycetes, the simple conidia are very generally found as accessory methods of reproduction in conjunction with the basidiospores; but less frequently in the Autobasidiomycetes, e.g. among the Dacryomycetes, Tomentellaceæ, Heterobasidion annosum.

The simple conidiophores vary in size, and in the number and shape of the conidia; they, however, resemble the basidia, and are doubtless an early stage in the development of the definitely formed basidia.

Finally, well-defined chlamydospores, formed in various ways, appear in the Basidiomycetes as supplementary reproductive bodies (compare p. 90). Among the Protobasidiomycetes, chlamydospores are at present only found among the Uredinaceæ, but in various forms; in the majority of families of the Autobasidiomycetes oidia frequently occur (Fig. 162), but genuine chlamydospores seldom.

In the same species several of the known forms of reproduction may be distinguished.

The mycelium is generally composed of white, branched strands, consisting of numerous felted hyphæ; in some, sclerotia are found.--The great majority are saprophytes; some (particularly all the Uredinaceæ), are parasites.

DIVISIONS OF THE BASIDIOMYCETES.

Series 1. PROTOBASIDIOMYCETES: partly gymnocarpic, partly angiocarpic. „ 2. AUTOBASIDIOMYCETES. Family 1. DACRYOMYCETES: gymnocarpic. „ 2. HYMENOMYCETES: partly gymnocarpic, partly hemiangiocarpic. „ 3. PHALLOIDEÆ: hemiangiocarpic. „ 4. GASTEROMYCETES: angiocarpic. Appended. BASIDIOLICHENES: Lichen-forming basidiomycetes.

Series I. =Protobasidiomycetes.=

To this series belong the lowest of the Basidiomycetes. The basidia appear in two principal forms (1 and 2 on page 144) and are divided into four cells, either transversely or longitudinally, each division forming a sterigma which abstricts a basidiospore. The first three orders, Uredinaceæ, Auriculariaceæ, and Tremellaceæ have gymnocarpic fruit-bodies, while those of the Pilacraceæ, on the contrary, are angiocarpic.

Order 1. =Uredinaceæ (Rusts).= All the Rust-Fungi are parasites, their mycelium living in the interior of the stems and leaves of their hosts, causing red, brown, or black spots--hence their name--and malformations, sometimes of considerable size.

The Rust-Fungi are gymnocarpic and destitute of a hymenium; for these reasons they are regarded as the simplest order of the Basidiomycetes. They are entirely parasitic, and their filamentous, branched mycelium ramifies in the intercellular spaces of its host, and often protrudes haustoria into the cells. The mycelium is perennial should it enter a woody tissue; it may also hibernate in the rhizomes of perennial herbs and permeate the shoots springing from them, but in the majority of the Rust-Fungi the mycelium has a very limited growth. The chief means of reproduction of the Rust-Fungi are the chlamydospores, which in the more highly developed species occur in three forms, namely, the teleuto-, æcidio-, and uredo-spores. The spores, in the host, are formed immediately beneath its epidermis, which is ruptured on the ripening of the spores, with the production of “rust,” brown, red, or black spots. Those chlamydospores which produce basidia are termed teleutospores. The spore on germination produces a transversely divided basidium, “promycelium,” on which basidiospores, “sporidia,” generally four in number, are produced on lateral sterigmata. This basidio-fructification is gymnocarpic; the basidia neither form a hymenium nor a fruit-body (only Cronartium and Gymnosporangium have a slight indication of a basidio-fructification).

Many Rust-Fungi, in addition to basidiospores, have small, unicellular conidia, “spermatia,” which are borne in conidiocarps, “spermogonia.”

The ~TELEUTOSPORES~ (Winter-spores) may be either unicellular or multicellular; in the majority of cases they are enclosed in a hard outer cell-wall, the exospore, which in some cases is very strongly developed; they have also a long or short stalk, the remains of the spore-bearing hypha. Each cell of the teleutospore has one germ-pore (a thin portion of the wall, for the protrusion of the germ-tube; in Phragmidium and Gymnosporangium there are, however, several germ-pores). The colour of the teleutospores is generally much darker than that of the uredospores, and it is by these that the majority of the Rust-Fungi hibernate.

In Gymnosporangium, two kinds of teleutospores are found (distinguished by their size and thickness of exospore). In many species of Puccinia, the form of the teleutospores varies very much, so that in the same layer spores have been observed with the characteristic form of other, allied genera.--The teleutospores of Endophyllum resemble æcidiospores, since they are united in chains, whose cells are easily separated, and are produced in the interior of a “peridium.” The multicellular teleutospores of Coleosporium function as basidia, and from each cell immediately produce basidiospores.--The teleutospores of Coleosporium and Chrysomyxa, differ from other teleutospores in the absence of exospore and germ-pore.

The ÆCIDOSPORES (Spring-spores) are produced in chains which are generally enclosed in an envelope of hyphæ, the peridium; the peridium enclosing the spores being termed the æcidium. The æcidiospores are unicellular, and generally of an orange colour; they are often separated by intermediate cells which wither and so assist in the distribution of the spores. The exospore is made up of minute, radially arranged rods. Generally germination proceeds immediately, the æcidiospore producing a germ-tube, which developes into a mycelium bearing either uredo- or teleutospores.

The æcidia of many Rust-Fungi were formerly considered as distinct genera. The æcidia of Phragmidium, Triphragmium, and Melampsora, in which the peridium is wanting, were in part considered as Cæoma. The æcidia with fimbriate edge, or those of Gymnosporangium with longitudinal lattice-like splits, were considered as “Rœstelia” (Lattice-Rust); large, sac-shaped æcidia on the Coniferæ were known as Peridermium.

The ~UREDOSPORES~ (Summer-spores) are unicellular and arise singly, seldom in chains (Coleosporium). Their colourless, warty exospore bears, in the equatorial plane, 2–8 germ-pores. In the majority, germination proceeds immediately, and a mycelium is produced which at first gives rise to uredospores and afterwards to teleutospores.

The uredospore-formations of Melampsorella and Cronartium are enclosed in an envelope, and hence resemble æcidia.--Between the uredospores sterile, unicellular hyphæ (paraphyses) may be found.

The spermogonia are spherical or pear-shaped conidiocarps, generally embedded in the substratum, and are produced before the æcidia, before or simultaneously with the uredospores, or before the teleutospores. The conidia, as far as observations go, do not generally germinate under ordinary conditions.

Among the Rust-Fungi some species are found which only form basidiospores and teleutospores (Puccinia malvacearum, Chrysomyxa abietis). Other species have in addition uredospores; others spermogonia and uredospores; others spermogonia and æcidia; others spermogonia, uredospores and æcidia. Those species in which all the methods of reproduction are not developed must not be considered as incomplete forms.

As a rule the mycelium, which is produced from the basidiospores, developes æcidia; in the species, however, without æcidia, it developes the uredo-form, and when the uredospores are also absent, the teleutospore-form. It has been established in some species of Puccinia and Uromyces that the formation of æcidia can be suppressed, and it is not a necessary part of the cycle of development of the species.

The majority of Rust-Fungi hibernate in the teleutospore-form. Many species are able to hibernate in the uredospore-form (Coleosporium senecionis). Others pass the winter in the æcidio-form, and develope æcidia on new hosts (Uromyces pisi, on Euphorbia cyparissias; Phragmidium subcorticium, on Rosa; Æcidium elatinum, on Abies alba). In Chrysomyxa abietis, the mycelium, developed from the basidiospores, survives the winter.

Among the Rust-Fungi, with several forms of reproduction, there are about sixty whose development can only be completed by an alternation of hosts, that is, on one host only uredo-and teleutospores are produced, while the further development of the germinating basidiospores, and the formation of the æcidia and spermogonia from its mycelium, can only take place on a second quite distinct and definite host (heterœcious or metoxenous Fungi). Those Fungi which have all their forms of reproduction on the same host are termed autœcious or autoxenous. It is not, however, always necessary that the heterœcious Rust-Fungi should regularly change their hosts; for example, Puccinia graminis can hibernate in the uredo-form on the wild Grasses, and in the spring can distribute itself again in the same form.

As a consequence of the alternation of hosts the various forms of development were considered as independent genera (Uredo, Æcidium, Rœstelia, Cæoma, Peridermium), until De Bary and Oersted established, about the same time (1865), the mutual connection of some forms, and paved the way for the right conception of these Fungi.

As an example of one of the most highly developed species, Puccinia graminis, the “Rust of Wheat,” holds a prominent position. Its uredospores and teleutospores are produced (Fig. 146) on Grasses (on cereals, especially Wheat, Rye, Oats, and many wild Grasses), while the æcidia and spermogonia are confined to the Berberidaceæ. The teleutospores, developed on the Grasses, hibernate on the dried portions of their host, and in the succeeding year each of the two cells of the teleutospore may develop a basidium with four basidiospores (Fig. 146 D, c). The basidiospores are distributed by the wind, germinate quickly, and only proceed to further development on Berberis or Mahonia. The germ-tube bores through the epidermis of the Barberry-leaf, and forms a mycelium in its interior, its presence being indicated by reddish-yellow spots on the leaf. After 6–10 days the flask-shaped spermogonia appear (Fig. 147 B; C, a; conidia in Fig. 147 D) and a few days later the cup-shaped æcidia (Fig. 147 A; C, c, d, e). The former are generally on the upper, and the latter on the under side of the leaf. The orange-coloured æcidiospores scatter like dust, and germinate only on Grasses; the germination takes place in about two days when placed on any green part of a Grass. The germ-tube enters the Grass-leaf through a stoma; a mycelium is developed in the leaf, giving rise to a small, oval, rust-coloured spot (Fig. 146 A); in about 6–9 days the epidermis is ruptured over the red spot, and numerous reddish-yellow uredospores, formed on the mycelium, are set free. The uredospores (Fig. 146 B) are scattered by the wind, and can germinate should they fall on the green portions of other Grasses: they then emit 2–4 germ-tubes through the equatorially-placed germ-pores. The germ-tubes enter a leaf through a stoma, a new mycelium is then developed, and in about eight days a fresh production of uredospores takes place, which germinate as before. The uredospore-mycelium very soon produces, in addition, the brown teleutospores, which give a brown colour to the rust-coloured spots, the familiar uredospores on the cereals being quite suppressed towards the close of the summer (Fig. 146 C, D). The “Rust of Wheat” hibernates on some wild Grasses in the uredospore-form.

GENERA. Puccinia (Fig. 146, 147) has bicellular teleutospores, each having a germ-pore, and the æcidia when present have an indented peridium; some species, as exceptions, have 1–3-celled teleutospores. Many species are HETERŒCIOUS, for example, P. graminis, described above; P. rubigo, which also infests various Grasses, but whose æcidia appear on Anchusa; the masses of teleutospores are small; they contain paraphyses, and are for a long time covered by the epidermis. P. coronata, on Oats and Rye Grass; its æcidia on Rhamnus; the teleutospores are surmounted by a crown--“coronate processes.” P. phragmitis, on Reeds; æcidia on species of Rumex and Rheum. P. moliniæ, on Molinia cœrulea; the æcidia on Orchids. P. poarum, on Meadow-Grass; æcidia on Tussilago. Various Puccinias growing on species of Carex have their æcidia on Urtica, Lysimachia, Cirsium, Pedicularis, etc.--Of those AUTŒCIOUS species, which have all their generations on the same host, may be noted:--P. galii, P. menthæ, P. violæ, P. epilobii, P. asparagi, which grow on the hosts from which they have taken their specific names.--As representative of a group which have spermogonia, uredo-and teleutospores on the same host, but on different individuals, P. suaveolens, on the Field-Thistle, may be mentioned. The spermogonia have a strong odour.--A peculiar group (Leptopuccinia) has only teleutospores, which germinate immediately, and whilst still attached to their living host. To this group belong P. arenariæ, on a number of Caryophyllaceæ; and P. malvacearum, on various Malvaceæ, introduced in 1873 from South America to Europe, where it soon proved very destructive to Hollyhocks.

Uromyces (Fig. 149) differs only from Puccinia in always having unicellular teleutospores. Among this genus both heterœcious and autœcious species are found. To the first group belong U. pisi, whose æcidia are found on Euphorbia cyparissias, and U. dactylidis, whose æcidia appear on Ranunculus; to the second group belong U. betæ, U. phaseoli, U. trifolii.

Triphragmium has teleutospores with three cells (one below and two above), on Spiræa ulmaria.

Phragmidium (Fig. 150) has teleutospores consisting of a row of cells (3–10) arranged in a straight line; the upper cell has one germ-pore and the others four germ-pores placed equatorially. Both this and the preceding genus have large, irregular æcidia without peridia, but often with bent, club-like paraphyses (150 b and c); they are all autœcious, and are only found on the Rosaceæ.

Endophyllum (see above, under teleutospores, p. 147) on species of Sempervivum.

Gymnosporangium (Figs. 152, 154) has bicellular teleutospores collected in large, gelatinous masses formed by the swelling of the long spore-stalks; in each cell 2–4 germ-pores are found. Uredospores are wanting. All the species are heterœcious; the teleutospores appear on Juniperus, the æcidia (Rœstelia) on the Pomaceæ. G. sabinæ, on Juniperus sabina, J. virginiana, etc., has the æcidia (“Rœstelia cancellata”) on Pyrus communis (Figs. 152, 148); G. juniperinum, on Juniperus communis with “Rœstelia cornuta” (Fig. 154 a) on Sorbus aucuparia, Aria nivea (S. aria) and Malus communis; G. clavariæforme on Juniperus communis, the æcidium belonging to it (“Rœstelia lacerata”) on Cratægus oxyacantha.

Melampsora has prismatic teleutospores placed parallel to each other and forming a crustaceous layer; in many species they are divided longitudinally into several cells (Fig. 151). The æcidia, without peridium, belonged to the old genus Cæoma. M. caprearum, on Willows, has the æcidia (Cæoma euonymi) on Euonymus. M. hartigii, on Osiers; the æcidium on Ribes. M. mixta, on Salix repens and Orchids. M. pinitorqua, on leaves of the Aspen, æcidia on Pine branches (Pine shoot fungus); M. populina on Populus monilifera and nigra; M. betulina (Fig. 153), on Birch leaves; M. padi (Fig. 151), on leaves of Prunus padus, developes teleutospores in the epidermal cells; M. lini is the cause of injury to the Flax; M. agrimoniæ.

Calyptospora gœppertiana; teleutospores on Vaccinium vitis idæa; spermogonia and æcidia on Abies alba (Firneedle-Rust).

Coleosporium (Fig. 155) forms its uredospores in reddish-yellow chains; for the teleutospores, see page 147. C. senecionis, on the Groundsel; its æcidium (Peridermium wolffii) on Pine-leaves (Fig. 155 a). Other species on Sonchus, Petasites, Campanula, Rhinanthaceæ.

Chrysomyxa (Fig. 156) has bright red, branched teleutospore-chains; each spore developes a 4-celled basidium. C. ledi, on Ledum palustre; its æcidia on the leaves of the Fir. C. abietis (Fig. 156), without uredo-and æcidiospores; teleutospores on the leaves of the Fir. In the first summer, yellow bands are formed on the leaves, and in the following spring the red cushions of spores.

Cronartium (Figs. 157, 159) has unicellular teleutospores united in numbers to form erect threads or columns; the uredospores are enclosed in a “peridium”; C. ribicola (Fig. 157), on leaves of Ribes (especially Black Currants); its æcidia (Peridermium strobi, or P. klebahni) on the stems and branches of Pinus strobus (Fig. 159), on which it causes great damage; C. asclepiadeum, on Vincetoxicum officinale; its æcidia (Peridermium cornui) on the stems and branches of Pinus silvestris.

To the Fungi of which the æcidium is known, whilst the remaining forms are still undetermined, but which are without doubt heterœcious, belong Æcidium elatinum, which produces the enormous “witches’ brooms” and barrel-shaped swellings on stems and branches of Abies alba; and Æcidium strobilinum (Fig. 158), which attacks Fir-cones, causing all the scales to become covered with clusters of æcidia opening by a lid. Hemileia vastatrix destroyed the coffee plantations in Asia.

Order 2. =Auriculariaceæ.= The long, transversely divided basidia bear laterally 4 long sterigmata with basidiospores (Fig. 160 B) and are united to form an hymenium on the surface of the fruit-body. Parasites or saprophytes.

Auricularia sambucina (Auricula judæ), Judas’-ear, has large fruit-bodies, which may attain the size of several inches, resembling an ear or a mussel shell. In the moist condition they are flesh-coloured, tough and gelatinous, but when dried, become hard, grey and wrinkled; the exterior is covered with short hairs; while the internal surface bears the hymenium. Habitat: stems and branches of old Elder-trees (Sambucus).

Order 3. =Tremellaceæ.= The round, pear-shaped, longitudinally divided basidia bear 4 elongated sterigmata, situated apically, and 4 basidiospores (Fig. 160 C, D), and are united into the hymenium on the surface of the fruit-body. The fruit-bodies are frequently gelatinous and quivering; similar fruit-bodies are also found in the Dacryomycetaceæ and Hydnaceæ. Simple conidiophores, which appear not infrequently in the basidiocarps, before the basidia, are known in many species. Saprophytes.

Exidia has kidney-shaped, oblong basidiospores, and small, hook-like conidia; E. glandulosa, E. albida, etc., on wood.--Craterocolla has conidiocarps; C. cerasi on Cherry-wood.--Sebacina incrustans; the yellow, fleshy, or cartilaginous fruit-bodies are found in autumn covering the ground in moist woods.--Tremella has round basidiospores; T. mesenterica has irregularly-folded, quivering, orange fruit-bodies, about one inch in breadth; T. lutescens (Fig. 161) has orange-yellow conidial-and yellow basidial-layers; T. frondosa has fruit-bodies upwards of a foot in breadth.

Order 4. =Pilacraceæ.= The transversely divided basidia have no sterigmata, but sessile basidiospores, and fill up the cavity of a closed (angiocarpic) fruit-body as a gleba without a regular arrangement (hymenium wanting).

Pilacre fagi on the old stems of the Copper-Beech; P. petersii, on dried branches of the Hornbeam, has stalked, capitate fruit-bodies.

Series 2. =Autobasidiomycetes.=

This second and larger part of the Basidiomycetes is characterised by its more highly differentiated, undivided, club-shaped, or cylindrical basidia, which generally bear 4 (seldom 2, 6, 8) apically-placed sterigmata and basidiospores (Fig. 145). The fruit-bodies are partly gymnocarpic (in the first 3 orders and in some Agaricaceæ), partly hemiangiocarpic (in orders 3–6 of the Hymenomycetes and in the Phalloideæ, the fruit-bodies in these orders are in the young conditions more or less angiocarpic, but later on generally open below and bear the hymenium on the under surface of the fruit-body), partly also angiocarpic (in the Gasteromycetes).

Family 1. =Dacryomycetes.=

The long, club-shaped basidia bear two tapering sterigmata, which develope remarkably large basidiospores (Fig. 162 II, XI) and form gymnocarpic fruit-bodies with hymenium. 1 order:

Order 1. =Dacryomycetaceæ.= This order comprises 4 genera of which the first two develope the hymenium on the whole surface of the fruit-body, but the two last only on its apex.

Dacryomyces: the folded, gelatinous, Tremella-like fruit-bodies break out in winter on dried wood (hedges) in the form of red or yellow drops. D. deliquescens is very common (Fig. 121). The following genera have cartilaginous fruit-bodies.--Calocera (Fig. 162), with club-like, simple, or branched, Clavaria-like, fruit-bodies; the orange coloured fruit-bodies of C. viscosa grow aggregated together on the wood of Conifers.--Guepinia resembles a Peziza, and has the hymenium only on the hollow upper surface.--Dacryomitra resembles a Mitrula (Fig. 162).

Family 2. =Hymenomycetes.=

This family is very rich in species (more than 8000 have been described), and to it belong all the “Mushrooms” and “Toadstools.” The fruit-bodies present very various forms; they are generally fleshy, very perishable, seldom leathery or corky, in the last case often perennial. The basidia are more or less cylindrical and bear generally 4 (seldom 2, 6 or 8) sterigmata and basidiospores. The hymenium in the fully-formed fruit-bodies lies free on the surface: in orders 1 and 2 and a portion of order 6 it is from the commencement exposed, fruit-bodies gymnocarpic; orders 3–6 have hemiangiocarpic fruit-bodies (p. 157). In the first order the basidia (or the hymenium) are developed immediately from the mycelium (Fig. 163); the fruit-bodies of orders 2 and 3 present a higher grade of development, and have between the mycelium and hymenium a special hyphal-tissue, a stroma, which is crustaceous, club-like, or coralloid, etc., and in general bears the hymenium on the largest part of the free, smooth surface. In the forms most highly developed (orders 4–6) a new tissue--the hymenophore--is introduced between the stroma and hymenium, which appears on the under side of the fruit-body in the form of warts, projections, tubes, folds or lamellæ (Figs. 166, 167, 174 bc). Paraphyses are frequently found in the hymenium, among the basidia. In the Hymenomycetes few examples of conidia can be recognised at first. More frequently chlamydospores are found, particularly oidia. The mycelium is richly branched, generally colourless, often perennial; it lives in humus or decaying wood, and is seldom parasitic. The hyphæ generally have clamp-connections and unite, sometimes, to form a rhizomorpha (Fig. 177) or sclerotia with coloured, pseudo-parenchymatous covering.

Order 1. =Tomentellaceæ.= To this order belong the simplest of the Hymenomycetes. The basidia (Fig. 145) arise free and irregularly from the mycelium; a hymenium is entirely absent or very slightly formed (in Corticium it attains its highest development); fruit-bodies are also wanting.--In general they form flaky, membranous or leathery coverings on bark and wood. Some are parasites.

Hypochnus without conidia.--Tomentella with conidiophores; growing on wood or earth.--Exobasidium vaccinii (Fig. 163), a parasite on Vaccinium, Andromeda, Arctostaphylos, and Rhododendron, forms flaky-powdery, white or red coverings and may cause hypertrophy of the parts attacked. E. warmingii is parasitic on Saxifraga; E. lauri causes outgrowths on the stem of Laurus canariensis as long as a finger, which formerly were regarded as aerial roots.--Corticium forms membranous to leathery layers or crusts; C. quercinum on wood and bark, particularly Oak, is flesh-coloured; C. cæruleum has a blue hymenium; C. giganteum on the bark of fallen Pine-trees.

Order 2. =Clavariaceæ.= The hymenium is situated on a stroma, and either completely covers the smooth surface of the more or less fleshy gymnocarpic fruit-body, or is confined to a tolerably well defined upper portion of it (Typhula). Paraphyses absent. The vertical, white, yellow, or red fruit-bodies are roundish or club-like, undivided or richly branched (Fig. 125). Generally on the ground in woods, seldom on tree-stems, etc.

GENERA: Clavaria, generally large Fungi with thick, round branches. C. botrytis has a very thick, tubercular stem with numerous short, flesh-coloured branches: it has an agreeable taste. C. coralloides has a brittle, richly-branched fruit-body (Fig. 164); basidia with two large spores. C. pistillaris consists of a single, undivided club of a yellowish-white colour.--Sparassis has compressed, leaf-like, curled branches; S. crispa has fruit-bodies as large as a white cabbage-head, with an agreeable taste.--Typhula and Pistillaria are small Fungi with filamentous stalks, terminating in a small club. The fruit-bodies of the former often arise from a small, spheroid sclerotium; the latter is distinguished by the basidia bearing only two spores.

Order 3. =Thelephoraceæ.= The hymenium is placed on a stroma and covers the smooth surface of the leathery hemiangiocarpic fruit-body, generally on its under side. The edge of the stroma, which bounds the hymenium, is sometimes especially developed (Stereum). Saprophytes.

GENERA: Thelephora. The fruit-bodies in this genus are brown, very irregularly shaped, and often lobed. The spores too are brown, but in the other genera colourless. The species are found growing on barren soil. T. laciniata (Fig. 165) has imbricate, semicircular, dark-brown pileus, which is jagged at the edge and upper surface. The fruit-bodies are very often raised above the ground, and although this species is not a parasite, yet it destroys young seedlings by growing above and smothering them.--Stereum has a stiffer fruit-body, with a distinct, fibrous, intermediate layer. It grows on bark and wood, projecting like a series of imbricate brackets. S. hirsutum is yellow; its free edge is provided with a number of stiff hairs, the upper surface being divided into a number of zones. S. purpureum has a red-violet hymenium which distinguishes it from the previous species.--Cyphella has a membranous cup- or bell-shaped fruit-body, often borne on a stalk, the concave surface being covered with the hymenium. They are small, white Fungi, growing on Moss and dead stems.--Solenia is closely related to Cyphella; its fruit-bodies are smaller and hairy; they are found clustered together forming a crust-like covering on dead wood.--Craterellus has a large, funnel-shaped fruit-body, the hymenium covering the external surface. C. cornucopioides is shaped like a trumpet or a “horn of plenty.” It is dark-grey, several inches in height, and grows gregariously on the ground in forests. It is distinguished by the basidia bearing only two sterigmata.

Order 4. =Hydnaceæ.= The fruit-body is most frequently fleshy, and varies considerably in shape, the simplest forms being resupinate,[14] the higher ones umbrella-like. The hymenophore is found on the free or downward-turned surface, and always takes the form of soft emergences hanging vertically downwards. The emergencies may be thorn-, awl-, or wart-like. The species are found growing on the soil and on dead wood.

GENERA: Hydnum has subulate, distinct emergences. H. repandum is yellow, the stalk being placed in the centre of the pileus. It is an edible species, and often forms “fairy rings” in woods. H. auriscalpium (Fig. 166) is dark-brown, with stalk placed at the edge of the pileus. It grows on old Fir-cones. H. erinaceus grows on old tree-trunks. The fruit-body is yellow and very large--as big as a human head--with emergences as much as an inch in length.--Irpex has a leathery fruit-body, partly resupinate, partly with free, projecting edge; the under side bears tooth-like emergences which are arranged in rows, and Irpex thus forms a transition to the Agaricaceæ.--Phlebia is entirely resupinate, with radially-arranged folds on the free side, and pectinate border.

Order 5. =Polyporaceæ (Pore-Fungi).= An order very rich in species (about 2000 species are described). The fruit-body is of very different forms--resupinate, projecting like a bracket, hoof-like, or umbrella-shaped. In some it is fleshy and edible, in others leathery or corky, persisting for several years. The hymenophore is situated on the under side of the fruit-body, and consists of wide or narrow tubes or pores, whose inner surface is clothed with the hymenium (Fig. 167). In some fruit-bodies large cavities are to be found, which have arisen as interstices between the labyrinthine curved and reticulate folds. Chlamydospores are known in some species. Conidia occur very rarely. Many species work considerable damage: some as parasites on trees, others by destroying timber.

GENERA. Polyporus (Pore-Fungus). The tubes are narrow, accurately fitted together, and forming a thick layer on the under side of the fruit-body, appearing as a number of fine holes. The fruit-body most frequently resembles a bracket, or is hoof-shaped, with one side growing from a tree-trunk; it is very often perennial, and a new layer of tubes arises in each succeeding period of vegetation. Strata, corresponding to the periodically interrupted growth, are thus formed in storeys one above the other, and are visible on the upper surface of the fruit-body, as well as in the interior, as a series of concentric belts, sometimes as many as half a score or more in number. P. fomentarius (Touchwood) attacks trees, especially the Beech. The spores germinate on wounds from broken branches, and the hyphæ, following the course of the medullary rays, find their way into the interior of the tree, from whence the mycelium spreads upwards, downwards, and peripherally, so that the wood becomes rotten (“white-rot”) and thick felts of mycelium are formed in radial and tangential directions. A dark line, caused by the youngest parts of the hyphæ containing a brown juice, marks the boundary between the rotten and the unattacked parts of the stem (Fig. 168); at places where the mycelium extends to the bark, the cambium becomes destroyed and further growth is arrested, so that longitudinal furrows arise on the stem. It is at these places, too, that the hoof-shaped, ash-coloured fruit-bodies are developed, which may attain a circumference of upwards of 7 feet. The interior of the fruit-body consists of a dried-up, loosely felted, red-brown mass of hyphæ, which has been used for tinder and as a styptic (“Fungus chirurgorum”). P. igniarius has a harder, dark-brown, more rounded fruit-body; it grows in a similar manner, but especially attacks Oaks, Poplars, and Plum-trees, the wood of which becomes rotten, and is called touchwood. P. pini (Trametes pini), (Fig. 170), a parasite on the stems of Pinus, causes a kind of “red-rot” in the stem. P. sulphureus has a soft, cheesy, yellow fruit-body; it produces “rot” in Oaks and Apple-trees. P. officinalis, Larch-fungus (“Fungus Laricis” in Pharmocopœia), grows on Larch-trees in the south-east of Europe. P. versicolor has thin, semicircular fruit-bodies, with zones of various colours on the upper side; it is one of the most frequent species on tree-stems. P. frondosus grows on soil in woods, and consists of numerous aggregated fruit-bodies, which become very large and fleshy. This species is edible. P. perennis also grows on the soil in woods; it is very leathery, with central stalk, and has concentric zones on the upper surface of the fruit-body. P. vaporarius destroys the wood of living Pines (Pinus silvestris) and Firs (Picea excelsa), causing it to become red-brown; in timber this Fungus causes “red-strip” followed by a “dry-rot.” P. squamosus destroys many Walnut-trees, and is also very destructive to Limes and Elms. P. fulvus causes a “white-rot” in Abies alba.

Heterobasidion annosum (Polyporus annosus, Trametes radiciperda, Fig. 169) is characterized by its Aspergillus-like conidiophores. It is a parasite on the Pine, Fir, Birch, Beech, etc., and is the chief cause of a root-disease (red-rot) in Pines and Firs; the fruit-bodies develope a large number of basidiospores; they may be very large and are found just beneath the surface of the soil (on living or dead roots), and exposed to the air (on felled stems and roots, in Scandinavia).

Ptychogaster has cushion-like fruit-bodies, which consist chiefly of chlamydospore-chains, formed of ellipsoidal spores, which alternate with short hyphæ having transverse septa and clamp-connections. The hymenial portion is limited to a small group of tubes. Pt. albus (Oligorus ustilaginoides) grows on stumps of Conifers and forms irregular cushions, at first white and later on brown, which consist almost entirely of chlamydospores.

Boletus (Fig. 171) has a fleshy fruit-body resembling a common Mushroom, with central stalk. The layer of tubes is easily detached from the pileus, and the tubes are easily separable from one another. They grow on the ground in woods. Edible species are: B. edulis, with thick, reticulate stalk; B. scaber, with thin stalk and rough pileus; B. luteus, with a ring on the stalk. B. luridus is poisonous, its tubes have red openings, and the flesh turns quickly blue when broken and exposed to the air.

Fistulina hepatica (Beef-steak Fungus), has a red, fleshy, edible fruit-body, with red juice. The tubes are individually distinct; conidia are also developed. Grows on old Oaks.

Merulius lacrymans (“Dry-rot”) has a resupinate fruit-body with white, cotton-like border, and the remaining portions covered by reticulate, ramified veins of a rust-brown colour. In favourable vegetative conditions it is fleshy and exudes large drops of water--hence its specific name and also the name “Tear Fungus.” The mycelium is at first colourless, and then yellow-brown; when dry it is tough and leathery. It destroys the timber in damp houses, extends far and wide over boards and beams and even over the masonry, giving rise to a disagreeable smell in the rooms in which it lodges. In woods the Fungus lives on Pine-stems. It is brought from the forest on the logs of timber, and is distributed from log to log by the mycelium and the basidiospores. The living mycelium can be recognised by the clamp-connections shooting out branches. The basidiospores are often ejected a distance of a metre; they are elliptical (10–11µ long and 5–6µ broad), and germinate easily on damp wood, or in fruit-juice which has been neutralized with urine or alkaline carbonates.

Dædalea (Labyrinth Fungus), has bracket-like, corky fruit-bodies with irregularly-folded plates or discs on the under side. It forms a transition to the Agaricaceæ. D. quercina is frequent on Oak-stumps.

Order 6. =Agaricaceæ= (=Mushrooms=, =Toadstools=). The hymenophore consists of knife-like plates (lamellæ, gills), which are situated on the under side of the umbrella-like pileus of the fruit-body, and radiate from the central stalk. Those which are first formed extend from the edge of the pileus to the stalk; those formed later reach only a longer or shorter portion of this distance, according to their age. In structure the lamellæ (Fig. 174) consist of a central mass of hyphæ, the trama, continuous with the hyphæ of the pileus; these terminate in a layer of shorter cells, the subhymenial layer, immediately beneath the hymenium which is composed of basidia and paraphyses. In a few species, but not in the majority, the lamellæ are branched, and in some they are decurrent. A few have the stalk placed excentrically, or it may be entirely absent.

In the early stages of its development the fruit-body is more or less enclosed in a hyphal tissue--the “veil” (velum universale, or volva). The veil at first completely encloses the young fruit-body, but is afterwards ruptured as the latter grows, part remaining at the base of the stalk as the “sheath” (annulus inferus), and part on the pileus as scales or warts. In the “Fly Mushroom” (Amanita muscaria) the remains of the veil are especially conspicuous as white patches on the bright red ground of the upper surface of the pileus, and as a sheath at the base of the stalk (Fig. 178 v.). Another veil--the velum partiale--a hyphal tissue (Figs. 178 a; 173) stretches from the edge of the pileus to the stalk, and encloses the lamellæ. This veil is ruptured as the pileus expands, a portion attached to the stalk remaining as the “upper ring” (annulus superus) (Figs. 173, 178 a), or a part attached to the pileus hanging down as a fringe round its edge.--Some genera have no veil, the under side of the pileus being exposed from the first (gymnocarpic Agaricaceæ). Those which have a veil (hemiangiocarpic A.) afford a transition to the angiocarpic Gasteromycetes.

The mycelium mostly grows in soils rich in humus or dung, on decaying trees and similar objects. Many species, e.g. Tricholoma personatum and Marasmius oreades, form the so-called “fairy rings.” The fruit-bodies in these species are confined to a larger or smaller surface on which they are very regularly arranged in a ring. The reason for this is found in the radial growth of the mycelium, so that the oldest portion, or the starting point, is found at the centre of the ring, and the younger ones, on which the fruit-bodies are formed, at the circumference. The older hyphæ gradually die, and at the same time, the radial growth continuing, the ring of fruit-bodies becomes larger and larger. The “fairy-rings” are marked not only by the fruit-bodies, but also by the more vigorous growth and darker colour of the grass upon these spots.

Some species are parasites. An example is presented by Armillaria mellea, a remarkable and very destructive Fungus in woods and forests (Figs. 176, 177). ~In addition to the filamentous, white mycelium, it has also black, or black-brown, horny, root-like mycelium-strands (rhizomorpha) which were formerly considered to belong to a special genus of Fungi described under the name “Rhizomorpha.” The mycelium lives parasitically on the Conifers and other trees, forcing its hyphæ into the bark and between the bark and wood, and thence penetrating into the wood so that the tree is very severely attacked. It may also live saprophytically, and clusters of fruit-bodies are often found on old stumps and stems, on old timber, and in the rich soil of woods. The rhizomorpha, living underground, can extend for considerable distances and infect the roots of neighbouring trees, and spreads in this way the diseases known as “Harzsticken” and “Bark-Canker,” which are very destructive to young trees.~

The chief characteristics by which the numerous genera are separated are the presence or the absence of the two kinds of veils, the nature of the fruit-body, the form, branching of the lamellæ, and their position and relation with respect to the stem, the shape of the pileus, the colour of the spores, etc., etc. A knowledge of the colour may be obtained by placing the pileus with the lamellæ turned downwards on a piece of white or coloured paper, so that the spores, as they fall off, are collected on the paper, and the arrangement of the lamellæ can then be clearly seen.

About 4,600 species belonging to this order have been described.

On account of the large number of species the order is divided into several sections:

1. =Agaricinei=; fruit-body fleshy; lamellæ membranous, knife-like, with sharp edge; basidia crowded together. The FOLLOWING HAVE WHITE SPORES:--Amanita (Fly Mushroom), with volva, and generally also the upper ring on the stalk; many are poisonous, such as A. muscaria (Fig. 178) which has bright red pileus with white spots, A. pantherina and A. phalloides; A. cæsarea is edible.--Lepiota procera (Parasol Fungus) is one of the largest Mushrooms; it has a scaly pileus and moveable ring (edible).--Armillaria mellea has been mentioned above (Figs. 176, 177).--Tricholoma, lamellæ indented near the stalk; T. gambosum (Pomona Fungus) belongs to the best of edible Fungi; T. personatum often forms fairy rings (see above).--Clitocybe, lamella decurrent; C. nebularis is edible.--Pleurotus, stalk eccentric; P. ostreatus (Oyster Mushroom) grows in clusters on tree-stems (edible).--Collybia and Mycena, species numerous, small.--SPORES ROSE-RED: Volvaria and Hyporhodius.--SPORES BROWN: Cortinarius, with cobweb-like veil; Pholiota, membranous veil and ring; P. squarrosa in clusters on tree-stems; P. mutabilis, on tree-stumps (edible).--SPORES VIOLET-PURPLE: Hypholoma, Psalliota; to this section the common edible Mushroom (Fig. 172–174) belongs, with annulus and chocolate-coloured lamellæ; it is cultivated for the sake of the fine flavour.--SPORES BLACK: Coprinarius.

2. =Marasmiei.= Fruit-body tough, almost leathery, and persistent; spores white. Marasmius oreades forms large, regular fairy-rings on pastures and commons; it is used as seasoning in food.--Panus stipticus with eccentrically-placed stalk, in clusters on tree-stumps.--Schizophyllum has the edge of the lamellæ divided longitudinally, and the split portions revolute.--Lentinus affords a transition to Dædalea among the Polyporaceæ.

3. =Russulei.= Fruit-body fleshy and fragile, in which two different systems of hyphæ may be distinguished; spores thorny, white, or pale-yellow. Many are poisonous.--Russula has generally fragile and thick lamellæ reaching from stalk to edge of pileus; pileus frequently red.--Lactarius has white or yellow milky juice, which often is very acid. L. deliciosus has red-yellow milky juice, and is of a pleasant flavour. L. torminosus is poisonous.

4. =Hygrophorei.= Lamellæ thick and waxy, widely separated; spores white. Many species of Hygrophorus have brightly-coloured pileus and grow among the grass on moors and commons.--Nyctalis is parasitic on larger Toadstools. It is remarkable for its abundant formation of chlamydospores, whilst the basidiospores are little developed.

5. =Coprinei.= Fruit-bodies very soft, quickly perishable; lamellæ membranous and deliquescent. The basidia are separated from each other by paraphyses. Coprinus has coal-black spores, grows on manure, and sometimes developes sclerotia.

6. =Paxillei.= Fruit-body fleshy; lamellæ easily detached from the pileus and reticulately-joined near the stalk. They form a connecting link between the Agaricaceæ and Boletus.

7. =Cantharellei.= Lamellæ reduced to dichotomously-divided folds, decurrent on the stalk. Cantharellus cibarius (Fig. 175) is yolk-yellow, and grows on the ground in woods (edible). It is allied to Craterellus.

Family 3. =Phalloideæ.=

The fruit-bodies before they are ripe are spherical or ovoid, and enclosed by a fleshy covering, the peridium, which is perforated at maturity and remains as a sheath (Fig. 179); the fruit-bodies are hemiangiocarpic.

Order 1. =Phallaceæ= (=Stink-horns=). The peridium has a complicated structure and is composed of three layers, the intermediate one being thick and gelatinous. The gleba (the tissue which bears the hymenium) is situated upon a peculiar receptacle which expands into a porous stalk and by its sudden distension, rupturing the peridium, elevates the gleba and hymenium above the peridium, which remains as a sheath. The gleba becomes gelatinous and dissolves away as drops. To this order belong many peculiar and often brightly coloured forms, which are natives of the Southern Hemisphere.

Phallus impudicus (Stink-horn) (Fig. 179), has a fruit-body which at first is white, heavy, and soft, and resembles a hen’s egg in shape and size. The peridium is divided into three layers (Fig. 179 e, g, f) of which the external and internal are membranous, and the middle one very thick and gelatinous; each of these has again a laminated structure. The peridium when ruptured remains as a sheath (k) at the base of the stalk. The receptacle at first is strongly compressed (h) but afterwards expands into a long stalk (l) which bears the conical gleba (m). Prior to the rupture of the peridium the gleba consists of a greenish mass (i) which, when exposed, emits a carrion-like stench serving to attract flies, by whose agency the spores are distributed. It is found commonly in hedgerows and in woods, growing on the ground. The much smaller and less common P. caninus is found on rotten tree-stumps.--In Clathrus cancellatus the receptacle expands into a bright red, reticulate structure. A native of the South of Europe. Colus, Aseroë, Mitromyces.

Order 2. =Sphærobolaceæ.= An intermediate layer of the peridium swells when ripe, becomes convex, and ejects the remaining spherical portion of the fruit-body which contains the spores. Sphærobolus carpobolus has small, spherical fruit-bodies which open in the form of a star.

Family 4. =Gasteromycetes.=

The fruit-body is angiocarpic, fleshy at first, and later generally more or less hard and continues closed after the spores are ripe. The tissue lying immediately inside the peridium is termed the gleba; it is porous, containing a larger or smaller number of chambers lined with the hymenium, which is either a continuous layer of basidia or else it fills up the entire cavity. The basidia as a rule bear four spores, sometimes eight (Geaster), or two (Hymenogaster). The tissue of the walls (trama) consists often (Lycoperdaceæ) of two kinds of hyphæ, some thin and rich in protoplasm, divided by transverse septa and bearing the basidia; others thicker and thick-walled which do not dissolve like the former on the ripening of the spores, but continue to grow and form a woolly, elastic mass, the capillitium, which may be regarded as highly developed paraphyses. The peridium may be either single or double, and presents many variations in its structure and dehiscence. The mycelium is generally a number of string-like strands, living in soils rich in humus.

Order 1. =Tylostomaceæ.= Capillitium present. After the rupture of the peridium the remaining part of the fruit-body is elevated on a long stalk. Tylostoma mammosum, on heaths.

Order 2. =Lycoperdaceæ.= The fruit-body has a double peridium; the external one at length breaks into fragments (Lycoperdon, Bovista), or it has a compound structure of several layers (Geaster) and detaches itself as a continuous envelope from the inner layer, which is membranous and opens at its apex. The interior of the fruit-body consists either solely of the fertile gleba (Bovista, Geaster), or, in addition, of a sterile tissue at the base (Lycoperdon). A capillitium is also present.

Lycoperdon (Puff-ball) has a sterile part at the base of the fruit-body which often forms a thick stalk. The surface of the peridium is generally covered with warts or projections. When young this Fungus is edible, but when ripe it is dry, and used for stopping the flow of blood. L. giganteum, which is often found growing in meadows, attains a considerable size, its diameter reaching as much as eighteen inches. L. gemmatum (Fig. 180) is covered with pyramidal warts; in woods.--Bovista has no sterile basal part; the external peridium is smooth, and falls away in irregular patches. B. plumbea, on links near the sea.--Geaster (Earth-star) has an external peridium composed of several layers, which when the fruit-body opens, split into several stellate segments. These segments are very hygroscopic, and in dry weather bend backwards and so raise the inner peridium into the air. The inner peridium contains the spores and capillitia. G. coliformis has several apertures in the inner peridium. The other species have only one regular aperture at the apex. G. striatus has a pedicellate inner peridium, with conical, striped peristome. G. fornicatus has an external peridium split into four segments. This last and several other species produce “mycorhiza” on the roots of Conifers.

Order 3. =Sclerodermataceæ.= Capillitium wanting. The peridium is simple and thick, gleba with round, closed chambers, which are filled with basidia.

Scleroderma has a corky peridium. The fruit-bodies commence their development under ground. S. vulgare (Fig. 181 V-VII), has a hard, slaty-black gleba.

Order 4. =Nidulariaceæ= (=Nest-Fungi=). Small Fungi of which the fruit-body at first is spherical or cylindrical but upon maturity it becomes cupular or vase-like, and contains several lenticular “peridiola” lying like eggs in a nest. The peridiola are the chambers which contain the hymenium, covered by a thin layer of the gleba, all the remaining portion of the gleba becoming dissolved. On decaying wood.

Nidularia has spherical fruit-bodies containing a large number of lenticular peridiola, embedded in a slimy mass.--Crucibulum has fruit-bodies resembling crucibles with discoid peridiola, each with a spirally-twisted stalk.--Cyathus has a fruit-body, which when open is campanulate, with stratified peridium, and long-stalked, lense-shaped peridiola.

Order 5. =Hymenogastraceæ.= Fruit-bodies tubercular, globose and subterranean, resembling very closely the Truffles, from which they can only be distinguished with certainty by microscopic means. The peridium is simple, capillitium wanting, and the gleba encloses a system of labyrinthine passages covered with a continuous hymenium. The fruit-bodies persist for some time, and form a fleshy mass, the spores being only set free by the decay of the fruit-body, or when it is eaten by animals. The majority are South European. Hymenogaster, Melanogaster, Rhizopogon (Fig. 181 I-IV).

APPENDIX TO THE BASIDIOMYCETES:

Basidiolichenes (Lichen-forming Basidiomycetes).

Several Fungi belonging to the Basidiomycetes have a symbiotic relationship with Algæ exactly similar to that enjoyed by certain Ascomycetes, and these are therefore included under the term Lichens (p. 136). They are chiefly tropical.

Order 1. =Hymenolichenes.= To this order belong some gymnocarpic forms: Cora, Dictyonema, Laudatea.[15]

Order 2. =Gasterolichenes.= To this belong some angiocarpic forms: Emericella, Trichocoma.

APPENDIX TO THE FUNGI.

Fungi imperfecti (Incompletely known Fungi).

1. The =Saccharomyces-forms= are Fungi which are only known in their yeast-conidial form. They are conidia of higher Fungi which can multiply to an unlimited extent by budding in nutritive solutions, and in this way maintain their definite size and shape. The budding takes place only at the ends of the conidia. The wall of the conidium forms at one or at both ends a small wart-like outgrowth, which gradually becomes larger, and is finally separated from its mother-cell as an independent cell, surrounded by a closed cell-wall (Fig. 182 a, b).

Under very favourable conditions multiplication occurs so rapidly that the daughter-cells themselves commence to form buds, before they have separated from their mother-cell, with the result that pearl-like chains of cells are produced. When the yeast-cells have only limited nutriment, with an abundant supply of air, at a suitable temperature, an endogenous formation of spores takes place. The protoplasm of the cells divides into 1–4 (rarely a greater number) masses (Fig. 182 c, d, e) which surround themselves with a thick cell-wall, and in this state can withstand adverse conditions and periods of dryness lasting for several months.

The sporangia are not asci since they have no definite form, and a definite number, form and size of spores is not found. The spores in the different species and kinds occupy varying periods for their development, although exposed to the same temperature, a fact of importance in determining one from another. On germination the wall of the mother-cell is destroyed, and each spore gives rise to a new cell, multiplication taking place by budding (Fig. 182 f). The majority of Yeast-Fungi are able to produce alcoholic fermentation in saccharine fluids.

The most important of these Fungi is the Beer-yeast (Saccharomyces cerevisiæ) with ovate, ellipsoidal or spherical cells (Fig. 182). It is a plant which has been cultivated from time immemorial, on account of its property of producing alcoholic fermentation in sugar-containing extracts (wort), derived from germinating barley (malt). Carbonic acid is also set free during this process. The “surface-yeast” (Fig. 182 a), which produces ordinary beer when the brewing takes place at higher temperatures, has cell-chains; “sedimentary yeast” (Fig. 182 b), used in the brewing of Bavarian beer, has spherical cells, solitary, or united in pairs. Both these and the following Yeast-Fungi include, according to Hansen, several species and kinds.

The “Ferment of Wine” (Saccharomyces ellipsoideus) produces wine in the juice of grapes. Uncultivated yeast-cells are always present on grapes; an addition of this species to the “must” is not necessary to secure fermentation. A large number of other “uncultivated” yeast-cells appear in breweries mixed with the cultivated ones, and cause different tastes to the beer (S. pastorianus, etc.). S. ludwigii, found, for instance, on the slimy discharge from Oaks, produces abundant cell-chains on cultivation. S. apiculatus is very frequently met with on all kinds of sweet fruits, it has orange-like cells. S. mycoderma has cylindrical cells, often united together in chains (Fig. 183): it forms a whitish-gray mass (“fleur de vin”) on wine, beer, fruit-juice, etc., standing in bottles uncorked or not entirely filled. It is thought that this Fungus causes decomposition and oxydises the fluid in which it is found, but it cannot produce alcoholic fermentation in saccharine liquids, and it does not form endospores; hence it is uncertain whether it is true Saccharomyces.

The “Dry-yeast” used in baking white bread is “surface-yeast.” In leaven, a kneaded mixture of meal, barm and water, which is used for the manufacture of black bread, Saccharomyces minor is present, and a species allied to this produces alcoholic fermentation in dough with the evolution of carbonic acid, which causes the dough to “rise.”

2. =Oidium-forms.= Of many Fungi only the Oidium-forms are known, which multiply in endless series without employing any higher form of reproduction. Oidium lactis (Fig. 184) is an imperfectly developed form which frequently appears on sour milk and cheese. It can produce a feeble alcoholic fermentation in saccharine liquids. Thrush or aphthæ (O. albicans) appears as white spots in the mouths of children. Several similar Oidium-forms are parasites on the skin and hair of human beings, and produce skin diseases, such as scurvy (O. schoenleinii) and ringworm (O. tonsurans).

3. =Mycorhiza.= These Fungi, which have been found on the roots of many trees and heath-plants, particularly Cupuliferæ and Ericaceæ, consist of septate hyphæ, and belong partly to the Hymenomycetes, partly to the Gasteromycetes. It has been shown that the Mycorhiza enters into a symbiotic relationship with the roots of higher plants.

DIVISION II.

MUSCINEÆ (MOSSES).

In this Division a well-marked alternation of generations is to be found. The development of the first or sexual generation (gametophyte),[16] which bears the sexual organs, antheridia and archegonia, commences with the germination of the spore, and consists, in the Liverworts, of a thallus, but in the true Mosses of a filamentous protonema, from which the Moss-plant arises as a lateral bud. The second or asexual generation (sporophyte), developed from the fertilised oosphere, consists of a sporangium and stalk.

=The sexual generation, the gametophyte.= The protonema in the Liverworts is very insignificant, and not always very sharply demarcated from the more highly developed parts of the nutritive system. In the true Mosses the protonema is well-developed, and consists of a branched, alga-like filament of cells, the dividing cell-walls being always placed obliquely. In the parts exposed to the light it is green, but colourless or brownish in those parts which are underground (Fig. 186). The protonema is considered to be a lower form of the stem, and grows in the same manner by means of an apical cell; at its apex it may directly develope into a leaf-bearing stem, or these arise from it as lateral branches (Fig. 186 k).

The more highly differentiated part of the vegetative system, the “Moss-plant,” which is thus developed from the protonema, is in the “thalloid” Liverworts generally a dichotomously-branched thallus without any trace of leaf-structures (Fig. 194); in Marchantia (Fig. 197) and others, scale-like leaves (amphigastria) are found on the under surface. The higher Liverworts and the Leafy-Mosses are differentiated into a filamentous, ramified stem with distinct leaves arranged in a definite manner, resembling the stem and leaves of the higher plants (Figs. 186, 195, 200).

True roots are wanting, but are biologically replaced by rhizoids. These are developed on the stems or thallus: in the Liverworts they are unicellular, but in the Leafy-Mosses generally multicellular and branched. In the latter group they are considered identical with the protonema, and may become true protonema, and new plants may be developed from them (Fig. 186 b).

The internal structure of the sexual generation is very simple. The leaves in nearly all cases are formed of a single-layered plate of cells; in the Leafy-Mosses, however, a midrib is very often formed, and sometimes, also, marginal veins; and along these lines the leaves are several layers of cells in thickness. The stem is constructed of cells longitudinally elongated, the external ones of which are narrower and sometimes have thicker walls than the more central ones. Vessels are not found, but in several Mosses there is in the centre of the stem a conducting strand of narrow, longitudinal cells, which represents the vascular bundle in its first stage of development. This strand contains elements for conveying water as well as sieve-tubes. Stomata are entirely wanting in the sexual generation of the Leafy-Mosses; they are found in a few Liverworts (Marchantia), but their structure is not the same as in the higher plants.

VEGETATIVE REPRODUCTION takes place by gemmæ or buds which arise on the protenema, the rhizoids, the thallus, or the shoots, and become detached from the mother-plant; or else the protonema and the older parts of the plant simply die off, and their branches thus become independent plants. This well-developed vegetative reproduction explains why so many Mosses grow gregariously. In certain Marchantiaceæ special cupules, in which gemmæ are developed, are found on the surface of the thallus (Fig. 197 A, s-s). Again, protonema may also arise from the leaves, and thus the leaves may act as reproductive bodies. Certain Mosses nearly always reproduce vegetatively, and in these species the oospheres are seldom fertilised.

The first generation bears the SEXUAL ORGANS; both kinds are found either on the same plant (monœcious), or on separate plants (diœcious). In the thalloid Liverworts they are often situated on the apex of small stems (gametophores), springing from the surface of the thallus. In the Leafy-Liverworts and true Mosses the leaves which enclose the sexual organs often assume a peculiar shape, and are arranged more closely than the other leaves to form the so-called “Moss-flower.” The male sexual organs are called antheridia. They are stalked, spheroid, club- or egg-shaped bodies whose walls are formed of one layer of cells (Fig. 187), enclosing a mass of minute cubical cells, each one of which is a mother-cell of a spermatozoid. The spermatozoids are self-motile; they are slightly twisted, with two cilia placed anteriorly (Fig. 188), while posteriorly they are generally a trifle club-shaped, and often bear at that part the remains of the cytoplasm, the spermatozoid itself being formed from the nucleus. In the presence of water the ripe antheridium bursts, and its contents are ejected; the spermatozoids, being liberated from their mother-cells, swarm about in the water in order to effect fertilisation.

The female sexual organs are termed archegonia. They are flask-shaped bodies (Fig. 189), the lower, swollen portion (venter) having a wall, in most cases from 1–2 cells thick, enclosing the oosphere (Fig. 189 B, k): the long neck is formed of tiers of 4–6 cells, enclosing a central row of cells--the neck-canal-cells (Fig. 189 A). When the archegonium is fully developed, the walls of the neck-canal-cells become mucilaginous and force open the neck of the archegonium. The mucilage thus escapes, and, remaining at the mouth of the archegonium, acts in a somewhat similar manner to the stigma and conducting tissue of a carpel, by catching and conducting the spermatozoids to the oosphere (Fig. 189 B, m), with whose cell-nucleus they coalesce. With regard to the formation of the oosphere, it may further be remarked that the lower part of the archegonium originally encloses the so-called “central cell”; but shortly before the archegonium is ripe, this cuts off a small portion, the ventral-canal-cell, which lies immediately beneath the neck, and the larger, lower portion becomes the oosphere.

The organs mentioned here, antheridia and archegonia, are present in the Cryptogams (Pteridophyta) and the Gymnosperms. They have always the same fundamental structure, but with slight modifications of detail. These plants are therefore known as the ARCHEGONIATA.

The fertilisation of the Mosses cannot be effected without water. Rain and dew therefore play a very important part in this process, and for this end various modifications of structure are found.

Among the sexual organs, paraphyses--filamentous or club-shaped bodies--are to be found.

=The asexual generation, the sporophyte= (Moss-fruit or sporogonium). As the result of fertilisation the oosphere surrounds itself with a cell-wall, and then commences to divide in accordance with definite laws.[17] The embryo (Fig. 189 C) produced by these divisions remains inside the wall a-a of the archegonium (Figs. 190, 199 D, E), and developes into the sporogonium, which remains attached to the mother-plant, often nourished by it, as if the two were one organism. The lower extremity of the sporogonium, the foot (Figs. 190 f; 199 D), very often forces its way deep down into the tissue of the mother-plant, but without an actual union taking place. The central portion of the sporogonium becomes a shorter or longer stalk (seta), while the sporangium itself is developed at the summit. At a later stage, during the formation of the spores, the sporangium very often assumes the form of a capsule, and dehisces in several ways characteristic of the various genera (Figs. 192, 193, 194, 195, 200). The basal portion of the archegonium grows for a longer or shorter period, forming a sheath, the calyptra, in which the capsule is developed, but eventually it ceases to enlarge, and is then ruptured in different ways, but quite characteristically, in each group. Anatomically, the asexual generation is often more highly differentiated than the sexual; thus, for instance, stomata are present on the sporangia of the true Mosses, but are absent in the sexual generation.

As the capsule developes, an external layer of cells--the amphithecium--and an internal mass--the endothecium--are differentiated. As a rule the former becomes the wall of the capsule while the latter gives rise to the spores. In this Division, as in the Pteridophyta, the name archesporium (Fig. 190 t) is given to the group of cells inside the sporangium which gives rise to the mother-cells of the spores. The archesporium is in general a unicellular layer; in Sphagnum and Anthoceros it is derived from the most internal layer of the amphithecium, but with these exceptions it arises from the endothecium, usually from its most external layer. In the true Mosses and in Riccia only spore-mother-cells are produced from the archesporium, but in the majority of the Liverworts some of these cells are sterile and become elaters (cells with spirally thickened walls, Figs. 196, 189), or serve as “nurse-cells” for the spore-mother-cells, which gradually absorb the nutriment which has been accumulated in them. In Anthoceros, and almost all the Leafy-Mosses, a certain mass of cells in the centre of the sporangium (derived from the endothecium) does not take part in the formation of the archesporium, but forms the so called “column” or “columella” (Figs. 190, 191).

The spores arise in tetrads, i.e. four in each mother-cell, and are arranged at the corners of a tetrahedron, each tetrahedron assuming the form of a sphere or a triangular pyramid. The mature spore is a nucleated mass of protoplasm, with starch or oil as reserve material. The wall is divided into two layers: the external coat (exospore) which is cuticularized and in most cases coloured (brown, yellowish), and the internal coat (endospore), which is colourless and not cuticularized. On germination the exospore is thrown off, the endospore protrudes, and cell-division commences and continues with the growth of the protonema (Fig. 186, B-D).

The morphological explanation which Celakovsky has given of the sporogonium, and which is not at all improbable, is, that it is homologous with an embryo consisting of a very small stem-portion and a terminal spore-producing leaf. This will be further explained in the introduction to the Flowering-plants (p. 236).

In the Liverworts the young sporogonium lives like a parasite, being nourished by the sexual generation (only in Anthoceros has it a slight power of assimilation). In the Leafy-Mosses, on the other hand, with regard to the power of assimilation, all transitions are found from abundant assimilation (Funaria, Physcomitrium) to almost complete “parasitism” (Sphagnum, Andreæa). In the majority of the operculate Mosses the sporogonium has a more or less perfect system of assimilation, and is able itself to form a large portion of the material necessary for the development of the spores, so that it chiefly receives from the sexual generation the inorganic substances which must be obtained from the soil. The more highly developed the assimilative system of the sporogonium, the more stomata are present.

APOSPORY. In some operculate Mosses it has been possible to obtain a protonema with small Moss-plants from the seta, when severed from its Moss-plant, and grown on damp sand.

The Mosses are the lowest plants which are provided with stem and leaf. They are assigned a lower place when compared with the higher Cryptogams, partly because there are still found within the Division so many forms with a mere thallus, partly because typical roots are wanting and the anatomical structure is so extremely simple, and partly also because of the relation between the two generations. The highest Mosses terminate the Division, the Muscineæ and Pteridophyta having had a common origin in the Algæ-like Thallophyta.

They are divided into two classes:--

HEPATICÆ, or Liverworts.

MUSCI FRONDOSI. True Mosses or Leafy-Mosses.

Class 1. =Hepaticæ= (=Liverworts=).

The protonema is only slightly developed. The remaining part of the vegetative body is either a prostrate, often dichotomously-branched thallus, pressed to the substratum (thalloid Liverworts), with or without scales on the under side (Figs. 194, 197); or a thin, prostrate, creeping stem, with distinctly-developed leaves, which are borne in two or three rows (Figs. 195, 198), viz., two on the upper and, in most cases, one on the under side. The leaves situated on the ventral side (amphigastria) are differently shaped from the others (Fig. 198 a), and are sometimes entirely absent. In contradistinction to the Leafy-Mosses, stress must be laid on the well-marked dorsiventrality of the vegetative organs; i.e. the very distinct contrast between the dorsal side exposed to the light and the ventral side turned to the ground. Veins are never found in the leaves.

The ventral part of the archegonium (calyptra) continues to grow for some time, and encloses the growing embryo, but when the spores are ripe it is finally ruptured by the sporangium, and remains situated like a sheath (vaginula) around its base. The sporangium opens, longitudinally, by valves or teeth (Fig. 194, 195, 197 b), very rarely by a lid, or sometimes not at all. A columella is wanting (except in Anthoceros, Fig. 194); but on the other hand, a few of the cells lying between the spores are developed into elaters (Fig. 196), i.e. spindle-shaped cells with spirally-twisted thickenings, which are hygroscopic, and thus serve to distribute the spores. (They are seen in Fig. 189 C, not yet fully developed, as long cells radiating from the base of the sporangium. They are wanting in Riccia).

Round the entire archegonium, (or group of archegonia, when several are developed on the same receptacle) a sheath--the involucre--is often formed, which persists, and encloses the base of the stalk of the sporangium, together with the sheath of the archegonium (Fig. 195 p). In the Marchantiaceæ each archegonium is enclosed in a loose investment, the perigynium, which is developed as an outgrowth from the cells of its stalk.

The majority of the Liverworts are found in damp and shady places, pressed to the substratum; a few are found floating in fresh water.

Family 1. =Marchantieæ.=

This embraces only forms with a thallus, which is more or less distinctly dichotomously branched, in some, one or two rows of thin leaves are situated on its under surface. On the upper surface of the thallus are found large air-chambers.

Order 1. =Ricciaceæ.= The sporogonia are, with the exception of a few genera, situated singly on the surface of the thallus, and consist only of a capsule without foot or stalk. They always remain enclosed by the wall of the archegonium (calyptra), and open only by its dissolution. Elaters are not developed. Some genera are found floating like Duckweed.--Riccia glauca grows on damp clay soil. R. fluitans and R. natans float in stagnant waters.

Order 2. =Corsiniaceæ.= (Not native). Intermediate forms between the preceding and the following order. In internal and external structure mainly resembling the Marchantiaceæ. Corsinia; Boschia.

Order 3. =Marchantiaceæ=, are large, fleshy forms. The surface of the thallus is divided into small rhombic areas, in the centre of each of which is found a large, peculiarly constructed stoma (Fig. 197 A); beneath each of these a large air-cavity is to be found. From the floor of the air-cavity a number of alga-like cells project into it; these contain chlorophyll and are therefore the assimilating cells. The antheridia and archegonia are each found aggregated on specially formed branches (somewhat resembling Mushrooms) projecting from the surface of the thallus. The antheridia are developed on the upper surface (Fig. 197 C, D) and the archegonia on the lower (Fig. 197 A, B), near the centrally-placed stalk.

Marchantia polymorpha is diœcious (Fig. 197), and very common on damp places. Lunularia (South Europe), frequently found on flower-pots in conservatories; Preissia, Fegatella, Reboulia, Targionia.

Family 2. =Anthoceroteæ.=

These have an entirely leafless, fleshy, flat, and irregularly-shaped thallus. In its intercellular chambers Nostoc-colonies are often found, which have forced their way through the stomata situated on the under side. The antheridia and archegonia arise from the cells lying inside the thallus. The capsule resembles a long, thin pod; it has two valves and a columella. Anthoceros (A. lævis, Fig. 194, and punctatus).

Family 3. =Jungermannieæ.=

Some forms in this family have a thallus in which leaf-like structures are found (Blasia), while in others (e.g. Metzgeria, Pellia, Aneura) they are entirely absent. The majority, however, have round, thick stems, bearing dorsally two rows of leaves, and one row ventrally. Some of these have the leaves “underlying” (Fig. 195), while in others (Fig. 198) they are “overlying.” (See Figs. 195, 198, with explanation).

The sporangia are spherical, stalked, and situated singly on the apex of the branches, and open by four valves (in Sphærocarpus they are indehiscent).

All the species in this family were formerly reckoned as belonging to one genus, Jungermannia, but now they are divided into several, arranged as follows:--

I. ANACROGYNÆ. The archegonia are situated on the upper side of the thallus or stem, placed laterally, and covered by an “involucre,” formed by the calyptra together with the tissue of the stem or thallus.

a. ANELATEREÆ. Without any elaters: Sphærocarpus, Riella.

b. ELATEREÆ. α. Thalloid: Aneura pinguis, in damp situations; Metzgeria furcata, on trees; Pellia epiphylla, in damp situations; Blasia pusilla, on damp clay soil, in the shade (scales are present on the thallus). β. Foliose and not dorsiventral: Haplomitrium hookeri.

II. ACROGYNÆ. The apex of the stem or of certain branches is adapted for the formation of female shoots. The archegonia are most frequently aggregated on the apex of the shoots, and are encircled by their leaves (perichætium). Between these and the archegonia, enclosing the latter, a peculiar cup-shaped organ (the involucre) is formed. This group only includes leaf-bearing genera: Frullania, Radula, Madotheca, Ptilidium, Calypogeia, Lepidozia, Mastigobryum, Lophocolea, Jungermannia, Scapania, Plagiochila.

Class 2. =Musci frondosi or veri (True Mosses).=

In this class the protonema is well developed, and resembles a branched filamentous Alga, from which it can be easily distinguished by its oblique septa (in Sphagnum it is a cellular expansion). The Moss-plant, which is developed directly from the protonema, generally has an erect, thick, cylindrical stem similarly constructed on all sides. The leaves are arranged spirally, the most frequent divergence being 2/5 or 3/8 (Fig. 200 A). A midrib is often present and also marginal veins formed by longitudinally elongated cells; at these veins the leaf is more than one layer in thickness. In Leucobryum the leaves are generally constructed of more than one layer.

The stem grows by means of a three-sided, pyramidal, apical cell which gives rise to three rows of segments, each segment forming a leaf. The lateral branches arise from the lower portions of the segments, the upper portion of which does not take any part in the construction of the leaf. From their mode of origin the branches are not axillary, and differ in this respect from the Flowering-plants.

The ventral portion of the archegonium is very early ruptured at its base by the growing sporogonium, upon which it remains, and it is thus raised into the air, forming a “hood,” the calyptra (Figs. 192; 200 B). In the Sphagnaceæ the hood is not present; in this order, as in the Liverworts, the archegonium remains at the base of the sporogonium. The sporangium opens by circumsessile dehiscence, the upper portion (operculum) being separated along a specially constructed ring of cells, and falls off like a “lid” (Fig. 200). Only in a few forms (families 2 and 3) does any variation of this take place. Elaters are never found, but (with the exception of Archidium) there is always present in the sporangium a central mass of cells, the columella, which take no part in the formation of the spores. The columella, in some, does not reach quite to the operculum and in these cases the spore-sac is bell-shaped and covers the columella (Andreæa, Fig. 190; Sphagnum, Fig. 199 D); but in the majority of Mosses the columella extends to the lid, so that the space containing the spores becomes a hollow cylinder.

The sporangium is generally raised on a long stalk; in the great majority this stalk is formed from the lower half of the oospore and belongs to the asexual generation--it is then known as the seta. In Andreæa and Sphagnum the seta is very short, and the sporangia are raised upon a long stalk (pseudopodium) developed from the summit of the sexual generation (Figs. 190, 192). In the latter figure an archegonium (a) is seen attached to the pseudopodium, having been carried up with this during the course of its development. The summit of the pseudopodium is enlarged to embrace the foot of the sporogonium (Figs. 192, 199 D).

A. The sporangium is supported on a pseudopodium; the columella does not extend to the operculum.

Family 1. =Sphagneæ (Bog-Mosses).=

The protonema has been already described. The stem is regularly branched owing to the fact that a branch, or collection of branches, arises at every fourth leaf. These branches are closely covered with leaves, some are erect, while others hang down and surround the stem. No rhizoids are developed. These Mosses are of a whitish-green colour, and when water is present are always saturated with it like a sponge, the reason for this being found in the construction of the stem and leaves. The stems are covered by an external layer of large clear cells, without chlorophyll, but with annular or spiral thickenings on the walls, which are also perforated by large holes. By means of capillary attraction, water is thus raised to the summit of the stem. Similarly constructed cells are also found in the leaves, but they are surrounded by a net of very narrow, chlorophyll-containing cells (Fig. 199 F), whose colour is thus to a great extent lost amongst those which are colourless. This anatomical structure is an essential condition for the formation of peat. The Bog-Mosses grow by preference on moors, which they cover with a thick carpet saturated with water. The lower extremities of the plants perish very rapidly, and gradually become converted into peat, and the branches thus separated from each other become independent plants. The sporangia (Fig. 199 D, E) are spherical, but with a very short stalk. They open by a lid, but have no annulus. The archegonium (Fig. 199 C) persists at the base of the sporogonium as in the Liverworts. Only one genus, Sphagnum.

Family 2. =Schizocarpeæ.=

The Mosses which constitute this family are of a brownish-black colour and are found living on rocks. The sporangium resembles that of the Liverworts inasmuch as it opens by four valves, but these continue attached to each other at the apex as well as at the base (Fig. 193).--There is only one genus: Andreæa.

=B.= The stalk is formed from the lower portion of the sporogonium. The columella is continued to the summit of the sporangium and united with it (Archidium has no columella.)

Family 3. =Cleistocarpeæ.=

The fruit does not dehisce in the regular way, but the spores are liberated by decay. They are small Mosses which remain in connection with their protonema until the sporangium is mature. The archegonium remains sessile at the base of the short capsule-stalk, and is not raised into the air (compare Hepaticæ).--Phascum, Ephemerum, Archidium, Pleuridium.

Family 4. =Stegocarpeæ.=

To this belong the majority of the Mosses, about 3,000 species.

The capsule opens as in Sphagnum by means of a lid (operculum), which is often prolonged into a beak. Round the mouth of the opened capsule, a number of peculiar yellow or red teeth are to be found. These constitute the peristome; their number is four, or a multiple of four (8, 16, 32 or 64). The form and thickenings of these teeth are widely different, and on this account are used by Systematists for the purposes of classification. In some Mosses (Fig. 200 C, D) there is a double row of teeth. Except in Tetraphis they are not formed from entire cells, but from the strongly thickened portions of the wall of certain layers of cells belonging to the lid, and persist when this falls off. They are strongly hygroscopic, and assist greatly in the ejection of the lid, in which operation they are considerably aided by a ring of elastic cells with thickened walls, situated in the wall of the lid near the base of the teeth. This ring is known as the annulus. The archegonium is raised into the air like a hood, the calyptra, which either covers the sporangium on all sides (having the shape of a bell), or is split on one side (Fig. 200 B, h).

Among peculiar forms may be mentioned: Splachnum, which is especially remarkable for the collar-like expansion at the base of the capsule. Fissidens deviates in having a flat stem and leaves arranged in two rows. The leaves are boat-shaped and half embrace the stem.--Schistostega has two kinds of stems. The barren ones resemble Fern-leaves; they have two rows of leaves, which are attached together vertically, are decurrent and coalesce at their bases. The fertile ones have an ordinary appearance.--Tetraphis: the peristome is composed of four teeth, which are formed from entire cells. T. pellucida has peculiar gemmæ.

The family is divided into two groups: the Musci acrocarpi, the growth of whose main axis is limited and terminated by the formation of the sexual organs; and the Musci pleurocarpi, whose sporogonia are situated on special lateral shoots, while the growth of the main axis is unlimited.

A. =Acrocarpi.=

Order 1. =Weisiaceæ.= Peristome, with 16 teeth arranged in one series, rarely wanting. Leaf with midrib. Campylopus, Dicranum (D. scoparium, common in forests), Dicranella, Cynodontium.--Weisia, Gymnostomum (no peristome), Systegium.

Order 2. =Leucobryaceæ.= Peristome with 16 teeth. Leaves with three or more layers of cells, of which the external ones are air-conducting and perforated (as in the Sphagneæ), the middle one containing chlorophyll. Leucobryum.

Order 3. =Fissidentaceæ.= Peristome as in the preceding ones. The leaves are arranged in two rows on the plagiotropic shoots; in Fissidens the midrib of the leaf bears wing-shaped outgrowths. Conomitrium, Fissidens.

Order 4. =Seligeriaceæ.= Peristome with 16 undivided teeth. Very small Rock-mosses. Seligeria.--Blindia.

Order 5. =Pottiaceæ.= Peristome with 16 teeth, which are divided almost to the base, or with 32 teeth. Calyptra hood-like.--Barbula (B. muralis, B. ruralis), Trichostomum, Leptotrichum.--Ceratodon purpureus.--Distichium.--Pottia.

Order 6. =Grimmiaceæ.= The leaf-cells are often papillose; in the upper portion of the leaf, small, and of roundish shape. The calyptra is most frequently hood-like or conical. Eucalypta.--Orthotrichum, often with short-stalked capsule, is found on trees.--Coscinodon.--Hedwigia.--Grimmia, Racomitrium.--Cinclidotus.

Order 7. =Schistostegaceæ.= The stems are of two kinds (see above); Schistostega osmundacea, in caves, has a bright emerald protonema.

Order 8. =Splachnaceæ.= The capsule has a large, collar-like neck (see above). Splachnum (especially on manure).

Order 9. =Funariaceæ.= Capsule pear-shaped. Funaria (F. hygrometrica has a very hygroscopic seta, becoming twisted when dry, and straightening with moisture); Physcomitrium; Discelium.

Order 10. =Bryaceæ.= The capsule is thicker towards the apex; most frequently pendulous. Philonotis, Bartramia.--Aulacomnium.--Paludella Meesea.--Mnium.--Bryum, Webera, Leptobryum.

Order 11. =Polytrichaceæ.= Single peristome, formed by 16, 32, or 64 teeth. Leaves with longitudinal lamellæ on upper surface.--Polytrichum has long, hairy calyptra. Catharinea (C. undulata, in forests).

Order 12. =Georgiaceæ.= Peristome with 4 teeth (see above). Tetraphis (T. pellucida has gemmæ).

Order 13. =Buxbaumiaceæ.= Capsule asymmetrical; double peristome: the interior one conical, with 16 or 32 longitudinal folds.--Buxbaumia (B. aphylla); Diphyscium.

B. =Pleurocarpi.=

Order 14. =Fontinalaceæ.= Long, floating Water-Mosses. Fontinalis (F. antipyretica is found in streams). Dichelyma.

Order 15. =Hookeriaceæ.= Pterygophyllum.

Order 16. =Leskeaceæ.= Dull-looking Mosses, with papillose or warted leaves.--Thuidium, Thuja-like with regularly arranged 1–3 doubly pinnate stems; Anomodon, Leskea.

Order 17. =Pterogoniaceæ.= Pterigynandrum filiforme, etc.

Order 18. =Fabroniaceæ.= Anacamptodon.

Order 19. =Neckeraceæ.= Stems most frequently with flat, leafy branches. The leaves are smooth, never with longitudinal folds.--Neckera.

Order 20. =Hypnaceæ.= The leaves are smooth with square, often bladder-like, cells at the edge. Hylocomium (H. splendens, H. triquetrum); Hypnum; Brachythecium; Plagiothecium.--Eurhynchium.--Homalothecium, Isothecium, Orthothiecium, Homalia.--Climacium, Lescuræa, Leucodon.

The Mosses occur all over the globe. Many are found in great numbers, and growing thickly massed together, they form an important feature in landscapes (for example Sphagnum and Polytrichum in the Arctic Tundra). In the Northern and Arctic regions the Mosses are very plentiful, and often form a considerable part of the vegetation, while in the Tropics they are insignificant.

Species of Hypnum and Polytrichum, like Sphagnum, play an important part in the formation of peat.

DIVISION III.

PTERIDOPHYTA (VASCULAR CRYPTOGAMS).

The alternation of generations is as distinct in this Division as in the Mosses, but the sexual generation consists of only a small thallus, the prothallium, which bears directly the sexual organs, antheridia and archegonia; and the asexual generation, which arises from the fertilisation of the oosphere, is no longer a single short-lived sporangium, but a highly developed, generally perennial, plant provided with stem, leaves and true roots (Ferns, Horsetails, etc.), the sporangia being borne on the leaves. In this latter generation the tissues are differentiated into epidermis, ground tissue and vascular tissue; in the last named the bundles are closed, and in the majority of cases concentric.

The =sexual generation=, =gametophyte=, or =prothallium=, is always a thallus, although not always green and leaf-like (Figs. 205, 215, 222, 229, 235, etc.) It is very small, even in cases where it attains the greatest development, and consists only of parenchymatous cells. The prothallium is nourished by hair-like roots (rhizoids) and has only a transitory existence, dying soon after the fertilisation of its oosphere.

The ANTHERIDIA exhibit great variations in structure which, however, must be considered as modifications of the fundamental type which is found in the Mosses. These modifications will be mentioned under the various families. The spermatozoids are always spirally-coiled, self-motile, protoplasmic bodies, with most frequently a large number of fine cilia on the anterior end (Figs. 206, 223, 234). They are formed principally from the nucleus of the mother-cell, and portions of the cytoplasm often remain for a time attached to their posterior end.

The ARCHEGONIA are more uniform throughout the entire Division, and more closely resemble those of the Mosses. They are, as in the previous Division, principally flask-shaped; but the central portion, which encloses the oosphere, is always embedded in the tissue of the prothallium, so that the neck, which is formed of 4 rows of cells, projects above the surface (Figs. 201 ^3, 222 h). The development of the archegonium in a Fern is seen in the accompanying figure (Fig. 201). The archegonium is developed from a surface cell, which divides into three cells by two walls in a direction parallel to the surface of the prothallium (Fig. 201). The most internal cell becomes the ventral portion of the archegonium. The external one (b) divides perpendicularly to the surface of the prothallium into four cells, which again divide parallel to the surface and form the neck (b, in 2 and 3). The intermediate cell projects upwards into the neck and divides into two, the lower one, after the separation of the ventral canal-cell, becoming the oosphere, and the upper one the neck-canal-cell (c, in 2 and 3).

As in the Mosses, the divisional walls of the neck-canal-cells become mucilaginous, causing the rupture of the neck of the archegonium. Fertilisation takes place as in the Mosses, and the passage of the spermatozoids, along the neck, to the oosphere, has been observed. Water (rain or dew) is similarly necessary for the movements of the spermatozoids, and hence for fertilisation. The other classes of the Division chiefly deviate from the Ferns in having the archegonium sunk deeper into the prothallium, and the neck reduced in length (compare Fig. 201 with Figs. 216, 222, 235, 236).

According to the nature of the spores, the three classes of the Vascular Cryptogams are each divided into isosporous and heterosporous groups.

I. The =isosporous= Vascular Cryptogams have only one kind of spore. The prothallium developed from this is in some cases monœcious, bearing both antheridia and archegonia; but in others there is a distinct tendency for each prothallium to bear only antheridia or archegonia (diœcious)--true Ferns and Lycopodium.

In Equisetum there is only one kind of spore, but two kinds of prothallia are developed, one of which bears only antheridia (male), the other only archegonia (female); but the one that bears antheridia may be transformed into the one that bears archegonia and vice versa.

II. In the higher group, =heterosporous= Vascular Cryptogams (Selaginella and Isoëtes, etc.), there are two distinct kinds of spores, the small, microspores, and the large, macrospores. The microspores are male, and produce prothallia which bear only antheridia. The macrospores are female, and produce prothallia which bear only archegonia.

Corresponding to this difference in the spores, there is also found a difference in the development of the prothallium. In the Isosporeæ the prothallium is large, and either green, leaf-like, and provided with rhizoids (most of the Ferns, Horsetails, etc.), or subterranean, pale-coloured, and globular (Ophioglossum, Lycopodium). It lives vegetatively for a fairly long time, and generally produces a large and varying number of archegonia and antheridia. The prothallium in the Heterosporeæ is gradually more and more reduced, its independent and vegetative life becomes of less and less importance, it becomes more dependent on the mother-plant, and projects from the spore very slightly, or not at all. The antheridia and archegonia become reduced in number to one, and also degenerate in point of development.

It may here be remarked that the gradual development of the asexual generation, the development of the two kinds of spores, and the progressive reduction of the prothallium and sexual organs which is found in this Division, is continued to the Gymnosperms and Angiosperms. The microspores are in these called pollen-grains, and the male prothallium is very rudimentary. The macrospores are termed embryo-sacs, and the female prothallium, the endosperm.

The =asexual generation=, =sporophyte=. When the oosphere, which in this case as in all others is a primordial cell, is fertilised, it surrounds itself with a cell-wall and commences to divide into a number of cells, to form the embryo.

The first dividing wall (basal wall) is nearly horizontal, and in the direction of the longitudinal axis of the archegonium. The next wall is vertical, and the next perpendicular to the other two. The oosphere, therefore, is now divided into eight octants by these three walls. The basal wall divides the embryo into a hypobasal and an epibasal half. From the first one, by continued divisions, the first root is developed; from the latter, the stem and leaves. After the formation of the octants the development proceeds in somewhat different ways in the various classes. In addition to the stem, leaf, and root, a “foot” is developed from the hypobasal half which remains enclosed in the prothallium, and conveys nourishment from the prothallium to the young plant until it is able to sustain itself (Fig. 202). The formation of these members in the embryo depends on the position of the oosphere in the archegonium and prothallium, and is independent of gravity.

In the Mosses the asexual generation is the sporogonium, which is limited in its development and in a great measure dependent upon the sexual generation, upon which it is situated; but in the Pteridophyta this generation is an independent and highly developed plant, provided with stem, leaf, and true roots, and has in many instances an unlimited development. The Pteridophyta are the lowest Division with true roots. The root which is first formed is very similar in nature to the primary root of the Monocotyledons; it very soon dies and is replaced by others which are more permanent, and developed upon the stem (adventitious roots); roots are wanting in Salvinia, Psilotum, and some Hymenophyllaceæ. The differentiation is, however, not so complete as in the Flowering-plants, and so many leafy forms are not found. The various members of these plants are anatomically much higher than in the Mosses, having an epidermis, a ground tissue with variously differentiated cells, and a highly developed vascular system. The vascular bundles, like those in the Monocotyledons, are without cambium, and closed; they are therefore incapable of any increase in thickness. In general the bundles are concentric, with the bast round the wood (Fig. 203). The wood is almost entirely made up of scalariform tracheides.

In Isoëtes a secondary thickening takes place by a cambium, which is formed inside the cortex, constructing secondary cortex to the exterior, and secondary wood towards the interior.--Botrychium has also a thickening growth. Collateral vascular bundles occur in Osmundaceæ, Equisetaceæ, and the leaves of many Polypodiaceæ, etc.

It is a point of special interest, that the gigantic forms of Ferns, Equisetums, and Club-Mosses (which flourished in earlier geological periods, when these classes attained their highest development) possessed some means of increasing in thickness.

The sporangia are in all cases capsule-like, and burst open when ripe to eject the spores. They are nearly always situated on the leaves (in Lycopodiaceæ, in the axils of the leaves, or above these, on the stems themselves). In some forms (LEPTOSPORANGIATÆ), the sporangia are developed from a single epidermal cell; in others (EUSPORANGIATÆ), from a group of epidermal cells, or from cells which lie beneath the epidermis. In the first group a primitive mother-cell (archesporium) is formed, which divides commonly into sixteen special mother-cells. In the latter group, on the other hand, a number of primitive spore-mother-cells are developed. In each sporangium three different tissues are generally developed; an innermost sporogenous one (s in Fig. 204 A), which arises from the archesporangium; an outermost one, which forms the wall (a), and may be one or, more rarely, several layers in thickness; and an intermediate one, the tapetum (Fig. 204 A, B, b t), which is rich in protoplasm, and whose cells are dissolved so that the spores float freely in the fluid thus provided. The spores arise as in the Mosses (in tetrads), by the cross-division of the special mother-cells, and according to the manner in which they are arranged in the mother-cell have either a tetrahedral form, with a large base resembling a segment of a ball, or are oblong (bilateral spores). Their construction is the same as in the Mosses (p. 187).

The spore-formation in its earliest commencement takes place in the same way in the Isosporous and the Heterosporous Vascular Cryptogams; but from a certain point, after the tetrahedral division, a difference occurs with regard to the macrosporangia. All the spores formed in the microsporangium may complete their development; but those which are formed in the macrosporangium are generally aborted, with the exception of one or four, and these consequently attain a much larger size (see Fig. 239.--The series to the left are microsporangia; those to the right, macrosporangia).

APOGAMY. In some Ferns (Pteris cretica; Aspidium filix mas, var. cristatum; A. falcatum; Todea africana) the young plant is not developed as a consequence of fertilisation, but as a bud from the prothallium. This is known as apogamy, or loss of the power of sexual reproduction. The antheridia are generally more or less developed; archegonia are entirely wanting in Asp. filix mas, var. cristatum. This variety has probably only become apogamous through cultivation. Many specimens of Isoëtes lacustris, in a lake in the Vosges mountains, produce in the place where the sporangia are usually found, a vegetative shoot which grows into a new plant, so that the sexual generation is wanting in this case. Some specimens have sporangia on some leaves, and shoots on others.

Apospory, or the formation of prothallia instead of sporangia and spores on the leaves, is found in Athyrium filix femina, var. clarissimum. In this case the development of the sporangia proceeds only to a certain point, and from these arrested sporangia the prothallia are produced. Normal sporangia are entirely wanting in this variety, and in Aspidium angulare, var. pulcherrimum, sporangia are completely wanting. Compare the Mosses (page 188).

The Vascular Cryptogams are divided into three large classes, in each of which a progressive development can be traced from the isosporous to the heterosporous forms, but some of these are now only known as fossils.

Class 1. =Filicinæ= (=Ferns=).--The stem is small in comparison with the leaves, and branches only seldom, and then by lateral shoots. The leaves are scattered, large, often deeply divided, and of various highly developed forms. The undeveloped leaves are rolled up in the bud, having what is termed circinate venation. The sporangia are situated on the edge or on the lower side of the leaves, those on which the sporangia are borne (sporophylls) being often the ordinary foliage-leaves; but in a few cases the fertile differ from the barren ones (a higher stage in development). The fertile leaves are not confined to definite parts of the shoot, and do not limit its growth. The archesporium is most frequently unicellular.

A. =Isosporous=: Sub-Class 1. Filices (True Ferns).

B. =Heterosporous=: Sub-Class 2. Hydropterideæ (Water Ferns).

Class 2. =Equisetinæ= (=Horsetails=), in its widest meaning.--The leaves in this class are small in comparison with the stem. They are arranged in whorls, and unite to form a sheath. The sporangia are situated on specially modified, shield-like leaves, which are closely packed together and form a “cone.” The cone is borne terminally, and limits the growth of the shoot. The sporangia are developed from a large group of epidermal cells, the archesporium being unicellular. The branches are arranged in whorls, and develope acropetally.

A. =Isosporous=: Sub-Class 1. Equisetaceæ. Existing forms.

B. =Heterosporous=: Sub-Class 2. Extinct forms.

Class 3. =Lycopodinæ= (=Club-Mosses=).--Roots generally branching dichotomously. The leaves are scattered or opposite, and in proportion to the stem very small, undivided, and simple. They are scale-like and triangular, tapering from a broad base to a point. The sporangia are situated singly (except in Psilotaceæ), and almost in every case on the upper side of the leaf or in the axil of a leaf; but in some cases they are borne on the stem, just above the leaf-axil. The sporangia arise from groups of epidermal cells. The sporophylls are often modified, and differ from the foliage-leaves; they are then arranged in cones placed terminally on branches, thus limiting their growth.

A. =Isosporous=: Sub-Class 1. Lycopodieæ.

B. =Heterosporous=: Sub-Class 2. Selaginelleæ.

Class 1. =Filicinæ= (=Ferns=).

The characteristics of this class have already been given on page 204.

The class is divided into two sub-classes:--

1. The TRUE FERNS, FILICES, have one kind of spore which generally developes monœcious prothallia, relatively large and green. The sporangia are most frequently situated in groups (sori), which are often covered but not enclosed by an indusium.

2. WATER FERNS, HYDROPTERIDÆ, have microsporangia with many (4 × 16) microspores, and macrosporangia, each with one macrospore. The prothallium is small, and projects but slightly from the germinating spore. The sporangia are situated in groups (sori), which are either enclosed by an indusium, or enveloped in a portion of a leaf, to form “fruits” termed sporocarps.

The old name for the Hydropterideæ, “Rhizocarpeæ,” i.e. the “root-fruited,” originated from the erroneous supposition that the sporocarps were borne on the roots.

Sub-Class 1. =Filices= (=the True Ferns=).

Of the eight orders (with about 4,000 species) comprised in this sub-class, the Polypodiaceæ is the largest (having about 2,800 species) and the most familiar; for this reason it will be taken as typical.

=The sexual generation.= When the spore germinates, the external covering (exospore) is ruptured, as in the Mosses. The internal cell-wall (endospore) grows out as a filament, which soon divides and gives rise to the prothallium, a flat, cellular expansion resembling the thallus of a Liverwort. In its fully developed state the prothallium is generally heart-shaped, dark green, and provided with root-hairs, and it attains a diameter of about one centimetre (Fig. 205). It is formed of one layer of cells, except along the central line near the anterior depression, where it becomes several layers of cells in thickness, forming the “cushion,” on the lower side of which the archegonia are developed. The antheridia are first formed; they are thus found on the oldest parts of the prothallium, on its edge, or among the root-hairs. The archegonia are developed later, and are therefore found near the apex. Several tropical Ferns have prothallia[18] deviating from this typical form; Trichomanes (Order Hymenophyllaceæ) has filamentous, branched prothallia, which resemble the protonema of a Moss. Others, again, have strap-shaped prothallia, which resemble the thallus of certain Liverworts.

The ARCHEGONIA have been already mentioned (p. 199, Fig. 201). The ANTHERIDIA are hemispherical or slightly conical bodies (Fig. 206). They consist, as in the Mosses, of a wall formed by one layer of cells, which encloses a number of spermatozoid-mother-cells (A and B). The antheridia when ripe absorb water, and are ruptured, and the spirally-coiled spermatozoids liberated (Fig. 206 S). The spermatozoids have been observed to pass down the neck of the archegonium, and to fuse with the oosphere.

=The asexual generation.= The first leaf, the “cotyledon,” of the embryo developed from the oospore (Figs. 202, 205) is always small, and has a very simple shape. The leaves which occur later become more perfect, stage by stage, until the permanent form of leaf has been attained.--The STEM is most frequently a subterranean or a semi-aerial rhizome; it is only in the tropical, palm-like Tree-Ferns, that the stem raises itself high in the air and resembles that of a tree, with leaf-scars or with the remains of leaves attached (Figs. 207, 203); in certain species the stem is encased in a thick mat of aerial roots (Dicksonia antarctica). When the rhizome is horizontal the internodes are frequently elongated, and the leaves are arranged in two rows, as in Polypodium vulgare and in the Bracken-Fern (Pteridium aquilinum), etc.; it is also generally dorsiventral, having a dorsal side on which the leaves are situated, and a ventral side, different from the former, on which the roots are borne. When the stem ascends in an oblique direction, or is nearly vertical, its internodes are extremely short, and the leaves are arranged in a spiral line with a complicated phyllotaxis, e.g. in Athyrium filix-fœmina, Aspidium filix-mas, etc. The BRANCHING upon the whole is extremely slight, and is generally confined to the petiole (e.g. Aspid. filix-mas), or to the stem near the insertion of the leaves. Several species normally form buds on different parts of the lamina. The buds which are formed on the stem are not confined to the leaf-axil as in the higher plants. The Tree-Ferns, generally, do not branch at all.

The VASCULAR BUNDLES are concentric, with the wood surrounded by the soft bast. In transverse section they are seen as circles or irregularly-shaped figures (Fig. 203), the name of “King Charles and the Oak” (Bracken-Fern) having originated from the appearance which the bundles present in oblique section. In Osmunda they are collateral and resemble those of the Flowering-plants. Round each individual bundle is often a sheath of thick-walled, hard, brown, sclerenchymatous cells, which act as a mechanical tissue; similar strands are also found in other parts of the stem.

The LEAVES in nearly all species are only foliage-leaves, borne in a spiral. They have an apical growth which continues for a long time, and some require several years for their complete development. In the buds they are rolled up (circinate); not only the midrib, but also all the lateral veins, and even the terminal portions of a leaf are sometimes rolled up together, the tissues of the leaf being already fully developed and only waiting to expand. The leaves are often excessively divided and compound, with pinnate branches, and have an epidermis with stomata and a well-developed system of venation. Stipules are only found in Marattiaceæ and Ophioglossaceæ.

Very often peculiar hairs or scales (paleæ, ramenta), dry, brown, flat and broad, are found on stem and leaf.

The SPORANGIA are small, round capsules, which, in a very large number of Ferns, are formed on the back, but more rarely on the edge of the ordinary foliage-leaves. It is very seldom that there is any difference in form between the barren foliage-leaves and the fertile leaves, as is found for example in Blechnum spicant or Struthiopteris; or that the fertile part of the leaf is differently constructed from the barren portion of the same leaf, as in the Royal-Fern (Osmunda). In such instances the mesophyll of the fertile parts is poorly developed.

The sporangia in the Polypodiaceæ are lens-shaped, with long stalk (Fig. 211 D): their wall consists of one cell-layer on which a single row of cells, passing vertically over the top (that is along the edge of the sporangium), is developed into the “ring” (annulus). The cells of the annulus are very much thickened on the inner and side walls, and are yellowish-brown. The thickened cells, however, do not entirely encircle the sporangium, and on one side, near the stalk, they pass over into large, flat, thin-walled cells. These form a weak point in the wall, and it is here that the sporangium is opened diagonally by the elongation of the annulus. The sporangium of the Polypodiaceæ opens as it dries. The cells of the annulus are very hygroscopic, and in straightening, the annulus bends back with a jerk, thus ejecting the spores to considerable distances. The cells of the annulus absorb water with great readiness. [The sporangium arises as a single epidermal cell, from which a basal stalk-cell is cut off. Three oblique cell-walls, intersecting near the base, are next formed in the upper cell, and a fourth between these and parallel to the free surface; an inner tetrahedral cell enclosed by four others is thus formed, the outer cells become the wall of the sporangium, while the inner cell, by a series of walls, parallel to its sides, cuts off a layer of cells which eventually form the tapetum, the remaining central cell constituting the archesporium.]

The SPORES are either oblong and bilateral, or they are tetrahedric with curved sides, depending upon the way in which the tetrad division has taken place.

The sporangia are almost always situated on the nerves and gathered into groups, sori, which differ in form in the various genera. The sori, in many genera, may be covered by a scale-like structure, the indusium (Figs. 211 B, 212).

In the majority of cases, each sorus is situated on a small papilla (placenta, or receptacle), which is supplied by a small vascular bundle. Between the sporangia, hairs (paraphyses) are often situated, which spring either from the placenta or from the stalks of the sporangia.

=Systematic Division.= The Ferns may be divided into two groups, characterized by the structure and development of the sporangia. The sporangia in the EUSPORANGIATÆ take their origin from a group of epidermal cells, and their walls are formed by several layers of cells. The archesporium is the (not tetrahedric) hypodermal terminal cell of the axial row of cells which give rise to the sporangium. In the LEPTOSPORANGIATÆ the sporangia are developed from single epidermal cells, and their walls are uni-layered. The archesporium is a central, often tetrahedric cell, from which sixteen spore-mother-cells are developed.[19] It is difficult to say which form is the oldest (according to Prantl, those which have the sori on the nerve-endings); however, the Eusporangiatæ would seem to have made their appearance long before the others, and also well defined Marattiaceæ and Ophioglossaceæ occur in the Kulm and Coal period, before the true Polypodiaceæ.

About 4,000 species of Ferns are now existing, and they are found especially in tropical and sub-tropical forests.

Family 1. =Eusporangiatæ.=

Order 1. =Ophioglossaceæ.= The prothallium differs from that of all other Ferns in being subterranean, free from chlorophyll, pale and tuberous. The stem is extremely short, with short internodes, most frequently unbranched, vertical, and entirely buried in the ground (Fig. 208 st). In several species (among which are the native ones) one leaf is produced every year, which has taken three to four years for its development. In Botrychium a closed, sheath-like basal part of each leaf covers the subsequent leaves during their development. In Ophioglossum and others each leaf has at its base an intrapetiolar, cap-like sheath, which protects the succeeding leaf. The leaves are of two kinds: (a) foliage, which in Ophioglossum vulgatum are lanceolate and entire, but in Botrychium however, are pinnate (b in Fig. 208 A, B); and (b) fertile, which are found facing the upper side of the foliage-leaves. These latter in Ophioglossum are undivided and spike-like (Fig. 209 A), but pinnate in Botrychium (Fig. 208 B). Each foliage and fertile leaf are branches from the same petiole. The large sporangia are placed laterally, and open by two valves. No annulus is formed (Fig. 209).--Ophioglossum reproduces vegetatively by adventitious buds on the roots.

Three genera with about twelve species.

Order 2. =Marattiaceæ= are tropical Ferns, whose gigantic leaves resemble those of the Polypodiaceæ, but have stipules in addition. The sporangia are grouped in sori, situated on the lower side of the leaves, the sporangia in each sorus being arranged either in two rows or in a ring. In Angiopteris they are isolated (Fig. 210 A), but in the other species (Kaulfussia, Danæa, Marattia), they are united, and form “synangia” divided into a number of chambers corresponding to the sporangia. These open by clefts or pores. Marattia presents the highest development, as its sporangia are completely united in a capsule-like synangium, which is closed until maturity, and then opens by two valves. In each valve there is a row of three to eleven sporangia, each opening by a slit towards the inside (Fig. 210 B, C). An indusium encloses the sorus, except in Kaulfussia; it is formed of flat and lobed hairs, which resemble the hairs of the other portions of the leaves. In Angiopteris and Marattia the indusium is very rudimentary; in Danæa it forms a kind of cupule.

The numerous fossil Marattiaceæ (15 genera, with 98 species) present similar differences to those now living, but more various forms are found, for example, with solitary free sporangia. Those now living are the last small remnant (4 genera with only 23 species) of a once dominant family, which existed from very early times, and whose culminating point was reached in the Kulm and Coal periods.

The Ophioglossaceæ appear also in the Kulm and Coal periods, and were about as numerous as at the present time (presumably 2 genera, with 19 species). Leptosporangiate Ferns appear however to have occurred first of all in the Trias-formation.

Family 2. =Leptosporangiatæ.=

Order 1. =Polypodiaceæ.= Sporangia on the lower side of the leaves, stalked and provided with a vertical, incomplete annulus; dehiscing by a transverse cleft (Fig. 211 D).--The genera are distinguished by the form of the indusium and the position of the sori, etc.

1. The sporangia cover the entire lower surface of the leaf (Tropical America and Asia). Acrostichum, Platycerium.

2. Sori without indusia, circular or oval. Polypodium (Fig. 211 A). The leaves are most frequently situated in two rows on the dorsal side of the creeping rhizome, and fall off leaving a smooth scar behind.--P. vulgare, common in woods, on stones. (Phegopteris also has no indusium; see page 214).

3. The sporangia are situated in continuous lines just inside the margin of the leaf.--Pteris[20]: the sporangia form a continuous line along the entire margin of the leaf (Fig. 211 C), which bends over and covers the sporangia, forming a “false-indusium.” Pteridium has linear sori situated on a marginal vascular bundle, covered by two linear basal indusia, of which the outer is bent over like the edge of a leaf.--P. aquilinum (Bracken) has a wide-spreading rhizome with large alternate leaves, placed on opposite sides, at some distance apart. Only one leaf is developed from each branch every year.

Adiantum (Maiden-hair): sori on the underside of small portions of the edge of the leaf, which are bent over (false indusium). Cryptogramme (Allosorus), Cheilanthes.

4. The sori are oval or linear, situated on one side of the vascular bundle.--Asplenium (Fig. 212 A): sori linear; indusium with one of its edges attached at the external side. A. ruta muraria (Wall-Rue); A. septentrionale; A. trichomanes.--Athyrium: sori linear or curved; A. filix-fœmina (Lady-Fern).--Scolopendrium (Fig. 212 B): sori as in Asplenium, but situated in pairs across the lanceolate, entire leaves. Each sorus is covered on the external side by an indusium, whose free edges are parallel and approach each other. S. vulgare (Hart’s-tongue).--~Blechnum (B. spicant, Hard Fern; the fertile leaves differ from the barren, the pinnæ being narrower, while the underside is almost entirely covered with sori, and hence they are of a much darker brownish hue than the barren ones).--Ceterach: indusium rudimentary or absent.~

5. Sori circular and covered by a shield-like, or reniform indusium.--Aspidium (Fig. 211 B); the leaves wither away and leave no scar upon the root-stock. A. filix-mas (Male-Fern); A. spinulosum.--Phegopteris has no indusium, the withered bases of the leaf-stalks are persistent; P. dryopteris and P. polypodioides.

6. The indusium is situated below the sori, and has the shape of a one-sided scale (Cystopteris, Struthiopteris), or of a cup or cupule, which in Woodsia is sometimes fimbriate (Fig. 212 C, D).

7. The sori are situated on the margin of the leaf, and at the end of a vascular bundle. Indusium, semi-cupular. Davallia. Principally tropical species. 1 in S. Europe.

This order is the greatest, comprising about 2,800 species, the majority being perennial plants. A few are large, and known as Tree-Ferns.

As plants in conservatories and rooms the following are cultivated: species of Gymnogramme (tropical America), Lomaria, Nephrolepis, Pteris (P. serrulata, cretica).

Officinal. Aspidium filix-mas, rhizome and the withered petioles.--Species of Alsophila and Cibotium give Penghawar Djambi. The rhizome of Pteridium aquilinum, var. esculentum, contains so much starch that it is used as food.

The other orders of true Ferns deviate from the Polypodiaceæ, especially in the formation of the annulus, the bursting of the sporangium and its mode of attachment and development, and in the differences in the formation of the prothallium, etc. The principal are:--

Order 2. =Hymenophyllaceæ.= To this order belong the lowest and most Moss-like Ferns; the leaves, with the exception of the veins, are most frequently formed of only one layer of cells, and consequently stomata are wanting; the formation of the prothallium also somewhat resembles the Mosses. Sori marginal, on the extremities of the vascular bundles, and surrounded by a cupular indusium. The sporangia are sessile, with equatorial annulus. Hymenophyllum (H. tunbridgense, European). Trichomanes (T. speciosum, European). Species about 200, which live especially on rocks and trees in damp and shady tropical forests. Some have no roots.

Order 3. =Cyatheaceæ.= Annulus complete and oblique. To this order belong, principally, the tree-like Ferns with palm-like habit. The number of species is about 200, they are all tropical and form forests in some regions of Australia. Cibotium and Dicksonia have marginal sori, with cupular, basal indusium. (The stem of D. antarctica is covered with aerial roots.) Alsophila (without indusium); Cyathea with cupular, inferior indusium (Fig. 212 E).

Order 4. =Gleicheniaceæ.= Sporangia with equatorial annulus, and longitudinal dehiscence, most frequently groups of 3–4 in sori without indusium (Fig. 213). Gleichenia: the apical growth of the leaves continues for a long time.

Order 5. =Schizæaceæ.= Annulus apical. To this order belongs Aneimia, which is so commonly cultivated in conservatories. The two lowest pinnæ are metamorphosed, having no leaf parenchyma and being covered with sporangia. Schizæa. Mohria. Lygodium, a climber, whose leaves have unlimited growth and attain a length of several metres. About 70 species. Tropical.

Order 6. =Osmundaceæ.= The sporangia have at the apex a lateral group of strongly thickened cells, which gradually pass over into the ordinary cells. The sporangia open by a longitudinal cleft. Indusium wanting. Osmunda bears the sporangia upon peculiar, branched pinnæ, without parenchyma (the uppermost in the leaf). O. regalis (Royal-Fern): European.

Sub-Class 2. =Hydropterideæ= (formerly Rhizocarpeæ), =Water Ferns=.

The following further characteristics must be added to those given on page 205:--

=Sexual generation.= The MICROSPORES produce an extremely rudimentary prothallium, formed of only a single cell, and having also a very much reduced bicellular antheridium with a small number of spermatozoid mother-cells in each cell (in Salvinia 4, in Marsilia and Pilularia 16). In Salvinia the microspores remain embedded in a hard mucilaginous mass (at first frothy) which fills up the cavity of the sporangium. The prothallium must therefore grow out through this slime and also through the wall of the sporangium (Fig. 214), and it thus terminates in a relatively long cell.

In Marsilia the microspores are set free from the microsporangium, and the prothallia, with the antheridia, remain in them until the spermatozoids are liberated. The latter are spirally-twisted threads.

The MACROSPORES, on germination, give rise to a very reduced prothallium, which in Salvinia bears 3 archegonia; but, if these are not fertilised, the prothallium may continue to grow and become a fairly large, green body with several archegonia (Fig. 215 A, B). In Marsilia the prothallium is still more reduced, it is enclosed in the macrospore, and only bears one archegonium. The archegonia are similar in structure to those of the Ferns, but are smaller, and sunk more deeply in the tissue of the prothallium.

=The asexual generation= is developed from the fertilised egg-cell. It is a dorsiventral, horizontal shoot. In Salvinia it bears at first a shield-like leaf, the scutiform leaf (Fig. 215 C, a), which is succeeded by the ordinary foliage-leaves. The young plants of Marsilia, likewise, have less perfect leaves in the very early stage.

The formation of the sporangium is the same as in the Leptosporangiate Ferns. (The 16 spore-mother-cells originate from one central, tetrahedric archesporium.)

The Hydropterideæ are divided into 2 orders, the chief differences between them being found in the asexual generation.

Order 1. =Salviniaceæ.= This order more nearly approaches the true Ferns, especially so on account of the form of the indusium. Only one species is found in Europe, Salvinia natans (Fig. 217). This is a small, floating, annual, aquatic plant, entirely destitute of roots. The dorsiventral, horizontal stem bears two kinds of leaves, which are arranged in whorls of three. Two of these which turn upwards are oval, entire, “aerial foliage-leaves” (Fig. 217 B, b^2-b^3); the third, the “water-leaf” (b^1) is submerged and divided into a number of hair-like segments, similar to the submerged leaves in many aquatic plants, for instance, Water-buttercup (see also Fig. 215 C). The whorls of leaves alternate with each other; there are thus 4 rows of dorsally-placed aerial leaves, and two rows of ventrally-placed submerged leaves. The sporangia are situated in sori, each sorus being borne on a small column (receptacle or placenta) and enveloped by a cupular, but entirely closed indusium (Fig. 218). The sori are situated on the submerged leaves (Fig. 217 B, s-s) and are unisexual, i.e. each sorus contains microsporangia only, or macrosporangia.

Azolla belongs to this order. It is a very small, floating, tropical water-plant (America and East India), with horizontal, root-bearing stem. The stem branches profusely by lateral buds, and bears the two rows of leaves on its dorsal side, the roots on the ventral side. Each leaf is bifid, and divided into an upper dorsal, and a lower ventral portion. The upper segments float on the surface of the water and are arranged like tiles on a roof, each one overlapping its neighbour. In each floating segment a large cavity is found, in which Anabæna is always present. The lower segments are submerged.

Order 2. =Marsiliaceæ.= The characteristic feature of this order, and one not possessed by other Fern-like plants, is that the sori (2–many) are enveloped in leaf-segments which close round them and form a “sporocarp,” just in the same manner as the carpels, in the Angiospermous Flowering-plants, close round the ovules and form ovaries. The sori contain both micro-and macrosporangia. When the spores are ripe, the sporocarp opens in order to disperse the spores (Fig. 220).

The two genera (with 57 species, Temperate, Tropics) are land-and marsh-plants, whose dorsiventral, creeping stem bears roots on the under surface, and the leaves in two rows on the upper side (Figs. 219, 221). The leaves of Marsilia are compound, and divided into four small leaflets springing from the apex of the petiole (Fig. 219), and resemble the leaves of Oxalis. In the bud the leaves are circinate (Fig. 219 b), and at night they exhibit the well-known sleep-movements. The sporocarps are borne on the petioles of the fertile leaves, near their bases (Fig. 219 f); they are oblong and resemble small beans, the outer cells being hard and sclerenchymatous, while the inner ones are divided into a number of loculi arranged in two rows. On germination, water is absorbed, the two sides separate slightly, as valves (Fig. 220 A), and a long vermiform mass of gelatinous, parenchymatous cells (Fig. 220), swollen by the water, emerges, bearing a large number of sori arranged pinnately. Each sorus (sr) is covered by a thin indusium. (The thin covering may be considered an indusium physiologically, though not morphologically).

Marsilia quadrifolia, in Europe. Many species are found in Australia. The nutritious sporocarps of M. salvatrix were the means of saving the Burke expedition in the interior of Australia, and hence this species has earned its specific name.

Pilularia has linear leaves, without lamina. The sporocarps are spheroid (Fig. 221), brown and hard, and situated near the base of the leaves. They are 2–4 chambered and open by a corresponding number of valves.

Class 2. =Equisetinæ (Horsetails.)=

The characteristics of this class have been described on page 204.

It is divided into two sub-classes:--

1. THE ISOSPOROUS EQUISETINÆ. To this sub-class belong, with certainty, only the EQUISETACEÆ now existent, which are represented by only one genus, Equisetum.

2. THE HETEROSPOROUS EQUISETINÆ. Forms which are now extinct.

Sub-Class 1. =Isosporous Equisetinæ.=

Order. =Equisetaceæ (Horsetails).=

=The sexual generation.= The prothallium is green and leaf-like, as in the majority of Ferns, but irregularly branched and curled. It is often unisexual. The male prothallia bear antheridia only, and are smaller and less branched (Fig. 222 A) than the female; the latter may attain a diameter of ½ an inch, and bear archegonia only (Fig. 222 B). The antheridia and the archegonia resemble those of the Ferns, but the spermatozoids (Fig. 223) are larger and less twisted. On the last curve is situated a more or less elongated appendage of cytoplasm (Fig. 223 c).

=The asexual generation.= The embryo is similar to that of the Ferns. The fully developed Equisetum is a perennial herb, with widely creeping (in some species tuberous) rhizome, from which extend erect, aerial, most frequently annual shoots.

The vegetative aerial STEMS are divided into a number of internodes by the whorls of leaves (Fig. 224). The internodes are hollow, the cavities being separated from each other by the transverse partitions of the solid nodes. The lower portion of the internode, which is encased by the leaves, has much thinner and softer cell-walls, so that the stem is easily separated into segments just above the nodes. Each internode has a large number of ridges and furrows, and bears at its apex a whorl of leaves whose number and position correspond to the ridges of the internode. As in the case of other verticillate plants, the whorls are placed alternately, one above the other; the same arrangement is also found in the ridges on two successive internodes. In addition to the large air-cavity in the centre of each internode (the central cavity), a whorl of tubular air-passages is found in the cortex of the stems, opposite the furrows (vallecular canals). There is also a similar air-passage (carinal canals) in each of the vascular bundles, which are placed in a ring, one opposite each ridge, and therefore alternating with the vallecular canals. The vascular bundles are collateral as in the majority of Flowering-plants, but poorly developed. The xylem of each bundle consists of two groups of annular or spiral vessels, close to the outer border of the carinal canal, and two groups of scalariform tracheides, each placed on a radius passing through a group of spiral vessels. The phloëm is placed between these four groups, each of which has only a few vessels. The stiffness of the stems is mainly due to the large amount of silica in the cell-walls of the epidermis, and to the sclerenchymatous cells of the ridges.

All LEAVES are situated in whorls. The VEGETATIVE are simple, undivided, 1-nerved, and are united into toothed sheaths (Fig. 224 a, b). The branching of the stems in some species (E. arvense) is very abundant. The branches break through the base of the leaf-sheaths (Fig. 224 b), and generally alternate with the teeth (leaves).

The FERTILE LEAVES (sporophylls) are different from the barren ones. They are free, shield-like, each one having a short stalk bearing usually an hexagonal plate (Fig. 224 d), and closely compressed into an ear or cone (Fig. 224 a, c). The Equisetums thus present an advance in development distinctly beyond that of the Ferns, which is further emphasized by the circumstance that a transition from the sheath-leaves to the fertile-leaves is found in the involucre or annulus, a “collar” of specially modified leaves situated at the base of the cone (Fig. 224 a and c). The cone may be considered as a very rudimentary flower, and the annulus may be regarded as a very early stage in the formation of a flower (perianth). See page 235.

The SPORANGIA are situated on the underside of the sporophylls, one at each angle; they are sac-like, and open inwardly by a longitudinal cleft (Fig. 224 d). An annulus is wanting; but in the wall of the sporangium, as in the pollen-sacs of the Flowering-plants, a layer of cells, with annular or spiral thickenings, is developed, which assists in the dehiscence of the sporangium.

The SPORES are green; the walls composed of four distinct layers, of which the outer is gradually separated, except at one point, and becomes split into four long bands (elaters) (Fig. 225). The elaters are extremely hygroscopic, coiling round the spore when moistened, and expanding as soon as dry, presenting a most lively object under the microscope when breathed upon and allowed to dry. The second layer, when germination commences, becomes detached from the inner wall, which is formed of the exospore and endospore.

The order has become much reduced, and at the present time includes only one genus, Equisetum, with about twenty-five species, which are distributed over the entire globe, particularly in damp situations. In SOME SPECIES the barren shoots are green and very much branched, but the fertile ones are unbranched, pale brown, and possess no chlorophyll (E. arvense, Field-Horsetail, Fig. 224, and E. maximum). IN OTHERS the fertile and barren shoots are alike green, and either both unbranched (E. hiemale), or branched (E. palustre, E. limosum, etc). The fertile shoots of E. silvaticum, up to maturity, resemble those without chylorophyll of E. arvense, but after that period they produce green branches, and thus resemble the barren ones.

EXTINCT ISOSPOROUS EQUISETINÆ. In addition to several true species of fossilized Equisetums, the order of the CALAMITES, which no doubt is closely allied to the Equisetinæ, is also found in the fossil state. These were gigantic forms, attaining about twenty times the size of those of the present day, and stems of nearly 10–12 metres in height are known. They reached the culminating point of their development in the Carboniferous period, and died out towards the close of the Palæozoic. The stems had hollow internodes and alternating grooves, similar to their relatives of the present day. The leaves must either have been absent or very perishable, since they have not been identified with certainty. If the determinations of certain remains of cones which of late have been discovered are correct, they were heterosporous and had two kinds of sporangia as in the following sub-class. A cambium formation and an increase in thickness has been found in the stems.

Their USES are very limited. A few species, such as E. hiemale are used for polishing on account of the hard siliceous cell-walls of the epidermis, found in all species of Equisetum.

Sub-Class 2. =Heterosporous Equisetinæ.=

The two orders which come under this head are united by the characteristics, that the verticillate leaves are not united into sheaths (Fig. 226), and that between each whorl of fertile leaves there is also a whorl of barren ones. The fertile whorls in ANNULARIÆ are situated about midway between the barren ones (Fig. 227), but in ASTEROPHYLLITEÆ they occur immediately above a barren whorl (Fig. 228) and contain only half as many members as the latter. The lower whorls bear macrosporangia with one macrospore, the upper, microsporangia with many microspores.

The ANNULARIÆ were distichous (Fig. 226), and presumably floating plants. The ASTEROPHYLLITEÆ had verticellate branches. These also died out after the Carboniferous period, at the close of the Palæozoic.

Class 3. =Lycopodinæ= (=Club-Mosses=).

The characteristics of this class have been given on page 205. It consists of two sub-classes, one embracing isosporous, the other heterosporous forms.

Sub-Class 1. =Lycopodieæ= (ISOSPOROUS Lycopodinæ).

One kind of spore. Prothallium large, partly green. Leaves without ligule.

Order 1. =Lycopodiaceæ.= The PROTHALLIUM is only known in a few species at present, but in these it is more or less tubercular, and bears both antheridia and archegonia.

In L. annotinum the prothallium is a relatively large mass of cells, without chlorophyll, and subterranean, in which the antheridia and archegonia are embedded (Fig. 229). In the widely distributed tropical species, L. cernuum, and in L. inundatum, it is a small tubercular body which has a subterranean portion, with either little or no chlorophyll; and an aerial green portion. The prothallia of L. phlegmaria and others live saprophytically in the crevices of the bark of trees; they are partly filamentous, branched, and possess no chlorophyll.

The =asexual generation=. PERENNIAL PLANTS. The stem branches monopodially (often apparently dichotomously), and is thickly covered by small, simple, triangular or scale-like leaves. The leaves are spirally arranged in some species (Figs. 229, 230), and in others, whose stem is compressed with unequal sides, opposite (Fig. 231). The roots of Lycopodium are dichotomously branched.

The SPORANGIA in Lycopodium are situated singly at the base of the leaves, almost in their axils; they are reniform, unilocular and open like a mussel-shell by two valves (Fig. 230 h). The sporangia are developed from a group of surface cells. The archesporium is formed from one hypodermal cell (or perhaps a cell-row).

The fertile leaves are collected upon definite regions of the stem. They are either similar to the barren ones, and then the fertile portions of the stem pass gradually, without any break, into the barren portion (L. selago); or they differ from the barren leaves, and are then collected into special apical cones (Fig. 230 a). The SPORES are tetrahedral or bilateral (Fig. 232).

About 100 species, chiefly tropical.

Five species of Lycopodium are found in Great Britain. L. clavatum and L. selago are common in mountainous districts. L. annotinum is common in the Highlands of Scotland. The other genus of the order is Phylloglossum, with one species, P. drummondi (Australia, Tasmania, and New Zealand), a small plant only a few centimetres high, with two tubers, and about eleven linear leaves at the base of the stem which is terminated by a cone of sporophylls.--FOSSIL Lycopodiaceæ in the Carboniferous period.

OFFICINAL: “Lycopodium,” the spores of L. clavatum.

Family 2. =Psilotaceæ=. The sporangia are placed on the apex of short, two-leaved stems, as 2–3, seldom four, small capsules. Small herbs, with angular stems; leaves small, simple, and one nerved. Only four species.--Psilotum (Madagascar, Moluccas, Sandwich Islands, etc.) is destitute of roots, their place being supplied by special underground stems which bear a few modified leaves, very much reduced, especially when buried deeply in the soil. Three species.--Tmesipteris (Australia), one species.

Sub-Class 2. =Selaginelleæ= (HETEROSPOROUS Lycopodinæ).

Micro-and macrospores. The prothallia are very much reduced, especially the male; the female does not leave the spore. The leaves are ligulate.

=The sexual generation.= In the ~MICROSPORES~ are formed: (1) a very small “vegetative” cell, representing the vegetative part of the prothallium (f in Fig. 233 A, B), and (2) a cell many times larger and which divides into a number (4–8) of primordial cells, each of which divides into four spermatozoid-mother-cells, though all of these may not develope spermatozoids. On germination, when the spore-wall is ruptured, the spermatozoids and spermatozoid-mother-cells are ejected into the water.

The ~SPERMATOZOIDS~ in Selaginella are elongated and club-shaped, with two cilia (Fig. 234); but in Isoëtes lacustris they are spirally-twisted threads which differ from all other spermatozoids by having a bunch of cilia at each end; the other species of Isoëtes have cilia only at the anterior end.

The MACROSPORES. Shortly after the macrospores have been set free, or in Selaginella, while still enclosed in the sporangium of the mother-plant, they germinate and soon become filled with the cellular tissue of the prothallium, and even in Selaginella the archegonium begins to be formed before the rupture of the spore-cell-wall has commenced (Fig. 235 A).

The ARCHEGONIA are constructed on the same plan as those of the other Archegoniatæ, but are quite embedded in the prothallium (Figs. 235 æ, 236).

=The asexual generation= varies very much in the different orders.

Order 1. =Isoëtaceæ (Quill-worts).= The only known genus, Isoëtes (Quill-wort), has an extremely short, tuberous, unbranched stem with very short internodes (Fig. 237). The STEM is remarkable as being the only one among the Vascular Cryptogams which increases in thickness (see page 202). The meristematic cells are situated round the axial cylinder, and form, especially, parenchymatous tissue in two or three directions, giving rise to 2–3 grooves in which the dichotomously-branched ROOTS are produced. The LEAVES are arranged spirally in a close rosette. They are awl-shaped and have at the base a semi-amplexicaul sheath, with a groove (fovea), in which a sporangium is situated (Fig. 238). The ligule is a foliar outgrowth from the upper edge of the groove.--The MACROSPORANGIA (each with a number of macrospores), are situated on the outer leaves, the MICROSPORANGIA (Fig. 238), on the inner ones. Between each cycle of fertile leaves there are a number of imperfect or barren ones as in the case of the female plant of Cycas. The spores are liberated by the decay of the sporangium. The two kinds of sporangia develope at the commencement in the same way. The archesporium is, at first, a hypodermal layer of cells which grow out in the direction perpendicular to the surface of the leaf, and divide by a number of walls parallel to this direction, forming a sporogenous mass of cells. Some of the cell-rows of this sporogenous mass lose their rich protoplasmic contents, and are arrested in their growth; thus incomplete divisional walls of sterile cells, “trabeculæ” arise in the sporangium, dividing it into a number of compartments one above the other (Fig. 238 t). (The trabeculæ, according to Goebel, play the same part as the nutritive cells of the sporangium of Riella; the tapetal cells, as in the Ferns, are in a great measure dissolved at a later period.) The sporogenous cell-rows, in the microsporangia, give rise to a large number of spore-mother-cells, but in the macrosporangia only one spore-mother-cell, with tapetum, is developed from each fertile archesporial cell.

The two native species, and several others, are aquatic plants, the remaining species are land plants, or are amphibious. About 50 species. In temperate and tropical regions.--FOSSIL species in the Tertiary period.

Order 2. =Selaginellaceæ.= This order contains only one genus, Selaginella. The STEM, in the majority of species, is dorsiventral, long and slender, and apparently branches dichotomously, but in reality monopodially, with well developed lateral shoots. The LEAVES are small, round, or ovate, in the majority of species arranged in whorls of two leaves each; these whorls, however, are not decussate, but are considerably inclined towards each other, an arrangement by which four rows of leaves are produced, each whorl having one large and one small leaf. The two leaves in each whorl are of unequal size, the smaller one being placed on the upper surface and the larger on the lower surface of the stem (Fig. 240). Some species have spirally-arranged leaves, more resembling the arrangement in the Lycopodiums.

The ~FERTILE LEAVES~ most frequently differ from the barren ones, and are collected into spike-like cones (a kind of flower; Fig. 239). Micro-and macrosporangia are found in the same cone (Fig. 239). Each sporangium arises from a group of superficial cells of the stem, directly over the leaf on which it will be situated later on. Each sporangium has a hypodermal, unicellular archesporium, and contains a layer of tapetal cells; these are dissolved later, when the spores are ripe, and not before as in the Ferns. In the very early stages of their development, the micro-and macrosporangia are precisely similar, and the differences between them arise later on. In the microsporangium all the spore-mother-cells divide, and each forms four tetrahedrically-arranged microspores (Fig. 204); but in the macrosporangium only four macrospores are formed, by the division of a single mother-cell, while the remaining spore-mother-cells are aborted. It is rarely that the macrosporangia contain 2 or 8 macrospores.

For the ~GERMINATION OF THE SPORES~, see pages 228, 229. The prothallium arises in the macrospore (f-f, in Fig. 235 A), probably by division of the meniscus-shaped protoplasmic mass, which is marked off at the apex of the spore; primordial cells are thus formed which later on are surrounded by a cell-wall. In six to seven weeks after sowing, the spore-wall is ruptured by the growing prothallium, which already has developed archegonia (Fig. 235 œ-œ). The prothallium so formed does not occupy the entire cavity of the spore, but four to five weeks after sowing, the large-celled parenchyma is developed in the lower portion of the spore by free cell-formation; this has been termed by Pfeffer, “endosperm,” since it is similar to the endosperm of Flowering-plants. Goebel, however, has termed it “secondary prothallium,” as the homology with the endosperm of the Angiosperms is very doubtful.

The ~FERTILISED OOSPHERE~ divides into an upper (hypobasal) and a lower (epibasal) cell; from the latter alone the embryo is developed with its root, stem, foot, and two cotyledons, and the former gives rise to an organ which appears in this instance for the first time, but which occurs in all Flowering-plants, viz. the suspensor. This forces the embryo down into the “endosperm,” which is entirely or partially absorbed by the embryo. In the case of the Flowering-plants the embryo is developed with its longitudinal axis in the elongation of the suspensor, but in Selaginella the embryo is situated transversely to it.

Selaginella (300–400 species), is essentially tropical, only one species living in the North (S. spinulosa), but others grow in Central and South Europe.

Order 3. =Lepidodendraceæ= are extinct, tree-like Lycopods, which are found especially in the Lower and Middle Carboniferous. Vegetatively they are most nearly related to Lycopodium, but the stem attained much larger proportions (about eleven metres in height and one metre in thickness), and had a cambium by which it increased in thickness. It was regularly dichotomous, and closely studded with spirally-placed leaves, which left behind them peculiar rhombic scars. The large cones resemble Pine-cones, and bore sporangia much larger than any which are now produced (the male ones as much as 2 cm.’s in length). The macrosporangia were situated at the base, and the microsporangia at the apex.

Order 4. =Sigillariaceæ.= These are, presumably, another group of extinct tree-like Lycopods (especially in the Middle Carboniferous). The name has been derived from the seal-like scars, which the fallen leaves have left behind in longitudinal rows on the grooved stem. The rhizomes of these plants were formerly termed Stigmaria, and placed in a separate genus.

Order 5. =Sphenophyllaceæ= form an entirely extinct group. They do not definitely belong to any of the three large classes of Vascular Cryptogams, but it is perhaps best to place them in juxtaposition to these. They were herbaceous plants with verticillate, wedge-shaped leaves, with nerves branching dichotomously into equally strong branches. Micro-and macrosporangia were formed in the same cone; and were situated in the axils of the leaves, as in the Lycopods.

The Transition from the Cryptogams to the Phanerogams.

All the plants considered in the preceding chapters are included in the term CRYPTOGAMS; all in the following chapters under the head of PHANEROGAMS (see page 3). Hofmeister’s pioneer works (1851, Vergleichende Untersuchungen der höheren Kryptogamen, etc.) and the numerous researches published later by other investigators, have closed the gap which was formerly thought to exist between these plants; so that we now, in the series: Bryophyta--Pteridophyta--Gymnospermæ--Angiospermæ see the expression of a single line of development in accordance with a definite plan. The forms through which this gradual development has taken place have in course of time, however, to a great extent died out, and only single links of the chain connecting the lowest to the highest still remain.

THE ALTERNATION OF GENERATIONS, which we found indicated in certain Thallophytes, can be proved with the greatest clearness in all the higher Cryptogams, from the Mosses upwards; it is also found in the Phanerogams, but not in such a pronounced degree, because one of the generations is so far reduced that it has almost given up its independence. For the sake of greater clearness, we will begin with the comparison of the sporophyte, asexual (second) generation.

=The asexual (2nd) generation of the Cormophytes.=

The asexual generation which follows from the further development of the fertilised oosphere, is, in the Mosses, only the sporogonium (according to one theory it is perhaps homologous with a spore-bearing leaf, situated upon a short stem, see p. 187); in Filicinæ, Equisetinæ, and Lycopodinæ, on the other hand, it is a highly developed plant differentiated into stem, leaf, and true root, and bearing the sporangia on its leaves. The ~MODIFICATION OF THE SHOOT~ is very slight in Filicinæ. The first leaves of the embryo are very simple in form (Fig. 205), but after a certain age all the leaves which arise are essentially alike. The fertile leaves do not differ from the barren ones, and are found associated with them, and their formation does not limit the growth in length of the stem. It is only in a few of the true Ferns, and in the Hydropterideæ, that the fertile leaves differ considerably from the barren ones. A division of labour in which certain leaves are set apart for nutrition, and others for reproduction, is found more pronouncedly in the Equisetinæ and Lycopodinæ, for in these groups, with a few exceptions, the fertile and barren leaves are very dissimilar; the former are collected in special ear-like cones, which terminate the further growth of the short stems on which they are borne. In connection with the cone, leaves are sometimes developed which form a transition from the barren to the fertile ones (the “annulus” in Equisetaceæ), and in these cases the first indication of a flower with perianth or floral-leaves is to be traced. Among the Cryptogams the highest division of labour is found in Selaginella and Isoëtes, which have the two kinds of sporangia borne on different leaves. The division of labour (modification) is, however, still more pronounced in the Phanerogams: the leaves which bear the microsporangia (“pollen-sacs”) have quite different forms from those which bear macrosporangia (the “nucellus” in the ovule), the former are termed stamens, the latter carpels; in certain instances, too, there is even a contrast between the “male plants” and the “female plants.” Moreover, a division of labour, in a much greater degree, takes place in the leaves which do not directly take part in reproduction, and it is thus possible in many plants to draw a sharp line not only between stamens and carpels, but also between four or five distinct kinds of leaves, which differ in form, structure, and corresponding functions, and which appear in regular sequence on the shoot: namely, between “scale-leaves” and “foliage-leaves,”[21] both of which occur in the Cryptogams, and the “floral-leaves,” including the bracts and leaves of the “perianth,” which latter often differ from each other in form and colour, and are then separated into sepals and petals. The leaves--stamens and carpels--which bear the sporangia are termed sporophylls, and the shoot, or extremity of a shoot, whose leaves are modified into sporophylls, is terminated in its further growth by their production, and is known as a flower. The flower which is most completely furnished has calyx, corolla, stamens, and carpels arranged in this order. If the only sporophylls present are stamens, then it is said to be a male (staminate) flower, and if only carpels, then a female (pistillate) flower, and in both these cases the flowers are unisexual, or diclinous. If stamens and carpels are both present in the same flower, it is termed hermaphrodite. Diclinous plants in which the female flowers are situated on one plant, and the male flowers on another, are termed diœcious; and those in which the same plant bears the two kinds of flowers are termed monœcious. When the male, female, and hermaphrodite flowers are found in the same species, the plant is said to be polygamous.

=The sporangia-bearing leaves--Sporophylls.= In the Mosses the asexual generation is only represented by the sporogonium, and if the theory is correct which considers the sporogonium to be an embryo consisting of a rudimentary stem and terminal leaf, then the spores are produced on the leaves in these plants. The sporangia in the Filicinæ are situated in groups (sori) on the back or on the edge of the leaves. The number of sporangia in the sorus diminishes very greatly in the Marattiaceæ and Gleicheniaceæ (three to four in the latter, Fig. 213). In the Equisetinæ the sporangia are situated in a small number on the underside of shield-like leaves, and in Lycopodinæ, singly, in the axils of the fertile leaves, which are alike and bear either micro- or macrosporangia. In the Phanerogams there is a great difference between the stamens and carpels.

=Stamens.= In the lowest Phanerogams (Cycadeæ) there are many indications of relationship to the Ferns. The stamens are flat and broad, and have on the back many pollen-sacs (microsporangia) arranged in small groups (true sori), which even have a small “placenta,” similar to the one possessed by the Ferns, and open towards the inside by a longitudinal cleft (Fig. 241, compare Fig. 213). A section of the Coniferæ agree more closely with the Equisetaceæ, in having a few (three to eight) pollen-sacs arranged on the underside of more or less shield-like leaves (Figs. 242, 243, compare with Fig. 224 a, c, d). In the Abietaceæ the number of sporangia is diminished to two, which are placed also on the lower side (Fig. 267) of a stamen. The number of pollen-sacs (microsporangia) in the Angiosperms is nearly always four to each stamen; they are longitudinal projections which are placed in pairs on each side of the central line of the stamen, two on the edge, and the other two generally on the side which is turned inwards; the pollen-sacs generally dehisce longitudinally (quadrilocular anthers, Fig. 244). A few, for instance Orchidaceæ and Asclepiadaceæ, have only two pollen-sacs (bilocular anthers); and in others, such as Solanum and the Ericaceæ, they open by pores; in Lauraceæ and Berberidaceæ, by valves. The part of the stamen which bears the pollen-sacs is termed the anther. Most frequently this is supported by a stalk known as the filament.

=Carpels.= The simplest forms of carpels are found in Cycas. In this genus both the foliage and fertile leaves are pinnate, and hence present great similarity; the ovules (macrosporangia) are situated on the margin of the central portion, just as the sporangia are placed on the edge of the fertile leaf of Ophioglossum (Fig. 245, compare with Fig. 209). The carpels of the other Cycadeæ present greater divergence from the foliage-leaves, being peltate, for instance, in Zamia and Ceratozamia (Fig. 246). The ovules in the Coniferæ are situated on the upper side and near the base of the ovuliferous scales, almost in the same position as the sporangia in the Lycopodinæ (Figs. 269, 272, 273 H, compare Figs. 230, 239). In Taxus the uninclosed ovule is placed on the apex of a shoot (Fig. 264). In all these plants the ovules are not enclosed by the carpels, that is, they are not enclosed in chambers formed by the turning in of the walls of the carpel, and hence the name Gymnospermæ is given to them. In the higher Flowering-plants, the Angiospermæ, the ovules are distinctly situated on the edge, the upper surface, or base of the carpel; but the carpel closes round the ovules which are therefore enclosed in a chamber--the ovary. In a few cases, for example in the Polygonaceæ, an ovule is situated apparently on the apex of the stem itself, as in the Yew; in other cases, as in the Primulaceæ, many ovules are apparently developed on the apex of the stem, which seems to have been specially adapted as a placenta, but it is also possible and correct in these cases to suppose that the ovules are in reality developed on the carpels.[22] A single fully-developed carpel or a collection of carpels joined together is termed the pistil. The extremity of the carpel, which is specially developed to catch the pollen-grains and form a suitable nidus on which they may germinate, is called the stigma. The united edges of a carpel which bear the ovules are termed the ventral suture. The back of the carpel forms the dorsal suture. The Marsiliaceæ take a position among the Hydropterideæ analogous to that occupied by the Angiosperms; the sporangia are in a corresponding manner enveloped in a closed leaf.

The collection of stamens in a flower is termed the andrœcium, and all the carpels, whether individually free or united into one pistil, the gynœceum.

The =Sporangia=. The asexual generation of the Mosses is the sporogonium, in which the spores arise in tetrads from the mother-cells. The sporangia in the Filicinæ take their origin either from a single cell (Leptosporangiatæ) or, what probably may be regarded as an older stand-point, from a group of cells (Eusporangiatæ). In both cases there may be distinguished in a mature sporangium three tissues, which have different significance (Fig. 204): (1) an external layer, the sporangium-wall, most frequently composed of one layer of cells made up of cells of dissimilar structure, so that on desiccation the wall is ruptured and the sporangium opens in a definite manner; (2) an internal group of cells, consisting of the spore-mother-cells, developed from an archesporium, and which by division into four gives rise to the spores; (3) a layer of cells lying between the two already mentioned, which is dissolved before maturity. The intermediate cellular layer, which directly surrounds the spore-forming cells, is in form and contents more worthy of note than the others, and is termed the tapetum. The construction of the sporangium in the Equisetinæ and Lycopodinæ is in the main the same.

In the PHANEROGAMS the =Microsporangia= are termed =Pollen-sacs=. They take their origin from a large group of cells, which, in the Angiosperms, lie immediately beneath the epidermal cells of the anther. In the developed, but not yet mature, sporangium (pollen-sac) there are to be found: (as in the Vascular Cryptogams) (1) an internal group of mother-cells which give rise to the pollen-grains (microspores), in this case also formed in tetrads; (2) a group of cells surrounding these, of which the internal ones form a tapetal layer, similar to that in the Vascular Cryptogams; the tapetum and some of the cells surrounding it in this group, become dissolved before maturity; the more external ones, on the other hand, are provided with peculiar thickenings, and form the “fibrous” layer by the aid of which the dehiscence of the anther takes place; (3) an external layer, the epidermis, enclosing all the other layers (Fig. 247).

In some Coniferæ (Cupressus, Thuja, and several species of Juniperus) the microsporangia (pollen-sacs), which are situated on the under side of the stamen, are covered by a thin structure which seems to be a continuation of the lamina and which is supposed to be homologous with the indusium of the Ferns.

=The Ovule= in the Phanerogams arises most frequently on a projecting portion of the carpel, termed the placenta. The ovules (compare the sporangium of the Eusporangiatæ and especially the pollen-sac) take their origin from a group of cells which lies beneath the epidermis (Fig. 248 A, B). First of all a small papilla is formed, which is later on provided with a vascular bundle and becomes the funicle; this probably has the same value as the projections (“placenta”) on which the sori in the Ferns are attached. Only one =macrosporangium= (nucellus; Fig. 248 nc) is developed at the apex of the funicle. This arises by a process of cell-division exactly corresponding to that by which the pollen-sacs are formed (Fig. 248 C-E), with this difference only, that while a great many cells may be distinguished in each pollen-sac, which forms pollen-grains by tetrad-division, only a few are found in the ovule, and all these moreover are suppressed, with one single exception which developes into the =macrospore= (=embryo-sac=) without undergoing a division into tetrads. The wall of the embryo-sac, in the Gymnosperms, may be thick and divided into two layers and partly cuticularized, as in the spores of the Cryptogams which are to be set free. In the Angiosperms, on the other hand, the wall is extremely thin.

The pollen-sac thus stands in the same relation to the nucellus as the microsporangium does to the macrosporangium: in the pollen-sacs and microsporangia a number of spores arise by the tetrad-division of several mother-cells; in the nucellus and macrosporangium, a reduction of the cells already formed takes place to such an extent that the number of macrospores becomes one (Salvinia, Marsilia, Phanerogams) or four (Selaginella), or rarely a large number as in Isoëtes.

In the Ferns, as stated on page 210, etc., indusia covering the sori very often occur. Horsetails and Club-Mosses have no indusium; but in all Phanerogams cupular or sac-like structures (integuments) are found which envelop the nucellus. These develope from the upper end of the funicle (ii and ie, in Fig. 248; y and i, in Fig. 249) and enclose the nucellus on all sides as a sac, leaving only a small channel at the apex of the nucellus--the micropyle--(Fig. 249) through which the pollen-tube proceeds to the embryo-sac. The ovules of the Gymnosperms have only one integument (Figs. 251, 264, 269, 274) and the same is the case with the majority of the Sympetalæ and a few Choripetalæ; but the Monocotyledons and most of the Choripetalæ have two integuments (Fig. 249).

In shape the integuments resemble very closely the cupular indusium of the Hymenophyllaceæ, certain Cyatheaceæ (Fig. 212 E), and Salvinia (Fig. 218); that they are really homologous with these is probable, but is not proven. Some authorities regard them as structures found only in the Phanerogams.

The ovule is thus a “monangic” (i.e. reduced to 1 sporangium, the nucellus) sorus, situated on a funicle, and enclosed by one or two cupular indusia, the integuments. Some of the ovules are erect (orthotropous), others curved (campylotropous), the majority reversed (anatropous) (Fig. 249).

[Goebel (1884 and earlier) with Strasburger considered the entire ovule of the Phanerogams as homologous with the macrosporangium, the integuments however as new structures in contradistinction to the Ferns: the funicle then corresponds to the stalk of the sporangium. The integuments of the ovule (according to Goebel, 1882) differ from the indusium of the Fern-like plants in being developed from the basal portion of the nucellus and are not, as in the Ferns and Isoëtes, a portion (outgrowth) of the leaf which bears the sporangia (K).]

The nucellus is the only macrosporangium which never opens; the macrospore remains enclosed in it, and the macrosporangium remains attached to the mother-plant. It is therefore essential that the method of fertilisation which is employed should be very different from that of the Cryptogams. The pollen-grains must be transferred to the ovule, and retained either by a drop of mucilage at the micropyle (Gymnosperms) or by the stigma on the carpels (Angiosperms). Fertilisation by spermatozoids, which are freely motile in water, is abandoned in the Phanerogams.

Many other modifications, unknown in plants of more simple structure, take place, for instance, in the shoots which bear the fertile leaves; especially in the form of the stem or thalamus (hypogynous, perigynous, epigynous); in the development of the perianth which stands in intimate connection with the special means employed to effect fertilisation; with respect to the different grades of union found in the leaves; in the union of the flowers into aggregations of a higher order (inflorescences), and at the same time the production of “floral-leaves” (page 235).

=The sexual generation. The Fertilisation.=

The sexual generation in the Mosses is relatively well developed, because not only the protonema, but all the other vegetative parts of the Moss-plant, in addition to the archegonia and antheridia, belong to it. In the groups which follow, a gradual but increasing reduction of the sexual generation takes place, and at the same time an indication of sex is found in the prothallia, which finds expression in the forms of the spores themselves. In the majority of cases among the isosporous Vascular Cryptogams, the sexual generation--prothallium--is a green, leafy expansion which can sustain itself by the assimilation of carbonic acid, and by the absorption of nutriment from the soil by means of root-hairs. In some plants (Ophioglossaceæ, Lycopodium annotinum) the prothallium is a subterranean, pale, tubercular body, but in these instances it is relatively large. In the heterosporous Vascular Cryptogams and in the Phanerogams, the prothallium is much more reduced, both as regards its size, and also with respect to the number and structure of the antheridia and archegonia.

1. =The Microspores.= The PROTHALLIUM in all Vascular Cryptogams which have unequal spores, consists of a single, vegetative (barren) cell, which plays a very unimportant part in the life of the prothallium (Fig. 233 A). In Salvinia it is somewhat elongated and tubular, because it must break through the sporangium (Fig. 214); but in other cases it is very small and lenticular. In all these plants only one antheridium is formed. In Salvinia it consists of 2 cells whose walls are ruptured in order that the spermatozoids may be liberated (Fig. 214 B, C). In Marsilia, Isoëtes, and Selaginella the prothallium does not leave the spore, and consists for the most part of primordial spermatozoid-mother-cells without cell-wall, which on germination are ejected so that the spermatozoids are set free.

In the Phanerogams, the microspores have from olden times been termed pollen-grains.

In the GYMNOSPERMS the prothallium is reduced to 1, 2 or 3 small cells, placed on one side of the mature pollen-grain (at the top in Fig. 250 I, II, and in Fig. 267 N) and which do not play any part in the germination of the pollen-grain. The antheridium is represented by the remaining portions of the interior of the pollen-grain, that is, it consists of a large cell with a nucleus which does not even go so far as the antheridium of Selaginella and become divided into spermatozoid-mother-cells without cell-wall, for even these cells are not formed. The unicellular antheridium grows, on the germination of the pollen-grain, into a tubular body known as the pollen-tube, formed from the inner wall of the pollen-grain (Fig. 250), which works its way down the micropyle to the oosphere. The fertilisation takes place by diosmosis through the cell-wall, and consists here also of the coalescence of the nucleus of the pollen-tube (the sperm-nucleus, male pronucleus) with that of the oosphere.

In the ANGIOSPERMS the reductions proceed still further. The barren cell, which represents the prothallium, was in the last group separated from the antheridium by a true cell-wall, but in the Angiosperms a membrane at most, but no firm cell-wall, is formed. The pollen-grain contains two cells, a vegetative and a free generative cell. Both these pass into the pollen-tube, but the vegetative cell disappears about the time the pollen-tube reaches the ovule; while the generative cell divides into two: one, the sperm-nucleus coalescing with the nucleus of the oosphere, the other being absorbed (Lilium, after Guinard).

The Gymnosperms prove in yet another point that they are more closely related to the Cryptogams than are the Angiosperms. When the pollen-grain begins to germinate the external wall ruptures as in the Cryptogams (Fig. 250), but in the Angiosperms special germ-pores are formed in the cell-wall for the emergence of the pollen-tube.

2. =The Macrospores.= The prothallium in Salvinia and Marsilia is still rather large, green, and capable of the independent assimilation of carbon. It projects more or less from the macrospore and bears (in Marsilia only one, in Salvinia several) archegonia, which however are embedded to a greater degree in the prothallium, and are more reduced than the archegonia of the true Ferns and Horsetails (Figs. 215, 216). The prothallium is still more reduced in Isoëtes and Selaginella; partly because it is smaller and is in a higher degree enclosed in the spore, it also contains less chlorophyll, or is entirely without chlorophyll, and in consequence incapable of independent existence, whilst the number of archegonia is less; and partly because the archegonia are themselves reduced, the cells of the neck are fewer and embedded to the level of the surface of the prothallium without any, or with only a very slight projection (Figs. 235, 236).--Finally, the prothallium with its archegonia begins to develope in Selaginella while the macrospore is still within its sporangium, and before it is set free from the mother-plant. After the spores are set free and germination has commenced, the spore-wall ruptures and the prothallium is exposed.

The GYMNOSPERMS go still further. The macrospore (embryo-sac) germinates and forms internally a cellular tissue, designated in former times by the name of albumen (endosperm), which is homologous with the prothallium. It always remains enclosed in the embryo-sac, and is a parenchymatous mass containing a large supply of nourishment. In the upper part of the endosperm a number of archegonia are developed which are in the main constructed in the same manner as those in the Cryptogams, but are still more reduced, the neck consisting only of 4, 2, or 1 cell (Figs. 251, 252). The ventral canal-cell is also formed, in the majority, as a small portion cut off from the large central cell just beneath the neck; the larger remaining portion becomes the oosphere. When the pollen-tube has passed down to the oosphere (Fig. 253) and fertilisation has been effected, the oospore commences a cell-formation, the final result of which is the formation of an embryo (the asexual generation) which is provided with a thinner, lower end, termed the suspensor. The embryo is forced more or less into the endosperm in which it may rest for a longer or shorter time, and generally is developed to such an extent that it has a distinct primary-root (radicle) and stem (plumule) with one or more embryo-leaves (cotyledons).

When the oosphere has been fertilised its nucleus sinks down to its lower end, and by repeated division into two, forms four cells lying in one plane (Fig. 253, see base of the left archegonium). Three tiers of cells are now formed by transverse division of these four. It is the intermediate one of these which elongates and forms the suspensor, or four suspensors, if they separate from each other, which push the lowermost four cells deep down into the endosperm. It is from these four lower cells that the embryo (or four embryos when the suspensors separate) is developed, but never more than one embryo attains full development. As several archegonia are contained in one and the same ovule, all of which are capable of forming embryos, there is the possibility that several embryos may be developed in a seed (polyembryony), but usually only one embryo attains perfect development.

At the same time that the embryo is being developed, other changes are taking place in the ovule, especially in the integument which becomes the shell of the seed (testa). The endosperm grows, and the embryo-sac supplants the cells of the nucellus. The seed is now formed, and it consists in its most complete development, as in this instance, of three parts:

(1) The testa of the seed, formed by the enveloping integuments, with the remainder of the tissue of the nucellus lying outside the embryo-sac (the macrosporangium).

(2) The endosperm or prothallium.

(3) The embryo.

The reduction in the ANGIOSPERMS is carried to the extreme limit. In the embryo-sac (the macrospore) the nucleus by continued division produces a prothallium consisting of primordial cells (Fig. 254). In the upper end of the embryo-sac (which is nearest the micropyle) are three cells, two of which are termed the “co-operating cells” (synergidæ) and the third is the oosphere. Three others are placed at the opposite end of the embryo-sac and are therefore termed the “antipodal cells.” Finally, a large cell is also formed, which occupies the space between the two groups and whose cell-nucleus, the central definitive nucleus, lies in the centre of the embryo-sac. These primordial cells are the slight remnant of the prothallium. The entire structure of the archegonium, with its neck and canal-cells, has disappeared, and nothing is left but the indispensable oosphere. When the oosphere has been fertilised, and has commenced the cellular divisions which lead to the formation of the embryo (Fig. 255), the synergidæ and antipodal cells are absorbed, and a cell-formation begins by a new process which emanates from the definitive nucleus and by which a parenchymatous cell-tissue, the nutritive-tissue, arises which may perhaps be considered as homologous with the endosperm of the Gymnosperms. The difference is that the nutritive-tissue of the Angiosperms is formed in two parts with an intervening interruption; the primary nutritive-tissue is first formed, and after fertilisation is absorbed, with the exception of one cell, which continues the development and gives rise to the nutritive-tissue proper, which is formed in the first instance of primordial cells, and later on of a cellular tissue; this nutritive-tissue formed in the embryo-sac is termed “endosperm”; in a few instances[23] a tissue which is derived from the nucellus functions as nutritive-tissue, and is termed “perisperm.” In many plants the seeds, when ripe, contain a very rich nutritive-tissue, in addition to the embryo, for the purpose of its nourishment during germination. These are termed albuminous (endospermous) seeds, in distinction to the ex-albuminous, or those in which the nutritive-tissue is stored in the embryo itself, before it is completely developed, and used for its sustenance.

In addition to the changes which fertilisation produces in the ovule itself, it also gives the impetus to a series of changes in the entire shoot which bears the ovule. The perianth, stamens, and style, generally wither, because the part they play is at an end; the wall of the ovary grows and becomes the wall of the fruit (pericarp). The entire gynœcium of a flower, transformed as a consequence of fertilisation, is termed a fruit. It consists of two parts, the pericarp and the seeds, and according to the nature of the pericarp, the fruit is termed a capsule, nut, berry, or drupe.

The chief characteristic of the Phanerogams does not lie in the formation of the flower (although they may quite properly be termed “Flowering-plants”), because Equisetums and Lycopods have reproductive shoots as highly differentiated as those of certain Gymnosperms and other Phanerogams. As regards the SEXUAL GENERATION the characteristics are found:--(1) in its great reduction; (2) in the transmission of the microspore (pollen-grain) to the macrosporangium, and its germination, with the formation of a pollen-tube (antheridium), the protoplasm of which is not differentiated into spermatozoids; (3) in the fact that the macrospore (embryo-sac) never leaves its sporangium (nucellus); and further in the Angiosperms, (4) in the peculiar development of the nutritive-tissue in two parts; and (5) in the great reduction of the archegonium.

As regards the ASEXUAL GENERATION the characteristic feature is that this generation is formed whilst the sporangium is still attached to the mother-plant, and for a long time is nourished by it; and that after the sporangium has become detached from the mother-plant, it spends a longer or shorter resting period as the embryo in the seed (enveloped by the testa), and does not make its appearance until the “germination” of the seed. In addition the shoot which bears sporangia undergoes greater modification than in the case of the Flowerless-plants.

The Phanerogams are separated into two Divisions as follows:--

Division 4. =Gymnospermæ.= The ovules, as well as the seeds, are borne naked on the surface of open carpels, or on the apex of a stem (ovary wanting). The pollen-grains are conveyed by the wind to the ovules, and caught by drops of mucilage, secreted by the micropyle. A “stigma” is wanting. The entire female prothallium (the endosperm), which serves for the nourishment of the embryo, is formed before fertilisation. The archegonia are embedded in the upper part of the prothallium. The pollen-grains are “multicellular,” i.e. there is always in their interior a distinct prothallium, formed by 1–3 cells, and a larger cell which gives rise to the pollen-tube.

Division 5. =Angiospermæ.= The carpels surround the ovules and form an entirely closed chamber (ovary), in which the ovules mature and ripen into seeds. The surface of a portion of the apex of the carpel is transformed into the “stigma,” which, by a sticky fluid and also by hair-structures, is capable of retaining the pollen-grains conveyed to it by the wind, or more frequently by insects. The pollen-tube grows from the stigma, through the “conducting cellular tissue” (style), to the ovules. The pollen-grains contain two cells, a vegetative and a free generative cell. The latter passes into the pollen-tube and there divides into two, one of which is the sperm-nucleus. The female prothallium, which is intended to serve as nutritive-tissue, is formed after fertilisation. Archegonia are wanting.

DIVISION IV.

GYMNOSPERMÆ.

The following characters should be added to those already given on page 2:--

The Gymnosperms comprise only trees or shrubs. The flowers are always unisexual and destitute of perianth (except Gnetaceæ); the female plant of Cycas is the only one which has no flower. The MALE FLOWERS are constructed on the same type as the cones of the Horsetails and Club-Mosses, and are most frequently long shoots (Figs. 243, 258, 260 A, 267 J) bearing a number of spiral or verticillate stamens. The FEMALE FLOWERS are of a more varied structure (see the orders). The OVULE is orthotropous (except Podocarpus which is anatropous) and projects from the carpel uprightly, inverted, or horizontally; it has usually only one integument (compare however Taxaceæ) which proceeds from the upper part of the nucellus, so that the embryo-sac in part is placed below the integuments (Figs. 251, 264). The drop of mucilage which catches the pollen-grains dries up and draws the pollen-grain through the micropyle to a space just above the nucellus--the pollen-chamber--in which the germination of the pollen-grain commences.

In each seed, only one of the many embryos which are formed proceeds to its full development. The seed is always endospermous, and the embryo has one, two, or a whorl of several cotyledons. A vigorous primary root is developed on germination. THE VASCULAR BUNDLES in the stem are arranged in a ring, and increase in thickness takes place by a closed cambium-ring which forms bast (phlœem) externally, and wood (xylem) internally with distinct annual rings, as in the Dicotyledons. Only certain of the Cycadeæ deviate from this arrangement. The secondary wood is very uniform, as it is almost exclusively formed of tracheides with bordered pits, but true vessels are wanting; this also indicates a relationship with the Pteridophyta (see page 202).

The Gymnosperms are biologically lower than the Angiosperms; they are wind-fertilised, and without extra floral-nectaries.

This Division embraces three classes: CYCADEÆ, CONIFERÆ, And GNETEÆ. It is no doubt monophyletic, and has taken its origin from heterosporous Ferns, now extinct, most nearly related to the Ophioglossaceæ and Marattiaceæ. The Cycadeæ appear to be the oldest class. The Coniferæ are related to these through Ginkgo. The Gnetaceæ are more isolated. The Division is not continued into the higher Flowering-plants; it has evidently attained its highest development, and is now in a retrograde condition. The similarity which has often been pointed out between certain Coniferæ and Lycopodinæ is only in analogous resemblances, and does not entitle one to suppose that there is a nearer relationship, or that the former take their origin from the latter.

Class 1. =Cycadeæ.=

The stem is very rarely ramified. The leaves are large, pinnate, and arranged spirally. The flowers are diœcious, without perianth.

There is only one order, the =Cycadaceæ=.--In habit they resemble the Ferns, especially the Tree-Ferns (compare Figs. 207 and 256). The stem is tubercular (Fig. 258), or cylindrical (Fig. 256), but not very tall (as much as about 12 metres), and very rarely ramified. [In Ceylon, unbranched specimens of Cycas are rarely met with in the wild state. The stems of C. circinalis occasionally branch in greenhouses.]

The LEAVES are arranged spirally, and so closely together that no free stem-surface is left between them, and have only a slight sheath (which is not amplexicaul, as in the Palms). They are compound (most frequently pinnate; in Bowenia, bipinnate); in some genera the leaves are rolled up in various ways, resembling the vernation in Ferns (Fig. 257); they are leathery and perennial. In some, stipules are present, as in the Marattiaceæ. Groups of scale-leaves alternate in the majority with groups of foliage-leaves.

The FLOWERS are without perianth. The MALE FLOWER is sometimes an enormous collection of stamens (Fig. 258), which are flat in some (Cycas, Fig. 241), shield-like in others (Zamia, Ceratozamia) like the sporophylls in Horsetail (Fig. 259); but in all, the pollen-sacs are situated in large and varying numbers on the back of the stamens, and arranged in groups of 2–5, like the sporangia in the sori of the Ferns (Fig. 241 b, c). FEMALE FLOWERS are wanting in Cycas, because the carpels do not terminate the apical growth of the stem. After a group of foliage-and of scale-leaves, a group of carpels is developed, which are pinnate and resemble the foliage-leaves, bearing on their edges a number of ovules (most frequently 5–6) (Figs. 245, 256); the same stem produces successively scale-leaves, foliage-leaves, and carpels. The differentiation is not much more advanced than in certain Ferns (Struthiopteris, Blechnum), where barren and fertile leaves of different form regularly alternate. The other genera have female flowers; the carpels are shield-like in Zamia and Ceratozamia (Fig. 246), and collected into cone-like flowers, which terminate the growth of the stem (Fig. 259). The number of ovules in these instances is two to each carpel.

The SEEDS are large (most frequently 2–6 centimetres long) and plum-like; the external layer of the testa is fleshy, while the internal one is hard and horny. There are two systems of vascular bundles in the testa, one outside, the other inside the stone. The embryo is straight, attached to the end of the suspensor, which is often long, filamentous, and rolled up; it has one or two cotyledons.

The embryo in Ceratozamia and others is very slightly developed, at the time when the ripe seed is detached from the carpel; and it is not until after sowing that its further development and germination proceed. This calls to mind the Cryptogams, especially Selaginella, whose macrospores are thrown off filled with endosperm; but the oosphere is not fertilised till after the separation of the macrospore from the parent-plant, while in the Cycadeæ fertilisation is effected before the separation. In Cycas the testa may rupture, and the endosperm grow and become green in the light, even though no embryo has been formed. This also is an indication of its prothalloid nature.

Gum-passages are present in all organs. Collateral vascular bundles, with spiral and scalariform tracheides, are found; and normal thickening takes place by means of a cambium. An exceptional mode of growth is found in Cycas and Encephalartos, the cambium ceases to divide after a time and is replaced by a new cambium which arises in the cortical parenchyma just outside the bast, and which forms a new ring of xylem and phlœem. This may be repeated so that a number of concentric rings are produced. In Ceratozamia, structures resembling corals extend from the roots in a vertical direction and appear on the surface of the soil; these are peculiar roots, in which a symbiotic Alga (Anabæna) is found.

The Cycadeæ were formerly (from the Coal period to the Later Cretaceous) far more numerous than at the present day. They appear to have been most numerous in the Trias and Jurassic. The remnant (75 species) which have persisted to the present time are found in all tropical countries. Cycas (Trop. and Sub-trop., Eastern Hemisphere); Dioon (Mexico); Macrozamia (Australia); Encephalartos (Trop. and S. Africa); Stangeria (Fig. 258, Sub-trop. South and East Africa); Bowenia (Trop. Australia); Ceratozamia (Mexico, New Granada, Western Brazil); Microcycas (Cuba); Zamia (Trop. and Sub-trop. N. America.)

USES. Sago is made from the starch-containing pith of Cycas revoluta and circinalis. The leaves are often used at funerals and church festivals, under the name of “palm-branches.”

Class 2. =Coniferæ= (=Pine-trees=).

The stem branches freely. The leaves are entire, relatively small, linear or reduced to scales. The flowers are without perianth. The ovules naked. It is seldom that the female flower is reduced to only one carpel.

Whilst the Cycadeæ principally resemble the Ferns, the Conifers partly resemble the Lycopods, and partly the Equisetums--the former especially in the needle- or scale-like, leathery, simple, and often perennial leaves (“evergreen plants”), which never possess stipules (Figs. 263, 270, 272). Ginkgo deviates from this, being no doubt the oldest, and the Conifer which stands nearest to the Cycadeæ (Fig. 260). The resemblance to the Equisetums is especially owing to the fact that the stem ramifies abundantly, and often very regularly, forming a pyramid with verticillate branches. In addition to the foliage-leaves, scale-leaves (bud-scales) are present in the majority of species.

The FLOWERS are monœcious or more rarely diœcious. Perianth is wanting. The stamens of the catkin-like male flowers (Fig. 267, J) are of different forms, but as a rule more or less shield-like. As in the Cycadeæ, the pollen-sacs are in all cases situated on the underside. There are, as a rule, two pollen-sacs (the Abietaceæ, Fig. 267), or 3–5, (the Cupressaceæ and Taxaceæ, Fig. 243); a few have more, e.g. Araucaria (Fig. 242); they dehisce by clefts.

If, in commencing our consideration of the female flower, we begin with that of Ginkgo, we shall observe in the corner of a scale- or foliage-leaf a small flower, which consists of two carpels, each bearing one ovule, and reduced almost to the ovule itself (Fig. 260 C, D). The flower in Podocarpus is still further reduced, viz. to a single carpel with one ovule, which is anatropous and has two integuments. This ovule is situated in the axil of a cover-scale (c, in Fig. 262 D), and several female flowers of this description are collected in a small cone, the stalk and bracts of which become fleshy (Fig. 262 C). The external integument also becomes fleshy (an aril). Dacrydium, which is clearly related to Podocarpus, has an external integument which developes more independently as a fleshy aril (Fig. 262 B, B’). Microcachrys also is clearly allied to these: the bracts are more fleshy, and the ovule (i.e. the female flower) is protruded beyond the bract (Fig. 262 A, A’). Taxus stands in a more isolated position: a flower which has been reduced to an ovule is situated, in this instance, on the apex of a secondary branch which is studded with floral-leaves (Figs. 263, 264); an external integument is developed on all sides and surrounds the seed as a scarlet aril. According to this conception the aril corresponds to an external integument, and the Taxoideæ thus possess a partly dichlamydeous ovule. Only Ginkgo and Cephalotaxus appear to deviate from this, as in these there is only one integument (unless the small outgrowth indicated by ar, in Fig. 260 D, really is a rudimentary, external integument); in CYCADEÆ, to which Ginkgo is most closely related, there is likewise only one integument. But in these genera the testa is differentiated into two layers, and the seed resembles a drupe; like the Cycadeæ there is an external fleshy covering and an internal hard one, and these two layers may probably be considered homologous with the two integuments. This theory is also borne out by the arrangement of the vascular bundles in Cephalotaxus and Podocarpus, which present the xylem in the fleshy external layer to the outside of the testa, which is therefore the upper side of the integument (Celakovsky).

The coalescence of the integuments into one is only slight in Torreya, more pronounced in Podocarpus and strongest in Cephalotaxus and Ginkgo. Celakovsky terms these ovules “holochlamydeous.”

If we pass from these to the order PINOIDEÆ, we find the female flowers collected into catkin-like cones, which have been considered from various points of view to be sometimes single flowers, at other times compound inflorescences. The structure in ABIETACEÆ is as follows: a number of spirally arranged, scale-like leaves, cover-scales (Figs. 267, 268), are situated on a long axis. In the axil of each cover-scale a larger leaf-like projection, the ovuliferous scale, is borne, which turns the upper side towards its cover-scale (which is shown by the fact that the wood of its vascular bundles is turned downwards and towards the wood in the bundles of the cover-scale: Fig. 269). Two ovules, with micropyles turned towards the central axis, and with apparently only one integument (Fig. 268), are situated on the dorsal side of each ovuliferous scale, i.e. the side turned away from the cover-scale. The ovuliferous scales grow after fertilisation, into the woody or leathery “cone-scales,” which are usually much larger than the cover-scales. This ovuliferous scale with its axis may, according to Celakovsky, be considered as a dwarf-branch which is situated in the axil of the cover-scale, and bears two ovules (in the same way as in Ginkgo, one long-stalked flower, reduced to two ovules, is situated in the axil of a leaf), and in this case the external integument of the ovules is expanded into leaf-like bodies, which have united to form one “symphyllodium” (ovuliferous scale) which is inverted so that its dorsal side is turned upwards and bears the nucellus and the other integument (“hemichlamydeous” ovules). The carpel itself is therefore in this instance extremely reduced. The keel, or (in Pinus) “mucro” (Fig. 268 B), which is found in several genera, represents then a third carpel, which is sterile. In the other orders of the Pinoideæ the cover-scales and ovuliferous scales grow more and more together and finally form one structure, which also is termed a “cone-scale,” although from its development it cannot be homologous with the cone-scales of the Abietaceæ. This connation is least in the TAXODIACEÆ and ARAUCARIACEÆ and may be traced on the upper surface of the “cone-scale” by the presence of a stronger or slighter ridge or pad, the free portion of the ovuliferous scale (Figs. 256, 266, 269). It is most strongly pronounced in the CUPRESSACEÆ, in which the two scales form one single structure, the cone-scale (Fig. 274). The vascular bundles in the under portion corresponding to the cover-scale, have the xylem towards the upper side as usual in leaves, whilst the bundles present in the upper side of the cone-scale, which thus represents the ovuliferous scale, turn their xylem downwards. The hemichlamydeous ovules are then situated on the upper side of this cone-scale. According to this theory the CUPRESSACEÆ appear to be the youngest type, a view which corresponds with their vegetative structure. If there is only one ovule in these orders as in Agathis (Fig. 265) and Araucaria, then the flower is reduced to a single carpel and one ovule, as in the case of Dacrydium and Microcachrys. If two or more ovules are present, then the same number of carpels may be supposed to exist, the external integuments of their ovules being developed into leaf-like structures which collaterally coalesce to form a “symphyllodium,” or are suppressed.

According to this theory, which is based on the researches of Celakovsky, the female flowers of the Coniferæ may be classed thus:--

1. In all cases situated in the axil of a bract and collected into cones, with numerous flowers or with few or one flower. In Ginkgo only, are they situated in the axil of foliage- or scale-leaves.

2. It is only in Taxus that bracteoles are present.

3. They are formed only from rudimentary carpels, in which the stem takes no part.

4. The number of carpels in each flower varies from one to many, most frequently three, of which the central one remains sterile.

5. Each carpel bears only one ovule. The flower which is formed of only one carpel appears to consist of only one ovule.

6. The ovule has in Taxaceæ either a double integument (Podocarpeæ, Taxeæ), of which the external is the “aril,” or, as in the Cycadeæ, a single one, which is homologous with the two united together.

7. The external integument in the Pinoideæ is expanded to form a leaf-like structure--the ovuliferous scale--and bears on its dorsal side the ovules, which are thus only provided with one, and that the inner, integument.

This later interpretation of the female cones in the Coniferæ is more probably correct than the older ones; that, however, which appeared in the former issues of this book, may also be stated. It was to the effect that each catkin-like female cone is in reality a single flower; the cone-scales in the Cupressaceæ were single leaves, namely carpels, which bore the ovules on the side which is turned upwards; the division into two parts which makes its appearance in the other orders, and becomes most prominent in the Abietaceæ, was compared with the division of a leaf into a barren and a fertile portion, which is found especially in Ophioglossaceæ and Marsiliaceæ, or with the ligule in Isoëtes.

POLLINATION is accomplished by means of the wind. At the period of pollination the leaves are always so widely separated from one another, that the ovules can catch the pollen-grains carried to them by the wind; this is often effected by the mucilaginous drops which appear at the micropyle, and by the evaporation of which the pollen-grains are brought in contact with the nucellus. The entire cone grows considerably as soon as fertilisation has taken place, and the cone-scales in Pinoideæ close together so that the seeds while maturing are enclosed, and it is not until the seeds are ready for distribution that the cone-scales again become separated. In the Pinoideæ, the fully developed ovuliferous scales are hard and woody; and in this condition the collection of female flowers is termed a cone. In the Taxoideæ, true cones are the exception. 2–15 cotyledons are present, arranged in a whorl.

The characteristic feature of this class is the abundance of resin, which is to be found in isolated cells (especially in the cortex), partly in intercellular glands or passages (both in the cortex and wood). Taxus is the only genus which has no resin.

There are about 350 species, mostly from the Northern Temperate zone (especially North America and Siberia), where they grow gregariously and form the most northern forests. The Juniper, Scotch Fir, and Yew are natives of Great Britain.

This class may be divided into two families:--

1. =Taxoideæ.= The ovules have either one integument, the external part of which is fleshy, and the internal hard and stone-like; or two integuments, of which the external is the fleshy and coloured “aril.” “Ovuliferous scales” are wanting. The cones are never woody, but are generally succulent, the bracts become fleshy, or cones usually are not developed. The seeds project more or less freely beyond the bracts.

2. =Pinoideæ.= The ovules have two integuments, the external one of which is leaf-like and becomes developed as the “ovuliferous scale”; if there are several of these in each flower they unite and form a “symphyllodium.” This may remain free or unite with the bract. The cones are most frequently woody, rarely succulent. The seeds are hidden among the cone-scales.

Family 1. =Taxoideæ.=

This family, considered to be most nearly related to the Cycadeæ, also made its appearance at a very early period. There is only one order.

Order. =Taxaceæ.= The characters have been given above.

A. CEPHALOTAXEÆ is the oldest group, presumably the connecting link between the Cycadeæ and the other Coniferæ. The flower consists normally of two ovules. Aril wanting. One integument. Seeds drupaceous.--The flowers in Ginkgo biloba (Salisburia) are situated in the axil of foliage- or scale-leaves. The stamens bear only two pollen-sacs (Fig. 260 A). The female flower has two ovules, placed together at the end of a long, bare axis (Fig. 260 C). Round the base of the ovule a small collar (ar, in Fig. 260 D) is found, which may probably be considered homologous with the collar-like outgrowth which surrounds the base of the Cycas-ovule. The seed resembles a Plum, and has a fleshy external coat, surrounding a hard internal layer. The embryo is developed after the seed has fallen off. The Ginkgo-tree has long-stalked, fan-shaped leaves, more or less indented, with dichotomous veins resembling certain Ferns--the Adiantums. It is a native of East Asia, and the only surviving species of a genus which in earlier times was very rich in species, and distributed over the entire Northern Hemisphere. Cephalotaxus (Eastern Asia) is related to it.

B. PODOCARPEÆ. The female flower is reduced to one ovule, placed in the axil of a bract, or a little forward upon it. The ovule has an aril (2 integuments).--Phyllocladus (Fig. 261), from New Zealand and Tasmania, has obtained its name from its flat, leaf-like branches, the leaves proper being scale-like (f). The ovules stand erect in the axil of the scale-like leaves (c), and several are collected at the end of short branches.--Microcachrys tetragona (Tasmania) has a small female catkin with several spirally-placed, fleshy bracts, at the end of which the inward and downward turned ovule is attached (Fig. 262 A, A’). The ripe cones are red, succulent, and resemble Strawberries.--In Dacrydium (Tasmania, New Zealand, Malaysia) the female cone has most frequently only 1–2 (–6) bracts, which resemble the vegetative leaves; they have also a fleshy aril (Fig. 262 B, B’).--Podocarpus (40 species, East Asia, S. Temp.); the bracts of the female flowers become fleshy, and unite together; only 1 or 2 are of use in supporting the flowers. The ovules project high above the apex of the bract, and are anatropous, the micropyle being turned downwards (Fig. 262 C, D). An aril commences to develope in the flowering period as an external coating, and later on it becomes fleshy and coloured.

C. TAXEÆ. The female flower is reduced to one ovule, which is situated terminally on an axis which bears 2–3 pairs of opposite, scale-like bracteoles; on this account the Taxeæ form a very isolated group among the Coniferæ.--Taxus (T. baccata, the Yew-tree). Diœcious. The female flower consists of only one ovule, placed at the end of a short secondary branch (Fig. 264), which is studded with scale-like leaves. The aril when ripe is thick, fleshy, and scarlet (sometimes yellow), and only loosely envelopes the seed (Fig. 263). The leaves are scattered, flat, linear, and pointed (Fig. 263, 264). The short male flowers have 5–8 pollen-sacs, pendent from the stamens, and are surrounded at their bases by scale-like bracteoles (Fig. 243). Torreya (4 species, N. America and Japan) is closely allied to Taxus. The aril ultimately fuses with the woody inner integument, and hence the ovule becomes drupaceous, as in Cephalotaxaceæ.

USES. Taxus baccata is usually planted in gardens, especially in hedges. Its wood is very hard and is used for wood-carving. The shoots are poisonous, but not the aril, which is often eaten by children and by birds.

Family 2. =Pinoideæ.=

The four orders differ from one another partly in the arrangement of the leaves (Cupressaceæ have opposite or verticillately placed leaves, flowers, and inflorescences; in the others they are placed spirally), but chiefly in the greater or less degree of union which takes place between the female flower (the leaf-like “symphyllodium”) and its supporting cover-scale, and in the position of the ovules (the micropyle being turned upwards or downwards). The “cone-scales” in Abietaceæ are formed by “symphyllodia” alone, in the others by their union with the cover-scale.

Order 1. =Araucariaceæ.= This order most frequently has solitary ovules, turned downwards and attached to the centre of the cone-scales. In Agathis (Dammara) the arrangement is the most simple, a winged seed (Fig. 265), which hangs freely downwards, being borne in the centre of the undivided cone-scale. In Araucaria, the stamens with the free, pendulous pollen-sacs have been represented in Fig. 242; the ovuliferous scale is united for nearly its whole length with the bract, and projects from its apex in the shape of a sheath-like, dentate scale, resembling the ligule in Isoëtes, and may therefore be termed a “ligule.” Araucaria (S. America, Australia) has often rather broad leaves (A. brasiliensis). The ovuliferous scale in Cunninghamia is more distinct, and stretches transversely over the entire cover-scale; it bears three inverted ovules (Fig. 266) (Eastern Asia).

Dammara-resin, which is used for varnish, is obtained from Agathis (Dammara) species (New Zealand, Philippine Islands).

Order 2. =Abietaceæ (Pine and Fir Trees).= The leaves are spirally arranged and needle-like. The flowers are monœcious. The male flowers are long, and catkin-like, with numerous stamens, each bearing two oblong pollen-sacs. The pollen-grains are most frequently tri-lobed, having two bladder-like appendages, formed as outgrowths of the exospore, to assist in their distribution by the wind (Fig. 267 N). The bracts are arranged spirally. The union between the bract and the ovuliferous scale, which is found in the preceding order, is not in this instance so complete; these scales make their appearance as two free parts, and are attached only at their bases (Fig. 268); the lower portion, that is the cover-scale, in most instances remains quite small (Fir, Red Pine, and others), it is only in the “Noble Pine” (Abies) and Pseudotsuga douglasii, that it attains a greater length than the ovuliferous scale (Fig. 267, B-G). On the other hand the upper part, the ovuliferous scale (the vascular bundles of which have the bast turned upwards), grows strongly and elongates, especially after fertilisation, becoming woody or leathery; it is commonly termed the “cone-scale,” but is in reality only homologous with a part of the “cone-scale” in the other order of Pinoideæ. On the side of the ovuliferous scale, turned towards the axis, are situated two ovules with micropyles directed inwards. The seeds are most frequently provided with a false wing (a tissue-like part of the surface of the ovuliferous scale). Cotyledons, more than 2, verticillate. Fertilisation does not take place until some time after pollination. In Pinus, for instance, the pollen-tube only penetrates the nucellus for a short distance during the year of pollination, and then ceases its further growth, fertilisation not taking place until after the middle of the next year; whilst the seeds ripen about a year and a half after pollination. In the Larch and others, the seeds are mature in the autumn succeeding pollination.

Abies (Fir). The leaves are often (e.g. Ab. pectinata) displaced into 2 rows, flat and indented at the apex, with 2 white (wax-covered) lines on the under surface, in which the stomata are situated. The leaf-scars are nearly circular and do not project. The cones are erect. The cover-scales and the ovuliferous scales separate from the axis, to which they remain attached in other genera.--~Tsuga has leaves like Abies, but by the slightly projecting leaf-scars, and cones with persistent scales, it forms the transition to Picea.--Pseudotsuga has leaves similar to those of Abies and persistent carpels as in Picea, but the cover-scales grow as in Abies and project beyond the ovuliferous scales (P. douglasii, Fig. 267). These two genera are considered as sub-genera of Abies.~--Picea. The leaves project on all sides, square and pointed; the leaf-scars are rhombic, on projecting leaf-cushions. The cones are pendulous. The cover-scales are much shorter than the leathery, persisting ovuliferous scales.--The genus Larix (Larch) differs from all the others in having deciduous leaves (the three preceding have leaves which persist for eleven to twelve years). It has long-branches with linear foliage-leaves and short, thick, perennial dwarf-branches, which each year form a new rosette of foliage-leaves, similar to those on the long-branches. The male flowers and the erect cones resemble those of Picea, and are borne on dwarf-branches.--Cedrus (Cedar) resembles Larix to some extent, but has persistent leaves (C. libani, C. deodara).--Pinus (Pine) has long-branches and dwarf-branches. The leaves of the long-branches are scale-like and not green; the dwarf-branches have very limited growth, and persist for three years; they arise in the axils of the scales borne on the long-branches of the self-same year, and each bears 2–5 foliage-leaves, they are also surrounded at the base by a number of membranous bud-scales. The cone-scales have a thick, rhomboid extremity (the “shield”).

The buds which develope into long-branches arise at the apex of other long-branches, and being very close together, form false whorls. The female cones occupy the position of long-branches, and take about two years for their development. The male flowers arise close together, and form a spike-like inflorescence at the base of a long-branch of the same year. The male flowers occupy the position of dwarf-branches, so that a female cone may be considered to be a modified long-branch, and a male cone a modified dwarf-branch. The main axis of the seedling has needle-like leaves, similar to those found on the older parts, and on dwarf-branches; it is not until some time later that the dwarf-branches are developed and the permanent arrangement attained.

USES. Several species are commonly cultivated in this country, partly on heaths and moors, and partly in plantations and as ornamental trees, such as Mountain Pine (Pinus montana, Cen. Eur.); Austrian Pine (P. laricio, Eur.); Scotch Fir (P. silvestris, Eur.); Weymouth Pine (P. strobus, N. Am.); common Red Pine (Picea excelsa, Cen. and N. Eur.); White Pine (P. alba, N. Am.); Abies pectinata (Common Fir, S. and Cen. Eur); A. nordmanniana (Crimea, Caucasus); A. balsamea (N. Am.); Tsuga canadensis (N. Am.); Pseudotsuga douglasii (N.W. Am.); Larch (Larix europæa, Alps, Carpathians); L. sibirica (N.E. Russia, Siberia).--The wood of many species, especially Pine, on account of its lightness and because it is so easily worked, is very well adapted for many useful purposes. The wood of the Yew-tree is very hard and is used for ornamental turning. Resin and Turpentine (i.e. Resin with essential oils, the name being derived from the Terebinth-tree, from which formerly a similar material was obtained) are extracted from Pinus laricio and P. pinaster. Oil of Turpentine is obtained by distillation of turpentine with water; Tar by dry distillation of Pine-wood. Canada-balsam is from North American Abies-species (A. balsamea and Fraseri). The officinal Turpentine is mainly obtained from Pinus pinaster (South of France), P. tæda, australis, strobus (Weymouth Pine) and other North American species; more recently also from P. silvestris (Scotch Fir), maritima, laricio, Picea excelsa, and others; Venetian Turpentine, from Larch (S. Eur.) Amber is resin from a Tertiary plant (Pityoxylon succiniferum), closely related to the Pine, which grew especially in the countries round the South-East coast of the Baltic. Pinus pinea (the Pine, S. Eur.) has edible seeds and also P. cembra (in Cen. Eur. and Siberia).

Order 3. =Taxodiaceæ.= The vegetative leaves and cone-scales are arranged spirally. The ovules (2–9) are situated either at the base of the ovuliferous scales, in which case they are erect; or at their centre, when they are generally more or less inverted. The ovuliferous scale is more or less united with the cover-scale, and projects beyond the surface of the cone-scale, like a comb (Fig. 269). The vascular bundles, which extend into the cover-scale, have the usual leaf-arrangement, viz. the wood placed above the bast; while those bundles which enter the ovuliferous scale have this arrangement of the bundles reversed.

Taxodium distichum (the North American “Swamp Cypress”) has annual dwarf-branches, with distichous leaves, and cone-like “pneumathodia.” In the Tertiary period it was very common in the Polar regions. Sequoia (Wellingtonia) gigantea is the famous Californian Giant-Fir, or Mammoth-Tree, which attains a height of 300 feet, a diameter of 36 feet, and is said to live for 1,500 years. Cryptomeria japonica (Japan, China) has the least adnate ovuliferous scales; Glyptostrobus (China); Arthrotaxis (Tasmania); Sciadopitys verticillata (the only species in Japan) has, like Pinus, scale-like leaves on the long-branches, of which those which are situated at the apex of the annual shoots support “double needles,” i.e. dwarf-branches similar to the two-leaved dwarf-branches in Pinus, but without bud-scales, and with the two leaves fused together at the edges into one needle, which turns its upper surface away from the long-branch.

Order 4. =Cupressaceæ= (=Cypresses=). The leaves are opposite or verticillate, sometimes acicular, but most frequently scale-like (Fig. 270). In the species with scale-like leaves, the seedlings often commence with acicular leaves (Fig. 272), and branches are sometimes found on the older plants which revert to this form, seeming to indicate that the acicular leaf was the original form (atavism). The so-called “Retinospora” species are seedling-forms of Biota, Thuja, Chamæcyparis, which have been propagated by cuttings, and retain the seedling-form. The flowers are monœcious or diœcious. The male flowers are short, and have shield-like stamens, bearing most frequently several pollen-sacs. The cover-scales and ovuliferous scales are entirely fused together and form undivided cone-scales, opposite or whorled; the ovuliferous scales have slight projections near the base on which 1–2–several erect ovules are developed (Fig. 274). Most frequently 2 cotyledons.--Evergreen trees and shrubs.

Juniperus (Juniper). Diœcious. The cone-scales become fleshy and fuse together to form most frequently a 1–3 seeded “berry-cone.” ~J. communis (Common Juniper) has acicular leaves, borne in whorls of three, and the “berry-cone” is formed by a trimerous whorl of cone-scales (Fig. 273). J. sabina and J. virginiana have “berry-cones” formed from several dimerous whorls of cone-scales; the leaves are connate and opposite, needle-and scale-like leaves are found on the same plant.~

Cupressus (Cypress). Monœcious. The cones are spherical; the cone-scales shield-like, generally five-cornered and woody (Fig. 270), each having many seeds. The leaves are scale-like.--Thuja. Monœcious. Cones oblong. The cone-scales are dry, as in the Cypress, but leathery and imbricate, and not shield-like; each cone-scale bears 2–3 seeds. The leaves are most frequently dimorphic; those leaves which are situated on the edges of the flat branches are compressed, and only these bear buds, which are developed with great regularity, generally alternately, on both sides of the branch; those which are situated on the flattened surfaces are pressed flat and broad, and never bear branches (Fig. 271). Along the central line of each leaf there is a resin-canal (Fig. 271).--~Chamæcyparis, Callitris, Libocedrus, Thujopsis (1 species: T. dolabrata; in Japan).~

OFFICINAL. Juniperus sabina from Central and South of Europe (the young branches yield an essential oil). The wood of J. communis is used in the production of an essential oil, and J. oxycedrus in the production of empyreumatic oil. The “berry-cone” of J. communis is officinal, and is also used for gin.--The wood of J. virginiana (N. Am.) is known as red cedar, and is used for lead-pencils. Sandarack resin is obtained from Callitris quadrivalvis (N.W. Africa).

THE FOLLOWING ARE CULTIVATED IN GARDENS:--Thuja occidentalis (Arbor vitæ) (N. Am.), and orientalis (China, Japan); Juniperus sabina and virginiana; Thujopsis dolabrata (Japan); Cupressus lawsoniana (California), C. sempervirens (S. Eur., W. Asia), and other species, are grown especially in conservatories, and in Southern Europe particularly in cemeteries.--The Retinospora species which are so often planted, do not belong to an independent genus, but are obtained from cuttings, taken from seedling-plants with acicular leaves (see page 267).

Class III. =Gneteæ.=

This class, independent of extinct forms, comprises the most highly developed of the Gymnosperms, partly from the circumstance that a perianth of 2–4 members encloses the terminally placed ovule, which is provided with one, or (in Gnetum) two, integuments, and partly owing to the fact that the wood has true vessels. There is only one order.

Order. =Gnetaceæ.= The three known genera differ very much in appearance. Welwitschia mirabilis (from the deserts of South Western Africa) is the oldest (?) genus now living. It resembles a giant radish, in that the hypocotyl is the only part of the main axis of the stem which becomes developed. It attains a circumference of upwards of four metres with a length of 1/2½-⅔ of a metre. It bears only two oblong, leathery leaves (Fig. 275) which are torn into segments at the apex and lie on the surface of the soil; these are the two first foliage-leaves which succeed the cotyledons, and they are remarkable for their enormous length (upwards of two metres) as well as for their long duration, living as long as the plant itself. In their axils are situated the 4-rowed, spike-like male and scarlet-coloured female cones, upon dichotomous branches. The perianth consists in the ♂ of 2 alternating pairs of leaves, the inner ones of which are slightly united. The andrœcium likewise consists of 2 whorls: the external (transverse) with 2, the internal with 4 stamens; the lower halves of the 6 filaments uniting to form a cup. Each of the terminal anthers corresponds to a sorus of 3 sporangia, the sporangia being fused together, and opening at the top by one three-rayed cleft. In the centre of the ♂-flower there is a sterile ovule. In the ♀-flower a perianth of two connate leaves is present.--Ephedra (desert plants, especially in the Mediterranean and W. Asia) at first sight resembles an Equisetum; the stems are thin, long-jointed, and the leaves opposite, small, and united into a bidentate sheath; ♂-perianth of two connate leaves (median leaves); 2–8 stamens united into a column. Each anther is formed of 2 sporangia (is bilocular). ♀ mainly, as in Welwitschia. The seeds are surrounded by the perianth which finally becomes red and fleshy. There are 30 species.--Gnetum has opposite, lanceolate, pinnately-veined, leathery leaves. They are mostly climbers (Lianas) from Tropical Asia and America. The ♂-flowers have a tubular perianth, (formed from two median leaves) which surrounds a centrally-placed filament, bearing 2 anthers. In the ♀-flower there is a similar perianth, surrounding an ovule provided with 2 integuments. The perianth becomes fleshy and envelops the hard seed. 20 species.

From the circumstance of Welwitschia having ♂ flowers which, besides stamens, possess also a rudiment of an ovule, Celakovsky draws the inference that the earliest Gymnosperms had hermaphrodite flowers which from this structure became differentiated entirely into ♂-and ♀-flowers, with the exception of Welwitschia only, in which this differentiation was only carried out in the ♀-flower. This theory has so far been scarcely proved.

=Fossil Gymnosperms.=

The earliest continental plants which are known belong to the CORDAITACEÆ, a group of plants which existed as early as the Silurian period; they were Gymnosperms, but it has not yet been determined whether they were Cycads or Conifers. The CYCADS, even in the Coal period, were scarce; they attained their fullest development in Jurassic and Cretaceous periods, during which they were rich in species and genera, and extended as far as the Polar regions. In addition to these, Taxaceæ, Abietaceæ, and Taxodiaceæ appeared in the Carboniferous period. The TAXACEÆ appear to have attained their culmination in the Jurassic and Cretaceous periods; Ginkgo appears in the Rhætic; Torreya, in the Cretaceous; Taxus and Podocarpus in the Tertiary periods. The ABIETACEÆ also appear in the Carboniferous; Pinus was first known with certainty in the English Weald and in the Cretaceous; almost all other contemporary genera are represented in this latter period. The ARAUCARIACEÆ first appear, with certainty, in the Jurassic. The TAXODIACEÆ may be traced back as far as the Carboniferous (?); Sequoia is first found in the lowest Cretaceous, at that period it spread throughout the entire Arctic zone, and being represented by a large number of species, formed an essential part of the forest vegetation. Sequoia played a similar part in the Tertiary period. The CUPRESSACEÆ are first known with certainty in the Jurassic, but they appeared more frequently and numerously in the Tertiary period, in which most of the present living genera were to be found. The GNETACEÆ, according to a theory advanced by Renault were represented in the Coal period by the genus Stephanospermum, which had four ovules enclosed by an envelope.

DIVISION V.

ANGIOSPERMÆ.

See pages 3 and 224. To this Division belong the majority of the Flowering-plants. They are divided into two parallel classes, the Monocotyledons and the Dicotyledons, which differ from each other not only in the number of cotyledons, which, with a few exceptions, is one in the former, two in the latter, but also in the internal structure of the stem, the venation of the leaves, the number of the parts of the flower, etc. ~Assuming that these two classes have sprang from a common origin, it is amongst the Helobieæ in the first, and amongst the Polycarpicæ in the second class that we might expect to find closely allied forms, which might reasonably be supposed to have varied less from this original type. As for the rest, they seem to stand quite parallel, without exhibiting any close relationship. It is scarcely proved that the Monocotyledons are the older class.~

[Our knowledge of the forms included under the Angiosperms has recently been considerably increased by Treub (Ann. d. Jar. Bot. d. Buitenzorg, 1891), who has shown that the Casuarinas differ in many important points from the typical Angiosperms. Among other characters the pollen-tube is found to enter the ovule near the chalaza and therefore at the opposite end to the micropyle, and Treub therefore suggests that these plants should be placed in a subdivision termed Chalazogams.

According to this view the principal divisions of the Angiosperms would be represented thus:--

=Angiospermæ.=

Sub-division. Sub-division. CHALAZOGAMES. POROGAMES.

Class. Classes. Chalazogames. Monocotyledones, Dicotyledones.

More recently Nawaschin (Bull. Acad. Imp. Sci. St. Petersb., ser. iii., xxxv.) has shown that Betula, and Miss Benson (Trans. Linn. Soc., 1894) that Alnus, Corylus, and Carpinus also belong to the Chalazogams.

Our knowledge, however, is still so incomplete that one would hesitate to accord the full systematic value which Dr. Treub attaches to his discovery until the limits of the Chalazogamic group are better defined; and it would hardly be justifiable to include the Casuarinas and the above-noted genera in one family.]

Class 1. =Monocotyledones.=

The embryo has only one cotyledon; the leaves are as a rule scattered, with parallel venation; the vascular bundles of the stem are closed, there is no increase of thickness. The flower is typically constructed of five 3-merous whorls, placed alternately.

THE EMBRYO is generally small in proportion to the abundant endosperm (exceptions, see Helobieæ), and its single cotyledon is often sheath-like, and very large. On the germination of the seed either the entire cotyledon, or its apex only, most generally remains in the seed and absorbs the nutritive-tissue, while the lower portion elongates and pushes out the plumule and radicle, which then proceed with their further growth. The primary root in most cases soon ceases to grow, but at the same time, however, numerous lateral roots break out from the stem, and become as vigorous as the primary root, or even more so. Increase in thickness does not take place in these roots; they branch very little or not at all, and generally die after a longer or shorter time.

THE STEM is frequently a corm, bulb, or other variety of underground stem, as the majority of the Monocotyledons are perennial, herbaceous plants; it has scattered, closed vascular bundles (Fig. 276), and no cambium by which a continuous thickening may take place. The stem of the Palms, however, attains a very considerable thickness, which is due to the meristem of its growing-point continually increasing in diameter for a lengthened period (often for many years), until it has reached a certain size. In this condition the growing-point has the form of an inverted cone, and it is only when this cone has attained its requisite size that the formation of a vertical cylindrical stem commences. Certain tree-like Liliaceæ, as Dracæna, Aloe, etc., have a continuous increase in thickness; this is due to a meristematic layer, which arises in the cortex, outside the original vascular bundles, which were formed at the growing-point of the stem. This meristem continues to form thick-walled parenchyma and new, scattered vascular bundles. The primary vascular bundles, in the Palms and others, run in a curved line from their entrance into the stem at the base of the leaf, towards the centre of the stem, and then bend outwards and proceed downwards in a direction more parallel to the sides of the stem (Fig. 277). The bundles formed later, in those stems which increase in thickness, are not continued into the leaves.

THE BRANCHING as a rule is very slight, the axillary buds of the majority of the leaves never attaining development, e.g. in the Palms, bulbous plants and others. As the cotyledon arises singly, the succeeding leaves also must be scattered, but they are frequently arranged in two rows (Grasses, Iris, etc). The first leaf borne on a branch (the “Fore-leaf,”[24]--the bracteole, if on a floral shoot) has generally, in the Monocotyledons, a characteristic form and position, being situated on the posterior side of its own shoot, and hence turned towards the main axis; it is sometimes provided with two laterally-placed keels (Figs. 279 f, 290 øi), but the midrib is often absent. It arises in some cases from two primordia, which at the beginning are quite distinct, and thus has been regarded as formed by two leaves. It is, however, only one leaf, a fact which is evident from several circumstances, one being that it never supports more than one shoot, and this stands in the median plane (Fig. 279).

THE LEAVES are amplexicaul, and have a large sheath but no stipules; the blade is most frequently long, ligulate, or linear, entire, with parallel venation, the veins being straight or curved (Figs. 300, 309). Connecting the large number of veins which run longitudinally, there are as a rule only weak transverse ones. It is very rarely that other forms of leaves are found, such as cordate (Figs. 302, 312), or that the blade is branched, or the venation is, for example, pinnate or palmate (Figs. 225, 298); these deviations are especially found in the Araceæ, the Palms, the Scitamineæ (Fig. 308), the Dioscoreaceæ, and in several aquatic plants. The incisions in the Palm-leaf are derived by the splitting of an originally entire leaf.

THE STRUCTURE OF THE FLOWER is generally as follows: Pr3 + 3, A3 + 3, G3, rarely S3 + P3 with the other members unchanged.[25] Instead of 3, the numbers 2 and 4 may occur; rarely others. In all these instances there are 5 whorls, which regularly alternate with one another, most frequently in the 3-merous flower, as in the diagram (Fig. 278). This diagram is found in the following orders: Liliaceæ, Convallariaceæ, Juncaceæ, Bromeliaceæ, Amaryllidaceæ, Dioscoreaceæ, Palmæ, some Araceæ, and in some small orders, and may be considered as the typical structure and also the starting point for the exceptional orders. The ovary in many Monocotyledons has many ovules, and the fruit becomes a many-seeded berry or capsule; this form is no doubt the oldest. In others the number of seeds becomes reduced to 1, and the fruit then becomes a cypsela, or a drupe (e.g. Gramineæ, Cyperaceæ, Palmæ, etc).

Deviations from this typical floral structure in some instances may be traced to suppression, very rarely to a splitting of certain members, the typical relative positions not being changed. Thus, the Iridaceæ, the Cyperaceæ, most of the Gramineæ and some Juncaceæ deviate in having only 3 stamens (Fig. 279), the inner whorl (indicated by *) not becoming developed. The Musaceæ differ in the posterior stamen not being developed; Zingiberaceæ (Fig. 314), Marantaceæ, and Cannaceæ, in the fact that only 1 of all the stamens bears an anther, and the others are either suppressed or developed into petaloid staminodes, with some perhaps cleft in addition. The Orchideæ deviate in having, generally, only the anterior stamen of all the 6 developed (Fig. 280). In this, as in other instances, the suppression of certain parts of the flower is often connected with zygomorphy (i.e. symmetry in one plane), chiefly in the inner perianth-whorl, but also in the other whorls. In the Orchids, the perianth-leaf (the labellum, Fig. 280 l) which is directly opposite the fertile stamen, is larger and altogether different from the others. The perianth-leaves may also be suppressed; see, for example, the two diagrams of the Cyperaceæ (Fig. 284). In some orders the suppression of these leaves, which form the basis of the diagram, is so complete that it is hard to reduce the actual structure of the flower to the theoretical type, e.g. the Grasses (Fig. 290) and Lemna (Fig. 303). In the first family, which especially comprises water-plants, a somewhat different structure is found; thus Fig. 282 differs somewhat from the ordinary type, and other flowers much more so; but the floral diagrams which occur in this family may perhaps be considered as the most probable representatives of an older type, from which the ordinary pentacyclic forms have taken their origin. In favour of this theory we have the larger number of whorls, the spiral arrangement of some of these in the flower, with a large and indefinite number of stamens and carpels, the perfectly apocarpous gynœceum which sometimes occurs, etc., etc.

The Monocotyledons are divided into 7 Families:--

1. HELOBIEÆ. This family forms a group complete in itself. It commences with hypogynous, perfect flowers, whose gynœcium is apocarpous and terminates in epigynous and more or less reduced forms.

2. GLUMIFLORÆ. These have as a starting point the same diagram as the following families, but otherwise develope independently.

3. SPADICIFLORÆ. Also an independent branch, or perhaps two different ones which terminate in much reduced forms.

4. ENANTIOBLASTÆ. These ought perhaps to be amalgamated with the following family.

5. LILIIFLORÆ. These advance from forms with the typical diagram and hypogynous flower, to epigynous and reduced forms.

6. SCITAMINEÆ and

7. GYNANDRÆ. Two isolated families, which probably have taken their origin from Liliifloræ, and have epigynous, mostly zygomorphic, and much reduced forms.

Family 1. =Helobieæ.=

To this family belong only water- or marsh-plants; the endosperm is wanting, and they possess an embryo with a very large hypocotyl prolonged downwards and often club-like. The perianth is often differentiated into calyx and corolla; the flower is regular, and in the first orders to be considered, may be reduced to the ordinary Monocotyledonous type; there are, however, usually found two 3-merous whorls of carpels (Fig. 282), and thus in all 6 whorls, or again, the number of carpels may be indefinite; the number of stamens also may be increased, either by the division of the members of a whorl, or by the development of additional whorls. Syncarps,[26] with nut or follicular fruitlets, are very common, for example, in the first orders; in the last (Hydrocharitaceæ) the carpels are not only united, but the ovary is even inferior.

The primitive type appears to be a hypogynous flower, similar to that of the Juncaginaceæ or Alismaceæ, with several 3-merous whorls, and free carpels, each with many ovules; the green perianth in this instance being no doubt older than the coloured ones. If we take a flower with this structure as the starting point, then the family developes partly into epigynous forms, partly into others which are so strongly reduced and exceptional that it is scarcely possible to refer them to the ordinary type. The family, through the peculiar Zostereæ, appears to approach the Araceæ, in which Potamogetonaceæ and Najadaceæ are included by some authorities. However, the inclusion of Potamogeton, and with it Ruppia and Zannichellia, in the Juncaginaceæ appears quite correct. It would scarcely be right to separate Zostereæ from these. Great stress has often been laid upon the similarity with the Ranunculaceæ which is found in the Alismaceæ, but it is scarcely more than an analogous resemblance.

Order 1. =Juncaginaceæ.= The ☿, regular, hypogynous flowers have the perianth 3 + 3, sepaloid, stamens 3 + 3 (with extrorse anthers), and carpels 3 + 3 (free or united), of which last, however, one whorl may be suppressed (in Triglochin maritima all 6 carpels are developed, in T. palustris the inner whorl is unfertile). Inflorescence long spikes. Embryo straight.--Marsh-plants with radical, rush-like leaves, arranged in two rows, and often sheathing and ligulate (“squamulæ intravaginales”); the inflorescence is a spike or raceme.--Scheuchzeria. Carpels almost free; in each at least two ovules. Follicles.--Triglochin has long, fine racemes without bracts or bracteoles; one ovule in each carpel. The carpels in the two native species are united, but separate when ripe as a schizocarp, loosening from below; they open along the ventral suture or remain closed; a linear central column remains. ~The most reduced is Lilæa (1–2 sp. Am.)--Protogynous. About 10 species. Temp. Fossils in Tertiary.~

Order 2. =Potamogetonaceæ.= The aquatic plants belonging to this order are perennial, living entirely submerged, or with floating leaves, and preferring still water. The leaves are alternate, in some linear and grass-like, in others there is an elliptical floating blade, supported by a linear submerged petiole. Axillary scales. The fruit is generally a syncarp with nuts or drupes; the embryo is curved, of very various forms.

Potamogeton (Pond-weed). The rhizome is creeping, sympodial (with two internodes in each shoot-generation); the inflorescence is a terminal, many-flowered spike, without floral-leaves; below it are found 2 foliage-leaves placed nearly at the same height, from whose axils the branching is continued cymosely. The flowers are ☿, 4-merous, naked, and consist only of 4 stamens, with the connectives, broadly developed at the back of the anthers, resembling a perianth, and of 4 free, sessile carpels. They are common plants in fresh water. ~The spike, during the flowering, is raised above the water. Wind-pollinated and protogynous.--Closely allied is Ruppia (Tassel Pond-weed), in salt or brackish water. The spike has only two naked flowers, each consisting of 2 stamens and 4 carpels. The stalks of the individual carpels are considerably prolonged.--Zannichellia (Horned Pond-weed) is monœcious; the ♀-flower consists of 4 (2–9) carpels, with membranous, bell-shaped perianth; long styles; the ♂-flower has 1 (-2) stamens. Althenia.~

Zostera (Grass-wrack) is an entirely submerged, marine plant with creeping rhizome (with displacement of buds) and strap-shaped leaves. The flowering shoots are sympodia with displacement of the axes (Fig. 281). The inflorescence is a peculiar, flatly-compressed spike, on one side of which the flowers are borne (Fig. 281). ~This inflorescence may be considered, no doubt correctly, to be derived from the symmetrical spike of Potamogeton by strongly dorsiventral development, and by a strong suppression of the floral parts taking place simultaneously. Two rows of flowers are developed, but of these one is so pressed into the other that apparently only one is present.~ Each flower consists of only 1 stamen and 1 carpel situated at the same height (Fig. 281); the unilocular ovary encloses 1 pendulous ovule and bears a bifid style. As regards the perianth (?) one leaf may be present (Z. nana, Fig. 281 D). The pollen-grains are filamentous. Pollination takes place under water. ~Posidonia and Cymodocea are allied to these. About 70 species.~

Order 3. =Aponogetonaceæ.= Aquatic plants with tuberous stem. They have a single, petaloid perianth (3–2–1–leaved), most frequently 6 stamens and 3(-6) carpels. Straight embryo.--About 15 species (Africa, Madagascar, Tropical Asia and Australia).--Aponogeton distachyos and A. (Ouvirandra) fenestralis are grown in conservatories; the latter has lattice-like, perforated leaves.

Order 4. =Najadaceæ.= Only one genus Najas (about 10 species); annual fresh water plants with leaves in pairs and solitary, unisexual flowers. The ♂ flower is remarkable in having a terminal stamen, which has either 4 longitudinal loculi or 1 central one; on this account the stamen of Najas is considered by some authorities to be a stem and not a leaf-structure. The unilocular gynœceum and the single, erect, anatropous ovule are also terminal. Pollination takes place under the water.

Order 5. =Alismaceæ.= The regular, hypogynous flowers are in some species unisexual by the suppression of either andrœcium or gynœceum; they have a 6-merous perianth, generally differentiated into 3 sepals and 3 petals; generally 6 stamens in the outer whorl (by the division of the 3; Fig. 282) and often several 3-merous whorls inside these, and 6–∞ free carpels arranged cyclically or spirally. Fruit a syncarp.--Marsh- or water-plants with radical leaves and long-stalked inflorescences.

=A.= Butomeæ. Follicles with many seeds, which are borne on nearly the whole of the inner surface of the cyclic carpels (as in Nymphæaceæ). Embryo straight.--Butomus (Flowering Rush, Fig. 282), has an umbel (generally composed of 3 helicoid cymes). S 3, P 3, stamens 9 (6 + 3, i.e. the outer whorl doubled), G 3 + 3. ~B. umbellatus; creeping rhizome with triangular Iris-like leaves.--Hydrocleis. Limnocharis.~

=B.= Alismeæ. Fruit achenes. Latex common (in the intercellular spaces). The flowers are arranged most frequently in single or compound whorls. Embryo curved, horse-shoe shaped.--Alisma has S 3, P 3, A 6 (in 1 whorl, grouped in pairs, i.e. doubled in front of the sepals), and 1 whorl of 1-seeded achenes on a flat receptacle. The leaves are most frequently radicle, long-stalked; the lamina have curved longitudinal veins, and a richly branched venation. A. plantago.--Elisma (E. natans) has epitropous (turned inwards) ovules, whilst the ovules of Alisma, Sagittaria and others are apotropous (turned outwards).--Echinodorus (E. ranunculoides) has a convex receptacle, carpels many, united and capitate. Damasonium.--Sagittaria (Arrow-head) has monœcious flowers, several whorls of stamens and spirally-arranged achenes on a very convex receptacle. ~S. sagittifolia reproduces by tuberous buds formed at the end of long, submerged branches. The leaves, in deep and rapidly running water, are long and strap-shaped, but in the air arrow-shaped.~

Honey is secreted in the flower and pollination effected by insects. Alisma plantago has 12 nectaries. The submerged flowers of Elisma natans remain closed and are self-pollinated. Butomus has protandrous flowers. There are about 50 species, which mostly grow outside the Tropics.--Uses insignificant. The rhizome of some is farinaceous.

Order 6. =Hydrocharitaceæ.= This order differs chiefly from the preceding in its epigynous flowers. These are in general unisexual (diœcious), and surrounded by a 2-leaved or bipartite spathe; they are 3-merous in all whorls, but the number of whorls is generally greater than 5, sometimes even indefinite. The perianth is divided into calyx and corolla. The ovary is unilocular with parietal placentation, or more or less incompletely plurilocular. The fruit is berry-like, but usually ruptures irregularly when ripe. Embryo straight.--Most often submerged water-plants, leaves seldom floating on the surface. Axillary scales (squamulæ intravaginales).

Hydrocharis. Floating water-plants with round cordate leaves; S3, P3 (folded in the bud); ♂-flowers: 3 (-more) flowers inside each spathe; stamens 9–15, the most internal sterile. ♀-flowers solitary; three staminodes; ovary 6-locular, with many ovules attached to the septa; styles 6, short, bifid. [The petals of the ♀-flowers bear nectaries at the base. In this and the following genus the pollination is without doubt effected by insects.] ~H. morsus ranæ (Frog-bit) has runners; it hibernates by means of special winter-buds.~--Stratiotes; floating plants with a rosette of linear, thick, stiff leaves with spiny margin, springing from a short stem, from which numerous roots descend into the mud. Inflorescence, perianth, and ovary nearly the same as in Hydrocharis, but the ♂-flower has 12 stamens in 3 whorls, of which the outer 6 are in 1 whorl (dédoublement), and inside the perianth in both flowers there are numerous (15–30) nectaries (staminodes?). S. aloides (Water-soldier); in N. Eur. only ♀-plants.--~Vallisneria spiralis is a tropical or sub-tropical plant, growing gregariously on the mud in fresh water. The leaves are grass-like, and the plants diœcious; the ♂-flowers are detached from the plant, and rise to the surface of the water, where they pollinate the ♀-flowers. These are borne on long, spirally-twisted peduncles which contract after pollination, so that the ♀-flower is again drawn under the water, and the fruits ripen deeply submerged.--Elodea canadensis is also an entirely submerged plant. The leaves are arranged in whorls on a well-developed stem. Only ♀-plants in Europe (introduced about 1836 from N. Am). This plant spreads with great rapidity throughout the country, the reproduction being entirely vegetative. Hydrilla, Halophila, Thalassia, Enhalus.--In many of these genera the number of whorls in the flower is remarkably reduced; for example, in Vallisneria, in the ♂-flowers to 2: Pr 3, A (1-) 3, in the ♀ to 3: Pr 3, Staminodes 3, G 3.--About 40 species; Temp. and Trop.~

Family 2. =Glumifloræ.=

The hypogynous flowers in the Juncaceæ are completely developed on the pentacyclic, trimerous type, with dry, scarious perianth. Even in these the interior whorl of stamens becomes suppressed, and the ovary, which in Juncus is trilocular with many ovules, becomes in Luzula almost unilocular, but still with 3 ovules. The perianth in the Cyperaceæ and Gramineæ is reduced from hairs, in the first of these, to nothing, the flowers at the same time collecting more closely on the inflorescence (spike) supported by dry bracts (chaff); the number of stamens is almost constantly 3; stigmas linear; the ovary has only 1 loculus with 1 ovule, and the fruit, which is a capsule in the Juncaceæ, becomes a nut or caryopsis.--The endosperm is large and floury, the embryo being placed at its lower extremity (Figs. 286 B, 291).--The plants belonging to this order, with the exception of a few tropical species, are annual or perennial herbs. The stems above ground are thin, and for the most part have long internodes, with linear, parallel-veined leaves which have long sheaths, and often a ligule, i.e. a membranous projection, arising transversely from the leaf at the junction of the sheath and blade. The underground stems are short or creeping rhizomes. The flowers are small and insignificant. Wind- or self-pollination.

Order 1. =Juncaceæ= (=Rushes=). The regular, hermaphrodite, hypogynous flowers have 3 + 3 brown, dry, free perianth-leaves projecting like a star during the opening of the flower; stamens 3 + 3 (seldom 3 + 0) and 3 carpels united into one gynœceum (Fig. 283); the ovary is 3- or 1-locular; there is as a rule 1 style, which becomes divided at the summit into 3 stigmas, often bearing branches twisted to the right (Fig. 283). Fruit a capsule with loculicidal dehiscence. The embryo is an extremely small, ellipsoidal, cellular mass, without differentiation into the external organs.

Juncus (Rush) has glabrous foliage-leaves, generally cylindrical, rarely flat; the edges of the leaf-sheath are free (“open” leaf-sheaths) and cover one another. The capsule, 1- or 3-locular, with many seeds--Luzula (Wood-Rush) has flat, grass-like leaves with ciliated edges; the edges of the leaf-sheath are united (“closed” leaf-sheath). The capsule unilocular and 3-seeded.--Prionium: S. Africa; resembling a Tacona.

The interior whorl of stamens, in some species, disappears partially or entirely (J. supinus, capitatus, conglomerates, etc.)

Some of the numerous Juncus-species (e.g. J. effusus, glaucus, conglomeratus, etc.), have false, lateral inflorescences, the axis of the inflorescence being pushed to one side by its subtending leaf, which apparently forms a direct continuation of the stem, and resembles it both in external and internal structure. The foliage-leaves of this genus were formerly described as “unfertile stems,” because they are cylindrical, erect, and resemble stems, and consequently the stem was said to be “leafless”: J. effusus, glaucus, conglomeratus. Stellate parenchynatous cells are found in the pith of these stems and in the leaves. Other species have distinct terminal inflorescences and grooved leaves; J. bufonius (Toad-rush), compressus, and others. The inflorescences most often present the peculiarity of having the lateral axes protruding above the main axis. Their composition is as follows:--The flowers have either no bracteoles, and the inflorescences are then capitulate; or they have 1–several bracteoles. Each branch has then, first, a 2-keeled fore-leaf placed posteriorly (“basal-leaf”), and succeeding this are generally several leaves borne alternately and in the same plane as the basal-leaf, the two uppermost (the “spathe-leaves”) being always barren; those which lie between the basal-leaves and the spathe-leaves are termed “intermediate-leaves.” If only branches occur in the axils of the basal-leaves, then the succeeding branches are always borne on the posterior side of the axis, and form a fan[27]; if the basal-leaf is barren, and if there is only one fertile intermediate-leaf, then the lateral axes are always on the upper side, and a sickle[27]-like inflorescence occurs; if there are 2 fertile intermediate-leaves, then a dichasium is formed, and in the case of there being several, then a raceme, or spike.

Juncaceæ are, by several authors, classed among the Liliifloræ, but there are so many morphological and partly anatomical features agreeing with the two following orders, that they may, no doubt, most properly be regarded as the starting point of these, especially of the Cyperaceæ, which they resemble in the type of flowers, the inflorescence, the type of mechanical system, and the stomata.

POLLINATION by means of the wind. Cross-pollination is often established by protogyny. J. bufonius has partly triandrous and cleistogamic, partly hexandrous, open flowers.--DISTRIBUTION. The 200 species are spread over the entire globe, but especially in cold and temperate countries; they are seldom found in the Tropics.--USES. Very slight; plaiting, for instance.

Order 2. =Cyperaceæ.= The majority are perennial (seldom annual) herbs living in damp situations, with a sympodial rhizome and grass-like appearance. The stems are seldom hollow, or have swollen nodes, but generally triangular, with the upper internode just below the inflorescence generally very long. The leaves are often arranged in 3 rows, the leaf-sheath is closed (very seldom split), and the ligule is absent or insignificant. The flowers are arranged in spikes (spikelets) which may be united into other forms of inflorescences (chiefly spikes or racemes). The flowers are supported by a bract, but have no bracteoles. In some genera the perianth is distinctly represented by six bristles corresponding to six leaves (Figs. 284 A, 286 A); in others it is represented by an indefinite number of hairs (Fig. 284 B), and very frequently it is altogether wanting. The inner whorl of stamens is absent, and the flower has therefore 3 stamens (rarely more or less than 3), the anthers are attached by their bases to the filament (innate) and are not bifid (Figs. 286). Gynœceum simple, formed of 3 or 2 carpels; 1 style, which is divided at the extremity, as in the Juncaceæ, into 3 or 2 arms; the single loculus of the ovary contains one basal, erect, anatropous ovule; the stigmas are not feather-like. Fruit a nut, whose seed is generally not united with the pericarp. The embryo is small, and lies at the base of the seed in the central line, surrounded on the inner side by the endosperm (Fig. 286 B). On germination the cotyledon does not remain in the seed.

A regular perianth, with 6 scale-like perianth-leaves in 2 whorls, is found in Oreobolus. In Scirpus littoralis the perianth-leaves are spreading at the apex, and divided pinnately.

The branching of the inflorescence is often the same as in the Juncaceæ, and supports the theory that these two orders are related. In Rhynchospora and others, the “spikelets” are really only “spike-like” and to some extent compound.

=A.= SCIRPEÆ. HERMAPHRODITE FLOWERS.

1. Spikelets cylindrical, the bracts arranged spirally (in many rows). The lower ones are often barren, each of the others supports a flower.--Scirpus (Club-rush). The spikelets are many-flowered; the perianth is bristle-like or absent, and does not continue to grow during the ripening of the fruit (Fig. 286 A). Closely allied to this is Heleocharis, with terminal spikes.--Eriophorum (Cotton-grass) differs chiefly in having the perianth-hairs prolonged, and forming a bunch of white, woolly hairs (Fig. 284 B).

Cladium and Rhynchospora (Beak-rush) differs especially in the few-flowered, compound spikelets which are collected into small bunches; the latter has received its name from the fact that the lowermost portion of the style remains attached to the fruit as a beak.

2. Spikelets compressed, the bracts arranged only in two rows; the other characters as in the first-mentioned. Cyperus (spikelets many-flowered); Schœnus (Bog-rush); spikelets few-flowered; S. nigricans has an open sheath.

=B.= CARICEÆ. UNISEXUAL FLOWERS.

In the ♂-flowers there is no trace of a carpel, and in the ♀ no trace of a stamen. Floral-leaves in many rows. In some (Scleria, certain Carex-species), ♂-and ♀-flowers are borne in the same spikelet, the latter at the base or the reverse; in the majority each spikelet is unisexual.

Carex (Fig. 285) has naked, most frequently monœcious flowers. The ♂-spikes, which are generally placed at the summit of the whole compound inflorescence, are not compound; in the axil of each floral-leaf (bract) a flower is borne, consisting only of a short axis with three stamens (Fig. 285 A). The ♀-spikes are compound; in the axil of each floral-leaf is borne a very small branch (Fig. 285 D, a) which bears only one leaf, namely, a 2-keeled fore-leaf (utriculus, utr. in the figures) which is turned posteriorly (as the fore-leaves of the other Monocotyledons), and being obliquely sheath-like, envelopes the branch (in the same manner as the sheath of the vegetative leaves), and forms a pitcher-like body. In the axil of this leaf the ♀-flower is situated as a branch of the 3rd order, bearing only the 2–3 carpels, which are united into one gynœceum. The style protrudes through the mouth of the utriculus. ~The axis of the 2nd order (a in Fig. 285 D) may sometimes elongate as a bristle-like projection (normally in Uncinia, in which it ends as a hook, hence the name); this projection is in most cases barren, but it sometimes bears 1–several bracts which support male-flowers; this is normal in Elyna (or Kobresia) and Schœnoxiphium; the axis (a in 285 E) bears at its base a female-flower supported by the utriculus, and above it a male-flower supported by its bract.~

POLLINATION by means of the wind. Protogynous. Sometimes self-pollinated. The order embraces nearly 3,000 species, found all over the world. Carex and Scirpus are most numerous in cold and temperate climates, and become less numerous towards the equator. The reverse is the case with Cyperus and other tropical genera. They generally confine themselves to sour, swampy districts; some, on the other hand, are characteristic of sand-dunes, such as Sand-star (Carex arenaria). There are about 70 native species of Carex.

USES. In spite of their large number, the Cyperaceæ are of no importance as fodder-grasses, as they are dry and contain a large amount of silica; hence the edges of many of the triangular stems or leaves are exceedingly sharp and cutting. Cyperus esculentus has tuberous rhizomes, which contain a large amount of fatty oil and are edible (earth-almonds); it has its home in the countries of the Mediterranean, where it is cultivated.

Cyperus papyrus (W. Asia, Egypt, Sicily) attains a height of several metres, and has stems of the thickness of an arm which were used by the ancient Egyptians for making paper (papyrus). Some serve for plaiting, mats, etc. (Scirpus lacustris, etc.). Isolepis is an ornamental plant.

Order 3. =Gramineæ= (=Grasses=). The stems are cylindrical, generally hollow with swollen nodes, that is, a swelling is found at the base of each leaf which apparently belongs to the stem, but in reality it is the swollen base of the leaf. The leaves are exactly alternate; the sheath is split (excep. Bromus-species, Poa pratensis, P. trivialis, Melica, Dactylis, etc., in which the sheath is not split), and the edges overlap alternately, the right over the left, and vice versâ; the ligule is nearly always well developed. In general, the flowers are hermaphrodite; they are borne in spikelets with alternate floral-leaves, and the spikelets themselves are borne in either spikes or panicles. The two (seldom more) lowest floral-leaves in each spikelet (Fig. 289 øY, nY) are barren (as the covering-leaves in many umbels and capitula); these are termed the glumes. The succeeding floral-leaves, each of which supports one flower as its bract, are called the outer pales (nI); these sometimes each bear an “awn” (a bristle-like body which projects in the median line either from the apex or the back); sometimes the upper ones are barren. Each flower has a bracteole, which is placed on the inside opposite the main axis; it is thin, binerved or two-keeled, and never has an awn; it is known as the inner pale (øI). Immediately succeeding the bracteole are: (a) some small, delicate scales (lodicules, Figs. 287 D, 288 C, 290 L); (b) three stamens with anthers versatile, so as to be easily moved, and usually notched at each end (Fig. 287 C); and (c) a simple gynœceum formed of one carpel with two styles having generally spirally-branched stigmas (Figs. 287 D, 288 C). The ovary is unilocular, and contains one ascending or pendulous, anatropous ovule. Fruit a nut, whose seed is always firmly united with the thin pericarp (“caryopsis”). The embryo is larger than in the Cyperaceæ and is placed at the base of the seed, but on the outer convex surface of the pericarp (Figs. 287 I, 288 288 D, 291), outside the endosperm; plumule large with several leaf-primordia. On germination the cotyledon remains in the seed.

The majority of Grasses are annual or perennial herbs; tree-like forms being only found in the Tropics, for example, the Bamboos; they branch (in tufts), especially from the axils of the basal-leaves, while those which are borne higher on the stem are separated by longer internodes and have no vegetative branches in their axils, though a few forms, like Bambusa and Calamagrostis lanceolata, produce branches in these axils.

Only a few Grasses have a solid stem, such as Maize, Sugar-cane, and Andropogon. The blade is flat in the meadow-grasses, but the Grasses which live on dry places (“prairie-grass”) exposed to the sun, often have the blade tightly rolled up and almost filiform or bristle-like, with anomalous anatomical structure. A closed tubular sheath is found in Melica uniflora, Bromus-species, Poa pratensis and trivialis, Briza and some Glyceria-species. The sheath is developed for the purpose of supporting the young internodes while their growth is proceeding at the base. The “nodes” (the swollen joints which are seen on stems of Grasses) are not really part of the stem but are formed by the base of the leaf-sheath. They play a part in assisting the haulms to regain a vertical position when laid prostrate by wind or rain. The awn on the pale is homologous with the blade of the Grass-leaf, and the pale itself is the sheath. The arrangement of the leaves in the spikelet is similar to that in Cyperus and other Cyperaceæ, their floral-leaves being borne in several rows in Streptochæta. More than two barren “glumes” are found in Streptochæta, several Phalarideæ and others. The spikelets, too, are again arranged in two rows in the axils of suppressed floral-leaves. The inflorescence becomes a “compound spike” (ear) when the spikelets are sessile. In the majority of instances the spikelets are borne on long stalks; when these branch, then the secondary branches, and similarly all branches of higher order, are placed so far down upon the mother-axis that they all appear to be of equal value and to arise in a semicircle from the mother-axis itself, though in reality they arise from each other (Panicle, Fig. 288 A). Sometimes the main axis and branches of different orders unite together as in Alopecurus, Phleum, and some other Grasses, and hence the single (short-stalked) spikelets appear to arise singly and spirally, or without any definite order, directly from the main axis, with the production of a cylindrical inflorescence bearing “spikes” on all sides, that is, a “spike-like panicle.”--Many inflorescences are somewhat dorsiventral. The flower is rarely unisexual (Zea mais) or barren. Considerable difficulty is experienced in reducing the Grass-flower to the ordinary 3-merous Monocotyledonous type. Some authorities consider the lodicules, which are present in all Grasses but absent in the Cyperaceæ, to be homologous with a perianth. According to a more recent theory they are bracteoles, and hence the Gramineæ, like many of the Juncaceæ, have 2–3 bracteoles placed in two rows in the median plane. If this theory be correct, the flower is naked. The lodicules expand quickly and cause the opening of the flower (i.e. the two pales become separated from each other). Generally only 3 stamens belonging to the outer whorl are present (Fig. 290), as in Iris (Fig. 279), certain Juncaceæ and Cyperaceæ (Fig. 284), but in some, such as the Rice and certain species of Bamboos, all 6 are found. Pariana has more than 6. Only 1 of the carpels is present, namely, the anterior (of those in Fig. 284), so that the ventral suture and the place of attachment of the ovule are situated at the back of the ovary. The number of styles does not correspond with the number of carpels, and the styles may therefore be supposed to arise from the edges of the leaf to the right and left--a position which is not without analogy. In addition, a stylar projection is sometimes found on the anterior side and in the median line (e.g. in Phragmites), and the solitary style in Nardus has exactly this position; a similar arrangement is found in some species of Bambusa which have only one style; other species of Bambusa have three styles. A tripartite style is found in Pharus.

[The Grass-flower may be reduced to the ordinary Monocotyledonous type thus:--The outer pale is the bract of the flower since it bears in its axil the floral shoot; the inner pale occupies the customary position of the bracteole. The fact that it is binerved can be explained by its having been pressed against the main-axis during development. Similar binerved bracteoles are found in Iris (Fig. 279). These bracteoles in both Grass and Iris arise from single primordia, and are not produced by the coalescence of two leaves. The lodicules are the only parts of the perianth remaining, the outer whorl having been suppressed, and also the posterior leaf of the inner whorl; a posterior lodicule, however, is found in the Rice and some species of Bamboo. The outer whorl of stamens is usually absent, though this again is present in the Rice and Bamboo. The three carpels are reduced to one with two or sometimes three stigmas.]

THE FLOWERING. In the panicles the flowers open in basipetal order; the flowers in the spikes situated somewhat above the middle, commence to open first, and the flowering proceeds upwards and downwards. A few Grass-flowers never open (cleistogamic); Leersia oryzoides, Stipa-species, and e.g. Wheat and Rye in cold damp weather; some open their pales so wide that the anthers and stigmas may protrude at the top; most frequently the lodicules expand and force the pales suddenly and widely apart. The filaments elongate considerably, so that the anthers are pendulous and the stigmas unfold. In some Grasses e.g. Wheat, the blooming of each flower only lasts a short time. POLLINATION is generally effected by the wind. The Rye separates the pales very widely in the morning, and allows the anthers and stigmas to appear; it is almost entirely sterile when self-pollinated. The Wheat flowers at any time of the day, each flower lasting only a quarter of an hour. The pales open suddenly, but only half way, and the anthers scatter one-third of the pollen in their own flower and two-thirds outside. Self-pollination is effectual, but crossing gives better results. In Hordeum vulgare (all flowers ☿) the flowers of the 4 outer rows behave as in the Wheat, but those in the two central rows always remain closed. The ☿-flowers in the two central rows of H. distichum remain closed and fertilise themselves; they open exceptionally, and may be pollinated by the ♂-flowers in the 4 lateral rows. H. hexastichum is cleistogamic. Oats pollinate themselves.

The ripe Grass-fruit, in some species of Bamboo, is a berry; in some other Grasses a nut with loosely lying seed, in some even a capsule, but otherwise a “caryopsis.” In some instances it is loosely enveloped by the pales (Oat), in others firmly attached to these (Barley), and finally, in others, “naked,” i.e. it is entirely free from the pales (Wheat and Rye). On the ventral side there is a groove (Fig. 288 E); on the anterior side (dorsal suture), which is turned towards the inner pale, it is convex, and at the base on this side, inside the testa, lies the embryo (Fig. 288 D). The apex of the fruit is often hairy (Fig. 293). The skin (Fig. 291, a) is formed by the pericarp and testa, and in some cases (Barley) the pales also form the outer portion. The endosperm (b) is large, and formed of parenchymatous, starch-containing cells: aleurone (proteid) grains may also be found among them. When the starch-grains and the aleurone-grains adhere together the endosperm becomes “horny,” but is “floury” when the starch-grains lie loosely with air between them. In the most external region, just beneath the skin, 1–several layers of nearly cubical cells (filled principally with aleurone-grains and fat) are found, the aleurone-layer (Fig. 292). The embryo (Fig. 291 c-d) contains large quantities of fatty oil; the large shield-like structure, attached to the embryo and turned inwards towards the endosperm (c), is the cotyledon (scutellum); it remains enclosed in the seed during germination, and dissolves the endosperm by means of the peculiar epithelial cells developed on the dorsal surface. The radicle, on germination, is obliged to perforate a mass of cells derived from the suspensor and which form the “root-sheath” (coleorhiza, Fig. 293) round its base. In addition to the tap-root, lateral roots are frequently developed before germination; these quickly break through, and later on are followed by others which appear at the base of the leaf (Figs. 293, 294).

The DISTRIBUTION OF THE FRUIT is most frequently effected by the wind. The spirally-twisted and hygroscopic awn which persists on the fruits of some species (Avena, Stipa, etc.) assists in their dissemination, and even helps to bury them in the ground.

The two preceding orders are more closely related to each other than they are to the Gramineæ.

The generic differences are chiefly founded on the form of the inflorescence, the number and sex of the flowers in the spikelets, the shape and relative length of the pales, awns, etc. In addition to these the structure of the fruit and seed presents a great many differences; some have compound starch-grains, while in others they are single; some have 1 layer of aleurone-cells, others have several (Fig. 292), etc.

=1.= BAMBUSEÆ. Tall Grasses with woody, very siliceous stems which bear many branches in the axils of the leaves. 6 stamens. Bambusa (Bamboo).

=2.= ORYZEÆ. Oryza sativa (Rice) is a herbaceous marsh-plant, with panicle and small, 1-flowered spikelets, with two small glumes and two large, boat-shaped, strongly siliceous pales. 6 stamens.--Leersia. Lygeum. Pharus. Zizania aquatica.

=3.= MAYDEÆ. Zea mais (Indian-corn, Maize); the spikelets are unisexual; the ♂-spikelets in a terminal panicle; the ♀-spikelets closely crowded and arranged in many rows in a thick, axillary spike, enclosed by large sheathing-leaves. The ♀-spikelets are 1-(2-) flowered; the ovary bears one, long, filamentous style, with bifid stigma.--Euchlæna; Coix.

=4.= ANDROPOGONEÆ. Saccharum (Sugar-cane); the spikelets are exceptionally small, 1-flowered, and borne in pairs in many-flowered, long-haired panicles. Tall grasses with solid, sappy stem.--Andropogon.

=5.= FESTUCEÆ. Grasses with panicle (or spike-like panicle) and 2–several-flowered spikelets. Glumes small, in each case shorter than the spikelet.--Festuca (Fescue) and Bromus (Brome, Fig. 288) have the awn placed at the apex of the pale, or slightly below it. Festuca has perennial species, with only a sparsely-branched panicle with branches solitary or in pairs, and round spikelets; the leaf-sheath is widely open. Bromus has the branches borne in half whorls, and the leaf-sheath scarcely half open. Brachypodium has very short-stalked spikelets in a raceme.--Poa (Meadow-grass), Briza (Quaking-grass) and Glyceria have awnless spikelets; these in Poa are ovoid, compressed, and with sharply-keeled glumes; in Briza they are broad, cordate and drooping, with boat-shaped glumes; in Glyceria round, long, many-flowered, linear or lanceolate; some species of Glyceria have closed leaf-sheaths.--Dactylis (Cock’s-foot) differs from all others in the somewhat crowded and unilateral (subsecund) spikelets, which are compressed and oblique (i.e. one side more convex than the other).--Phragmites (P. communis, Reed); the lowermost flowers of the spikelet are ♂; its axis is covered with long, silky hairs; pales without awns, but acuminate. Perennial marsh-plants.--Melica; panicle small, sparsely-branched with round, awnless, few-flowered, usually drooping spikelets. The upper pales, with arrested flowers, are generally united into a club-like mass.--Molinia, Eragrostis, Koeleria, Catabrosa.--Cynosurus (Dog’s-tail) has a small, spicate panicle with unilateral spikelets, some of which are fertile, some barren, each supported by a pectinate scale. Arundo. Sesleria. Gynerium. Triodia.

=6.= AVENEÆ. Panicles with 2–many-flowered spikelets; at least one of the glumes is quite as long as the entire spikelet.--Avena (Oat). The pale is boat-shaped, often bifid, and at about the middle of the back has a twisted, bent awn.--Aira (Hair-grass) has a long-branched panicle with small, 2-flowered spikelets; the pale has a dentate apex and bears an awn on the posterior side close to the base.--Weingærtneria.--Holcus (Yorkshire-fog); a soft, hairy Grass with an open panicle, keeled glumes; 2 flowers in the spikelet, of which the lower one is ☿, the upper ♂; the pale which supports the ☿-flower has no awn, but that which supports the ♂-flower, on the contrary, is awned.

=7.= AGROSTIDEÆ. Panicles or spike-like panicles with 1-flowered spikelets. Generally 2 glumes and only 1 pale.--The following have PANICLES: Milium with square panicle-branches and round spikelets; Agrostis (Fiorin), with compressed, glabrous spikelets, whose glumes are longer than the pales. Calamagrostis differs in having a chaplet of long hairs at the base of the pale.--Stipa (Feather-grass) has a long, twisted awn.--The following have SPIKELIKE PANICLES: Phleum (Cat’s-tail, Timothy-grass) has sharply pointed, entirely free glumes, which are much longer than the awnless pales. Alopecurus (Fox-tail); glumes united below; pale with awn. Ammophila (Psamma). A. arundinacea; pales hairy at base; perennial, stiff-leaved, glaucous sand-grass with creeping rhizome. Aristida. Sporobolus.

=8.= PHALARIDEÆ. Panicles and spike-like panicles. The spikelet has in the upper part a single fertile flower; below it are placed 4 pales, of which the upper 1–2 sometimes support ♂-flowers. On the whole, 6 floral-leaves of the first order are present.--Phalaris (P. canariensis, Canary-grass) has an ovate, spike-like panicle, the spikelets are compressed, convex on the outer side, concave on the inner. The large glumes are winged on the back.--Digraphis (D. arundinacea) is closely allied to Phalaris, but the keel of the glumes is not winged.--Anthoxanthum (A. odoratum, Sweet-vernal) has a small, lanceolate, open, spike-like panicle; the spikelets have below 2 barren flowers, and above these an ☿-flower with 2 stamens. The upper glume is longer than the flower.--Hierochloa.

=9.= CHLORIDEÆ. The spikelets are arranged in the form of a spike in two rows on one side of an often flatly-compressed axis; they are mostly 1-flowered.--Chloris; Ctenium; Cynodon; Eleusine; Microchloa.

=10.= PANICEÆ. The spikelets are borne in panicles or spikes, which may be arranged like fingers or in a raceme. There is a centrally-placed ☿-flower; below it is sometimes a ♂-flower.--Panicum; Paspalum; Oplismenus; Setaria has an almost cylindrical spike-like panicle with several barren branchlets, which project as stiff, rough bristles.--Cenchrus; Pennisetum.

=11.= HORDEÆ. Spikes compound; spikelets sessile in the notches of a toothed axis.

=A.= Spikelets solitary.--Triticum (Wheat, Fig. 287) has in each tooth of the main axis, a several-flowered spikelet which turns its flat side towards the central axis. The cultivated species (true Wheat) are 1-2-annual, the wild ones (T. repens, Couch, also as an independent genus, Agropyrum) are perennial, with creeping rhizome and lanceolate glumes.--Lolium (Rye-grass) has in each tooth of the main axis a many-flowered, compressed spikelet, which is placed edgewise towards it and (with the exception of L. perenne) has only one outwardly-turned glume (L. temulentum has a rudiment of the inwardly-turned lower glume); the terminal spikelet has two glumes.--Secale (Rye). A two-flowered spikelet in each tooth; small, lanceolate, acuminate glumes. Nardus and Lepturus have very narrow spikes, the former with unilateral spikelets.

=B.= In each notch of the axis 2 or more spikelets are placed close together.--Hordeum (Barley). In each tooth three 1-flowered spikelets. H. hexastichum (6-rowed Barley), has 6 rows of fruits, since all the spikelets are fertile, and H. distichum (2-rowed Barley) 2 rows, since the lateral spikelets are (♂, and barren (p. 292).--Elymus has 2–6 many-flowered spikelets in each joint of the main axis. Ægilops has awns upon the glumes.

DISTRIBUTION. 315 genera with 3,500 species. The order is distributed over the whole world, and as regards number of individuals is perhaps the richest. In the Tropics, large, broad-leaved, tree-like forms are found (Bambuseæ, Olyreæ, Andropogoneæ, etc.; in S. Europe, Arundo donax); in England, next to the Compositæ, it is the order most rich in species (about 134).--The origin of some of the cultivated Grasses is lost in obscurity. The Maize, no doubt, was indigenous to America, where its nearest relatives are found, and where it has also been discovered in ancient Indian graves; Durra or Guinea-corn, Millet and Sugar-cane are South Asiatic plants, and our own cereals no doubt have sprung primarily from Western Asia and South-Eastern Europe (Barley from Armenia and Persia, where a very closely related wild species is found; Wheat from the same districts; Rye from the perennial species S. montanum). Panicum altissimum and Rice have come from Africa.

USES. The Grasses play a very important part as cereals and fodder plants. The following are the most important of the cultivated ones: Triticum vulgare (common Wheat), turgidum, amyleum, polonicum, spelta, durum, etc.; Secale cereale (Rye); Barley (Hordeum-species, see under the genus); Maize; Oats (Avena sativa, orientalis, nuda); Millet (Panicum miliaceum); Durra (Turkish Millet, or Guinea-corn, Sorghum vulgare, cernuum and saccharatum); Manna-grass (Glyceria fluitans). As fodder-plants especially: Rye-grass (Lolium perenne); Oat-grass (Avena elatior); Timothy (Phleum pratense); Fox-tail (Alopecurus pratensis); Cock’s foot (Dactylis glomerata); Dog’s tail (Cynosurus cristatus); Sweet-vernal (Anthoxanthum odoratum); Soft grass, or Yorkshire-fog (Holcus lanatus and mollis); Quaking-grass (Briza media); species of Meadow-grass (Poa); Fescue (Festuca) and Brome (Bromus).--Several cultivated species of Grass are also used in the preparation of fermented liquors, the starch in the seeds being transformed to sugar (beer from “Malt,” i.e. the germinated Barley; arrack from Rice); or the stem becomes specially saccharine before flowering: the Sugar-cane, Sorghum saccharatum.

OFFICINAL. The rhizome of Triticum repens, Oat-grain, flour of Barley, and the starch of Wheat, also sugar.

The seeds of Lolium temulentum are considered poisonous.--The stems of many species (including our common grains) are used in the manufacture of paper, especially “Esparto grass” (Stipa tenacissima) from Spain and N. Africa, and the sheathing-leaves of the ♀-spike of Maize. Sand Lyme-grass (Elymus arenarius), and especially Psamma arenaria, are important.--But few Grass-species are sweet-scented: Anthoxanthum odoratum and Hierochloa odorata contain coumarin; Andropogon-species have essential oils (“Citronella oil”).--ORNAMENTAL PLANTS are: the “Ribbon-grass” (a variety of Digraphis arundinacea), Stipa pennata (whose awn is exceedingly long and feathery), Gynerium argenteum (Pampas-grass), Lagurus ovatus, Hordeum jubatum, Bromus briziformis.

Family 3. =Spadicifloræ.=

The primitive form resembles that of the preceding family. In it we find the typical, perfectly developed, Monocotyledonous flower, sometimes even with free carpels and with a dry or somewhat fleshy, but never petaloid perianth; and this passes over into very different forms by the suppression of the floral-leaves, perianth and sporophylls (unisexual flowers are common), and by the close aggregation of the flowers in the inflorescence. The flower is hypogynous in every case. The inflorescence is a spike which may be either single or branched, and has often a thick and fleshy axis (a spadix). In Palms and Araceæ it is enveloped, at any rate prior to the opening of the flowers, by a very large floral-leaf, the spathe, which may be petaloid (Figs. 297, 301).

The fruit is most frequently fleshy (berry, drupe) or a nut, never a capsule. The embryo is small, with large, fleshy endosperm (Fig. 299 C); very rarely the endosperm is wanting.

The numerous plants belonging to this family are large, herbaceous or tree-like, and the leaves seldom have the usual Monocotyledonous form, i.e. linear with parallel venation, but most frequently have pinnate or palmate venation.

Order 1. =Palmæ (Palms).= The majority are trees with an unbranched, cylindrical stem, having short internodes and covered with leaf-scars or the bases of the leaf-stalks (Fig. 296), and at the summit a rosette of large leaves closely packed together (Fig. 295). An exception to this is found in Calamus (Cane, “Rotang”), whose thin, creeping or climbing stems have long internodes; sparsely[28] branched is, e.g. the African Doum-palm (Hyphæne). Notwithstanding their often enormous stems the Palms have fibrous roots, like the bulbous Monocotyledons. The leaves are pinnate (Feather-palms, Fig. 298) or palmate (Fan-palms, Fig. 295) and often very large; they have a well-developed petiole with an amplexicaul sheath, which is often more or less separated into a large number of fibres. In the bud the blade is entire but folded, as the leaf expands the lines of folding are torn, either those which are turned upwards (thus ∨ ∨ ∨ ∨, e.g. Pritchardia, Livistona, Phœnix, Chamærops) or those turned downwards (thus ∧ ∧ ∧ ∧, e.g. Cocos, Chamædorea, Calamus). The inflorescence is usually lateral; when, as in Sago-palm (Metroxylon rumphii) or Talipot (Corypha umbraculifera) it is terminal, the plant is monocarpic, and dies after flowering; it is often a very large and branched spadix with numerous flowers either borne externally or embedded in it, and enclosed either in one woody, boat-shaped spathe (Fig. 297) or several spathes, in the latter case one for each branch. The flowers are sessile or even embedded, regular, generally unisexual (monœcious or diœcious) with the usual diagram (Fig. 278); the perianth is inconspicuous, green or yellow, persistent, and more or less leathery or fleshy. 6, rarely 3 or many stamens. The 3 carpels remain either distinct or form one, generally 3-locular, ovary. The style is short. There is one ovule in each carpel. Often during ripening 2 carpels with their ovules are aborted. The fruit is a berry, drupe or nut, generally one-seeded, with a large horny or bony endosperm with hard thick-walled cells (e.g. Date-palm). In some (e.g. Cocoanut) it is thin-walled, soft, and oily; in several “ruminate.”

When germination commences in the Cocoanut, Date, etc., the apex of the cotyledon remains in the seed and developes into a spongy mass to withdraw the endosperm; in the Cocoanut it attains a considerable size (Fig. 299 C) and assumes the form of the fruit. The endosperm in the Cocoanut is hollow and the interior is filled with “milk.” In the Date-palm and the Vegetable-ivory (Phytelephas) the cell-walls of the hard endosperm serve as reserve material.

=1.= PHŒNICEÆ. Phœnix (Date-palm) has pinnate leaves with channeled leaflets and diœcious flowers with 8 free carpels, of which usually only one developes into a berry with membranous endocarp; the large seed has a deep furrow on the inner side, and horny endosperm.

=2.= SABALEÆ. These have fan-like leaves with channeled segments; flowers ☿ or polygamous, rarely diœcious, with 3 separate or only slightly united carpels, all of which are sometimes developed into fruits (berry or drupe, with thin stone).--Chamærops, the Dwarf-palm. The pericarp is externally fleshy, internally more fibrous, and provided with a membranous inner layer. The endosperm is ruminate (that is, the testa is several times deeply folded into the endosperm).--Sabal, Copernicia, Livistona (Fig. 298), Thrinax, Corypha, Brahea, and others.

=3.= COCOINEÆ. With pinnate leaves. Monœcious inflorescence. The carpels are united into a 3-locular ovary. The fruit is most frequently 1-locular, only 1 of the loculi becoming developed, rarely 3-locular; it is a drupe with a large, fibrous, external layer (mesocarp) and most frequently a very hard inner layer (endocarp, stone) which has 3 germ-pores, the 2 of these, however, which correspond to the suppressed loculi are closed; internal to the third lies the small embryo (Fig. 299). Endosperm containing abundance of oil. Cocos (the Cocoanut-palm), Attalea, Elæis, Acrocomia, Bactris.

=4.= LEPIDOCARYINÆ. The floral-leaves and flowers are borne in 2 rows on the spadix. The carpels are united into one 3-locular ovary; the fruit is coated by a layer of hard, shining, imbricate scales. The majority of the species are thorny, and climb by means of the thorny leaves. Some have fan-like (Mauritia), others pinnate leaves (Raphia, Calamus, Eugeissonia, Metroxylon; the stems of the latter die after the first flowering).

=5.= BORASSINÆ. Large Fan-palms without thorns, with 3-locular ovary. Drupe with separate stones. Latania and Lodoicea have many stamens; Hyphæne; Borassus (Palmyra-palm).

=6.= ARECINEÆ. The most numerous group. Feather-palms. Berry. Areca, Euterpe, Oreodoxa, Ceroxylon, Chamædorea, Geonoma, Caryota with bipinnate leaves.

=7.= PHYTELEPHANTINÆ. Flowers with rudimentary perianth united in close capitula. Phytelephas (Vegetable-ivory). Nipa.

DISTRIBUTION. About 1,100 species are known. In Europe only the Dwarf-palm (Chamærops humilis) is wild (Western Mediterranean). The Date palm (Phœnix dactylifera) belongs to North Africa and West Asia. Other African genera are Hyphæne (Doum-palm) and Elæis (E. guineensis, Oil-palm). A large majority of the genera are found in South America and in the East Indies. The following are AMERICAN:--Mauritia, Acrocomia, Bactris, Chamædorea, Oreodoxa, Euterpe, Attalea, etc. ASIATIC:--Metroxylon, Calamus, Areca, Borassus, Lodoicea (“Double-cocoanuts,” Seychelles) and others. The Cocoanut-palm has perhaps an American origin; all the other species of the same genus being endemic in America; it is the only Palm found on the coral islands of the Pacific Ocean, and is also the only one which is common to both hemispheres.

USES. Palms belong to the most useful plants; they contain no poison, and are of little medicinal interest, but are largely employed in the arts and manufactures, the hard timber being adapted for many purposes on account of the hard tissue in which the vascular bundles are embedded. “Cane” is the stem of Calamus-species (from India). SAGO is obtained from the pith of Metroxylon rumphii (Sago-palm, Sunda-Is., Moluccas), Mauritia flexuosa, etc. Sugar-containing sap (“palm wine”) is obtained from the American Mauritia vinifera and flexuosa, Borassus flabelliformis (Asiatic Palmyra-palm), Arenga saccharifera, etc., by cutting off the young inflorescences, or by perforating the stem before the flowering (arrack is distilled from this). Vascular strands for the manufacture of mats and brushes, etc., are obtained from the outer covering (mesocarp) of the Cocoanut, and from the detached leaf-sheaths of Attalea funifera (Brazil) (Fig. 296). WAX is yielded by the leaves of Copernicia cerifera (carnaueba-wax, Amazon region), and by the stem of Ceroxylon andicola (palm-wax, Andes); East Indian Dragon’s blood is from the fruit of Calamus draco; the young buds of many species, especially Euterpe, Cocos, Attalea, etc., are used as “cabbage.” Palm-oil is obtained from the oily mesocarp of the plum-like fruits of Elæis guineensis (W. Africa), and from the seeds, when it is largely used in the manufacture of soap. EDIBLE FRUITS from the Date-palm (Phœnix dactylifera, Arabia, Egypt, W. Africa), and the endosperm of the Cocoanut (Cocos nucifera). The seeds and the unripe fruits of the Areca-palm (Areca catechu) are chewed with the leaves of the Betelpeper, principally in Asia. VEGETABLE IVORY from the hard endosperm of Phytelephas macrocarpa (S. America.)--Many species are cultivated in the tropics as ornamental plants, but in this country only Chamærops humilis, Livistona australis and chinensis are generally grown. In addition to the few just mentioned, many others are of importance, but these are much the most useful.

Order 2. =Cyclanthaceæ.= This is a small order related to the Palms (44 species from Tropical America), with fan-like, folded leaves. The flowers are unisexual and arranged in whorls or close spirals on an unbranched spadix. Ovary unilocular, ovules numerous. To this belongs Carludovica palmata, whose leaves are used for Panama hats.

Order 3. =Pandanaceæ= (Screw-pines) is another small order, forming a transition to the Araceæ. The woody, (apparently) dichotomous stem is supported by a large number of aerial roots, which sometimes entirely support it when the lower portion of the stem has decayed. The leaves are closely crowded together, and arranged on the branches in three rows, which are often obliquely displaced, with the formation of three spiral lines; they are, as in the Bromeliaceæ, amplexicaul, long, linear, the edge and lower midrib often provided with thorns. The ♂-flowers are borne in branched, the ♀ in unbranched spadices or capitula, which resemble those of Sparganium, but have no floral-leaves. Perianth absent. The drupes or berries unite into multiple fruits.--About 80 species in the islands of the Indian Ocean.--Pandanus, Freycinetia.--Fossils perhaps in the chalk of the Harz.

Order 4. =Typhaceæ.= The flowers are unisexual, monœcious, and borne on a cylindrical spike or globose capitulum; ♂ inflorescences above, the ♀ below. The perianth consists of a definite number of scales (Sparganium), or in its place numerous irregularly-arranged hairs are found (Typha); in the ♂-flower there are generally three stamens; the gynœceum is formed of 1–2 carpels with 1 prolonged style; 1 pendulous ovule. The seeds are furnished with a seed-cover, which is cast off on germination.--The few species (about 20) which belong to this order are marsh plants with creeping rhizome (and hence grow in clusters); the leaves on the aerial shoots are borne in two rows, entire, very long and linear.

Sparganium (Bur-reed). The flowers are borne in globose capitula; the perianth distinct, generally consisting of 3 small scales; pistil bicarpellate. Drupe, dry and woody. ~The stalk of the lower ♀ capitula is sometimes united with the main axis, and consequently the capitula are situated high above their subtending-leaf.~

Typha (Bulrush, Reed-mace) has a long, cylindrical, brown spike, the lower portion bearing ♀-flowers, and the upper ♂-flowers, which is divided into joints by alternate leaves. The ♀-flowers have 1 carpel. The perianth is wanting, represented by a number of fine, irregularly-placed hairs; pistil unicarpellate. Fruit a nut.

The two genera, according to some, are related to the 2nd order. In both genera native species are found. The pollination is effected by the wind, and consequently the anthers project considerably, and the stigma is large and hairy. Typha is protandrous, Sparganium protogynous. The small, fine hairs surrounding the nut of Typha assist in its distribution by the wind.--Fossil Typhas in the Tertiary.

Order 5. =Araceæ= (=Arums=). The flowers are small, and always borne without bracts or bracteoles on an unbranched, often very fleshy spike, which is enclosed by a spathe, often petaloid and coloured (Fig. 301). The fruit is a berry. Outer integument of the seed fleshy.--The leaves have generally sheath, stalk, and blade with distinctly reticulate venation; they are chiefly cordate or sagittate (Fig. 302), seldom long with parallel venation as in the other Monocotyledons (Acorus, Fig. 300). The Araceæ are quite glabrous, generally perennial herbs with tubers or rhizomes. Many have latex.--For the rest the structure of these plants varies; for example, while some have a perianth, in others it is wanting; in some the perianth-leaves are free, in others united; some have hermaphrodite flowers, but the majority unisexual (monœcious); some have free, others united stamens; the ovules are orthotropous, anatropous, or campylotropous, erect or pendulous; the ovary is 1–many-locular; some have seeds with endosperm, others without. ~In habit there are great differences. While some, e.g. Colocasia (Fig. 302), have a thick, more or less upright stem, with leaf-scars, but not woody, others are climbers, epiphytic, and maintain themselves firmly by means of adventitious roots, on the stems and branches of trees, or even on steep rocks, e.g. Philodendron; the cordate, penninerved leaf is the most common (Fig. 302), but various branched forms appear; the pedate leaves of Helicophyllum, Dracunculus, etc., are cymosely branched; the leaves of Monstera deliciosa, perforated by tearing, should be noticed (the vascular bundles while in the bud grow faster than the tissue between them, causing the latter to be torn, and the leaf perforated). With regard to the anatomical structure, the presence or absence of latex, raphides, resin-passages, groups of mucilage-cells should be noted. Engler makes use of these anatomical peculiarities for a scientific arrangement of the order.~

=A.= ORONTIEÆ, CALAMUS-GROUP. ☿, hypogynous flowers of a completely formed monocotyledonous type (number in the whorls 2, 3, or 4).--Acorus (A. calamus, Sweet-flag) has a regular, 3-merous, pentacyclic flower (Fig. 300 C, D). They are marsh-plants, with creeping rhizome, triangular stem, and long, sword-like leaves (Fig. 300 A); the inflorescence is terminal, apparently lateral, being pushed to one side by the upright, sword-like spathe (Fig. 300 B).--~Anthurium (Pr2+2, A2+2, G2); Pothos; Orontium (unilocular ovary with one ovule), etc.~

=B.= CALLEÆ. Flowers hypogynous, naked, ☿.--Calla (C. palustris). All flowers in the spike are fertile, or the upper ones are ♂; 6–9 stamens; ovary unilocular with many basal ovules. Marsh-plants with creeping rhizome and cordate leaves.--Monstera, Rhaphidophora, etc.

=C.= ARINEÆ. Flowers monœcious, naked, ♂-flowers on the upper, ♀ on the lower part of the spadix.--Arum (Fig. 301). The spadix terminates in a naked, club-like portion (k); below this is a number of sessile bodies (rudimentary flowers), with broad bases and prolonged, pointed tips (b); underneath these are the ♂-flowers (m), each consisting only of 3–4 short stamens, which eject vermiform pollen-masses through the terminal pores; then follow, last of all, ♀-flowers (f), each of which consists of one unilocular ovary, with several ovules. Perennial herbs, tuberous, with cordate leaves.--~Dracunculus; Biarum; Arisarum; Pinellia (Atherurus) ternata with leaves bearing 1–2 buds. Zantedeschia æthiopica (Richardia, Nile-lily); ♂, 2–3 stamens; ♀ with 3 staminodes, 1–5-locular ovary (S. Africa.)--In some genera sterile flowers are present between the ♂ and ♀ portions of the spadix (e.g. in Philodendron); in Ambrosinia a lateral, wing-like broadening of the axis of the spadix divides the cavity of the spathe into two chambers, the anterior containing one ♀, and the posterior 8–10 ♂-flowers in two series; in some the stamens in the single ♂-flowers unite and form a columnar “synandrium” (e.g. in Dieffenbachia, Colocasia, Alocasia, Caladium, Taccarum, Syngonium). A remarkable spadix is found in Spathicarpa; it is united for its entire length, on one side, with the spathe, and the flowers are arranged upon it in rows, the ♀ to the outside, and the ♂ in the middle (Zostera has a similar one).--Pistia similarly deviates considerably, it is a floating water-plant, with hairy, round rosettes of leaves; in it also the spathe and spadix are united; at the base a ♀-flower is borne, which consists of one unilocular ovary, and above several ♂-flowers, each composed of two united stamens.~

BIOLOGY. The inflorescences are adapted for insect-pollination; they are protogynous, since the viscous, almost sessile stigmas come to maturity and wither before the pollen, which is generally dehisced by apical pores, is shed; some pollinate themselves freely by the pollen from the higher ♂-flowers falling upon the ♀-flowers below them, and in some it is conjectured that the pollination is effected by snails. The coloured spathe, and the naked end of the spadix (often coloured) of certain genera function as the coloured perianth in other orders; during flowering a very powerful smell is often emitted. Arum maculatum is worthy of notice; small flies and midges creep down into the spathe, between the sterile flowers (Fig. 301 b), which are situated where the spathe is constricted, and pointing obliquely downwards prevent the escape of the insects; in the meantime, the stigmas are in a condition to receive any pollen they may have brought with them; after pollination the stigmas wither, and exude small drops of honey as a compensation to the flies for their imprisonment; after this the anthers (m) open and shed their pollen, the sterile flowers wither, and the insects are then able to escape, and enter and pollinate other inflorescences.--In many, a rise of temperature and evolution of carbonic acid takes place during flowering; a spadix may be raised as much as 30°C. above the temperature of the surrounding air.--Again, under certain conditions, many species absorb such large quantities of water by their roots that water is forced out in drops from the tip of the leaf; this may often be observed in Zantedeschia.

About 900 species in 100 genera. Home, the Tropics, especially S. America, India, and the Indian Islands, preferably in shady, damp forests growing as epiphytes upon trees, and on the banks of streams. Outside the Tropics few are found. Acorus calamus was introduced into Europe from Asia about 300 years ago; it, however, never sets any fruit, as the pollen is unfertile. In England Arum maculatum is a very common plant; this and A. italicum are the only native species. Colocasia antiquorum comes from Polynesia and the Indian Islands, and also Alocasia macrorrhiza. Fossils in Cretaceous and Tertiary.

USES. Many species have pungent, and even poisonous properties (e.g. Dieffenbachia, Lagenandra, Arum), which are easily removed by boiling or roasting; the rhizomes of many species of Caladium, Colocasia (C. antiquorum, esculenta, etc.), are very rich in starch, and in the Tropics form an important source of food. An uncommon occurrence in the order is the highly aromatic rhizome of Acorus calamus; this contains calamus-oil and acorin which are used in perfumery. Many are ornamental plants, e.g. Zantedeschia æthiopica (South Africa), generally known as “Calla,” and Monstera deliciosa; many other species are grown in greenhouses.

Order 6. =Lemnaceæ (Duck-weeds).= These are the most reduced form of the Spadicifloræ. They are very small, free-swimming water-plants. The vegetative system resembles a small, leaf-like body (Fig. 303 f-f), from which roots hang downwards; this branches by producing a new, similar leaf-like body, which springs from a pocket-like hollow (indicated by a dotted line in the figure) on each side of the older one, at its base (or only on one side). ~The branching is thus dichasial or helicoid (Fig. 303 A, where f, f′, f″, f″′ indicate shoots of 1st, 2nd, 3rd, 4th generations respectively). The leaf-like bodies are, according to Hegelmaier, leaf-like stems, and thus Lemna has no other leaves than the spathe and the sporophylls; according to the investigations of Engler they are stems whose upper portion (above the “pocket”) is a leaf, which is not sharply separated from the underlying stem-portion. The inflorescence is a very much reduced Araceous-spadix, consisting in Lemna of 1 or 2 stamens of unequal length (1-stamened ♂-flowers), 1 unilocular carpel (♀-flower), and 1 thin spathe (B). [The same is found in Spirodela polyrrhiza, etc., whose daughter-shoots begin in addition with 1 basal-leaf. Wolffia arrhiza, etc., have no roots, no spathe, and only 1 ♂-flower in the inflorescence (Engler).]--On the germination of the seed a portion of the testa is thrown off as a lid, so that an exit is opened for the radicle.--19 species. In stagnant fresh water, both Temp. and Tropical.--In Europe the species are Lemna minor, trisulca, gibba; Spirodela polyrrhiza, and Wolffia arrhiza, the smallest Flowering-plant.~

Family 4. =Enantioblastæ.=

The flowers in this family are hypogynous and have in part the general monocotyledonous type with 5 trimerous whorls completely developed in a regular hermaphrodite flower, and in part the flowers so much reduced that the type is very difficult to trace. On the one hand the family is well developed and has capitate inflorescences (Eriocaulaceæ) and on the other hand it is distinctly reduced (Centrolepidaceceæ). This family has taken its name from the fact that the ovule is not, as in the Liliifloræ and nearly all other Monocotyledons, anatropous, but orthotropous, so that the embryo (βλάστη) becomes placed at the end of the seed opposite (ἐναντίος) to the hilum. Large, mealy endosperm.--The orders belonging to this family are by certain authors grouped with the Bromeliaceæ and Pontederiaceæ, etc., into one family, FARINOSEÆ, so named on account of the mealy endosperm, the distinguishing character of the Liliifloræ then being that the endosperm is fleshy and horny.

Order 1. =Commelinaceæ.= The complete Liliaceous structure without great reductions in the number of whorls, but with generally few ovules in each loculus of the ovary, is found in the Commelinaceæ, an almost exclusively tropical order with about 317 species; herbs, some of which are introduced into our gardens and greenhouses. The stems are nodose; the leaves often clasping; the flowers are arranged in unipared scorpioid cymes, often so that they form a zig-zag series falling in the median line of the bracts, and after flowering they bend regularly to the right or left, outwards or inwards. They are more or less zygomorphic, particularly in the stamens, which in the same flower are of different forms or partially suppressed. The outer series of the perianth is sepaloid, the inner petaloid, generally violet or blue; the filaments are sometimes clothed with hairs formed of rows of bead-like cells (well known for showing protoplasmic movements). Fruit a trilocular capsule with loculicidal dehiscence (generally few-seeded); in some a nut. The radicle is covered by an external, warty, projecting covering which is cast off on germination.--The abundant raphides lie in elongated cells whose transverse walls they perforate.--Commelina, Tradescantia, Tinantia, Cyanotis, Dichorisandra.

Order 2. =Mayacaceæ.= This order is closely allied to the Commelinaceæ. 7 species. American marsh- or water-plants.

In many of the following orders of this family the flowers are united into compound inflorescences, with which is accompanied a reduction in the flower.

Order 3. =Xyridaceæ= (50 species). Marsh-plants with radical, often equitant leaves arranged in 2 rows, and short spikes on long (twisted) stalks. The flowers, as in the Commelinaceæ, have sepals (which however are more chaffy) and petals, but the outer series of stamens is wanting. Capsule (generally many-seeded).

Order 4. =Rapateaceæ.= Marsh-plants with radical leaves, usually in two rows, and several spikelets on the summit of the main axis, clustered into a capitulum or unilateral spike. Each spikelet has numerous imbricate floral-leaves and one flower. 24 species. South America.

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