Plant-life, with 74 full-page illus., 24 being from photos, by the author and 50 in colour from drawings

Front matter

ALBERT R. MANN LIBRARY AT CORNELL UNFVERSITY

Cornell University

Library

Preface

Tue author has endeavoured in this volume to present his readers with a clear account of plant life in its whole gamut, from the simplest microscopic forms to the most specialized flowering plants. It is hoped that the result of his efforts may be of some value to the amateur botanist and the lover of nature. It may also happen that this book will prove to be a useful, easy introduction to the study of more technical works. Technical terms, which are the intellectual currency of the botanist, and imply in a single word or phrase what would be explained only in long sentences, have not been entirely avoided. Indeed, the author has been compelled to use a considerable number, but an effort has been made to lead up to their use in easy sequence, and to explain as tersely and clearly as possible what they mean. The glossarial index will assist the reader in discovering where the meanings of terms are explained. The early chapters deal with the so-called cryptogamic plants, and the author trusts that what he has set down anent them may lead the amateur botanist, who has hitherto given attention solely to flowering Vv vi PREFACE species, to take them into consideration, and make a study which cannot fail to add to his pleasure in the field. Besides, if one is to catch the real spirit of botany, and in any way grasp the principles of plant-life, these humbler plants must be taken into account. It is within their ranks that we get to the foundation of things, and they display phenomena that throw considerable light on the beginnings and earliest developments of plants.

According to a Hindoo proverb, “ The carpenter is forgotten when the house is built.””. The author is not unmindful of the painstaking labours of a host of observers who have contributed to the fabric of modern botany. He has entered into a heritage of knowledge upon which he has freely drawn in confirming and supplementing his own observations. If he makes no pointed acknowledgments, it is because the workers to whom he is indebted are too numerous, not that he is ungrateful.

The coloured plates are from drawings by Mr. C. F. Newall; they are distinguished for a degree of accuracy made certain by the fact that Mr. Newall is a botanist as well as an artist. The black-and-white plates are from the author’s own photographs.

CHARLES A. HALL.

MEIKLERIGGS, PAISLEY, 1915.

Chapter I Introductory—asexual Plants - - - - 1

PAGE

CHAPTER II THE DEVELOPMENT OF SEX IN PLANTS AND A STUDY IN EvoLUTION- 28

CHAPTER III SEAWEEDS = 2 3 : - 69 CHAPTER IV Foner anp LicHENS - - - 90 CHAPTER V THE ARCHEGONIATES: I. BRYOPHYTES—LIVERWORTS AND MossEs - 120 CHAPTER VI THe ARCHEGONIATES: II. PreRIDOPHYTES—FERNS, HORSETAILS, anD CiUB-MossEs - - - - - - 142 CHAPTER VII PHANEROGAMIA: FLOWERING PLANTS - W71 CHAPTER VIII - < - - 219

Fosstu PLants - - vii

Vill

Tue Foop oF PLANTS, AND HOW THEY SECURE IT

CONTENTS

CHAPTER IX

CHAPTER X

THE PERPETUATION OF THE RACE -

CHAPTER XI

Tue DEFENCES OF PLANTS - .

Econoey :

CHAPTER XII

THE NEw FirLtp Botany

PAGE

LIST OF FULL-PAGE PLATES IN COLOUR AND BLACK AND WHITE

PHOTOGRAPHIC PLATES ARE MARKED WITH AN ASTERISK.

PLATE

I. Common Mallow (Malva sylvestris) Frontispiece

TO FACE PAGE

II. Some Fresh-Water Alge - 32 *TIT. Fungus (Coprinus atramentarius) - - - - 96 IV. Liverwort (Marchantia); Moss (Funaria) - - 124 *V. Parsley Fern (Cryptogramme crispa) 137 *VI. Common Polypody Fern (Polypodium vulgare) - - 144 VII. Corn Horsetail (Hquisetum arvense) 158 VIII. Marsh Marigold (Caltha palustris) - - - 171 IX. Greater Spearwort (Ranunculus lingua) - - 174 *X. Scots Pine (Pinus sylvestris) 177 *XT. Scots Pine, Male and Female Flowers 184 XII. Broad-leaved Garlic (Alliwm ursinum) - 193 XIII. Common Arum (Arum maculatum) - 196 XIV. Flowering Rush (Butomus umbellatus) — - 198 XV. Tway-blade Orchis (Listera ovata) 200 XVI. Sweet-Scented Orchis (Habenaria conopsea) 202 XVII. Marsh Orchis (Orchis latifolia) - 204 *XVIII. Sweet Cicely (Myrrhis odorata) - 208 *XIX. Hedge-Convolvulus, or Bindweed (Calystegia sepium) 209 XX. Henbane (Hyoscyamus niger) - - - 211 XXI. Corncockle (Agrostemma Githago) - - 212 XXII. Sea-Campion (Silene maritima) - 214 ix x

PLATE

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XXVII.

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XXX. *XXXI. *XXXII. *X XXIII.

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*XLVI. *XLVITI.

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a Bs LI. *LI.

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LV.

LIST OF FULL-PAGE PLATES

TO FACE PAGER

Greater Celandine (Chelidonium majus) . 216 Cuckoo-Flower (Cardamine pratensis) 217 Sea-Milkwort (Glaua maritima); Brookweed (Samolus Valerandi); Bog-Pimpernel (Anagallis tenella) 219 Evergreen Alkanet (Auchusa sempervirens) - - 220 Comfrey (Symphytum officinale) 222 Field Scabious (Knautia arvensis) 224 Mouse- Ear Hawkweed (Hieracium Pilosella) 226 Hemp Agrimony (Hupatorium cannabinum) - 228 Corn Sow-Thistle (Sonchus arvensis) 230 Transverse Section of Stem of Bracken Fern - 235 Cow-Parsnip (Heracleum Sphondylium) 238 Chicory (Chichorium Intybus) - - 240 Tutsan (Hypericum Androsemum) - 243 Garlic-Mustard (Alliaria officinalis) - 244 Water-Avens (Geum rivale) 246 White Bryony (Bryonia dioica) 251 Wall Pennywort (Cotyledon Umbilicus-Veneris) 252 Common Speedwell ( Veronica officinalis) 254 Creeping Cinquefoil (Potentilla reptans); Field Chickweed (Cerastium arvense) 256 Silverweed (Potentilla anserina) 259 Self-Heal (Prunella vulgaris) 262 Sea-Purslane (Arenaria peploides) 268 Butter-Bur (Petastites vulgaris) 272 English Stonecrop (Sedum anglicum) 275 Greater Plantain (Plantago major) - - 278 Dog-Rose (Rose canina) 280 Common Vetch (Vicia sativa) 283 Woodruff (Asperula odorata) 284 Round-Leaved Sundew (Drosera rotundifolia) 286 Common Butterwort (Pinguicula vulgaris) 289 Toothwort (Lathrea squamaria) - 292 Bishop-Weed (Aigopodinum. Podagraria) - 296

House-Leek (Sempervivum tectorum) 299

LIST OF FULL-PAGE PLATES xl

PLATR TO FACE PAGE

LVI. Ground-Ivy (Nepeta Glechoma) - - - 302 LVII. Marsh Gentian (Gentiana pneumonanthe) - 305 LVIII. Hemlock (Conium maculatum) - - - 308 LIX. Sea-Plantain (Plantago maritima); Buckshorn Plantain (P. coronopus); Ribwort Plantain (P. lanceolata) 312 LX. Rock-Rose (Helianthemum vulgare) 314 LXI. Meadow Crane’s-Bill (Geranium pratense) 316 LXII. Grass of Parnassus (Parnassia palustris) 318 LXIII. Cross-Leaved Heath (Frica tetralixz), Fine-Leaved Heath (B. cinerea), Ling (Calluna vulgaris) 321 LXIV. Early Purple Orchis (Orchis mascula) 322 LXV. Viper’s Bugloss (Hchium vulgare) 328 *LXVI. Herb-Robert (Geranium Robertianum) 331 LXVII. Hemlock Stork’s-Bill (Hrodiwm cicutarium) 332 *LXVIII. Meadow-Sweet (Spirea ulmaria) - 334 LXIX. Marsh Woundwort (Stachys palustris) 337 LXX. Scotch or Burnet-Rose (Rosa spinosissima) 344 LXXI. Yellow Archangel (Lamium Galeobdolon) 347 LXXII. Sea-Holly (Eryngium maritimum) - 350 LXXIII. Yellow-Horned Poppy (Glaucium luteum) 352 LXXIV. Bog-Bean (Menyanthes trifoliata) - - 360

There are in addition Highty Figures in the Tect.

CHAPTER I INTRODUCTORY—ASEXUAL PLANTS

In the beginning—Protopiasm. This wonderful substance, which Huxley has aptly called “the physical basis of life,’ received its name at the hand of Mohl of Tiibingen in 1846. The term is derived from two Greek words—prétos, first; plasma, form. Protoplasm is a slimy, gelatinous substance, of uncertain chemical constitution, fundamental to the existence of both plants and animals. It is known to contain carbon, nitrogen, oxygen, hydrogen, and some sulphates and phosphates of magnesium, potassium, and calcium; but no chemist has combined these constituents in such a way as to form living protoplasm. Besides the chemical components, the chemist has to reckon with the great factor Life—and Life is distinctly elusive. We have to bear in mind that the chemist in analyzing protoplasm must necessarily kill it in the process; he analyzes a corpse, from which the chief glory, Life, has been dismissed. Even supposing that the constituents of dead protoplasm may be combined in the laboratory in such a way that living protoplasm results, are we to conclude that Life has been created, that it would be a laboratory product ? Such a conclusion is by no means inevitable, 1 for may not the chemist have merely provided a combination of dead substances into which Life can enter, and through which it may manifest itself? Again, if it be claimed that the living product is due to chemical affinity, we naturally ask what this affinity is, and might reasonably conclude that it is an activity of Life itself. Perhaps it would be wiser to declare: In the beginning— Life; that Life is infinite, uncreate, without beginning, without end; that in Life nebule, suns, planets, plants, animals, and men “ live, move, and have their being ”’; that this same Life, into whose Holiest Place we may not enter, is at the back of all physical energy and chemical affinity; that it manifests its activity not only within the limits of what we call living matter, but also in the combinations of the elements, the motions of the heavenly bodies, and all the phenomena of the inorganic world. One does not venture to dogmatize upon these profound problems, but one likes to think that it is not dead force, but living activity, that is engaged in forming the tangible from the intangible, in framing solid solar systems from meteoric particles or gaseous nebule. Chemical affinity, one might aver, never produced Life, but, on the reverse, one might say that chemical affinity is a phenomenon of Life. In the strict sense in which the biologist regards Life, he declares that protoplasm is its physical basis; but one is not always disposed to accept biological limitations, nor to confine the notion of Life to plants and animals alone. The imperialist claims to think imperially, but the philosopher aims to think universally, and so the latter chafes at the notion of a particular substance being the sole basis of Life. Thinking universally, he asks, May not matter in its

THE ADVENT OF PROTOPLASM 3 entirety be the physical basis of Life? Let this question be granted, it would then appear that the wonderful protoplasm, in its first appearing on this earth of ours so many ons ago, was a newly-formed organic life-form, a mode of the Life which hitherto, for excellent reasons, had been able to manifest itself only in activities associated entirely with the inorganic realm.

One thing is certain, there was a time in the history of the earth when no plant or animal could exist, when protoplasm, which is fundamental to their existence, had not appeared. And a time arrived when, as one might say, at the psychological moment, lo! protoplasm came into being. Certain conditions were assuredly necessary for its momentous appearance. The earth’s crust would have to be sufficiently cool to allow of the condensation of water vapour into water, for water must have been the first abode of protoplasm and the first plants and animals. The chemical constituents necessary to the formation of the living substance must have been in solution in the water, and temperature and other factors, which, perhaps, elude the most scientific imagination, must have established a holy alliance in order that a stupendous and startling incarnation and virgin birth might result. And they are wise men, indeed, whose minds hark back with seemly reverence to the most momentous event in the physical history of the world— the advent of protoplasm.

Professor Schafer, in his much discussed Presidential Address to the British Association for the Advancement of Science, assembled at Dundee in 1912, asked whether we are justified in assuming that only at a remote period in the history of the world, and as it were by a fortuitous concomitation of substance and circumstance, living matter, presumably protoplasm, became evolved. He suggested that ancient conditions for the appearing of protoplasm were no more favourable than those which are at present in existence, and he was not sure but that its evolution might not still be taking place. These suggestions seem reasonable, and are the articulate expression of a feeling which must exist with many who are exercised about the origins of things. What has happened may surely happen again when the conditions are favourable. It seems more reasonable to think that protoplasm is still being evolved rather than that all that which now is has been derived from a modicum which evolved eons ago.

Our speculations are attractive, but we must come down to facts. The fundamental fact in plant and animal life is protoplasm, and a further fact is that it has been differentiated, from a period most remote, into plant and animal forms. Into the mysterious forces which led to such differentiation we shall not venture to inquire; we shall simply take facts as we find them. And one outstanding fact in relation to the simplest life-forms is the difficulty of deciding which is plant and which is animal. The old idea that plants are stationary and animals move does not hold good as a means of distinguishing between the two great kingdoms of nature; for there are undoubted plants which swim actively, and the living protoplasts in a tree as stationary as an oak certainly move within the narrow confines of their cell walls. Moreover, there are animals which are sedentary—for example, the sponges, which

AMG@BA PROTEUS 5 take up a fixed position from which they do not move. The nature of the problem before us will, however, be better appreciated if we make a study of some of the lower organisms.

In Fig. 1 we have a drawing which represents that remarkable organism known as Ameba proteus as seen under a fairly high power of the microscope. Specimens may be found on the surface of mud on the bottom of fresh-water ponds or pools.

To the naked eye they are mere specks, for they are seldom more than }, inch in diameter. We place a drop of water containing one or more of these specks on a glass slip, and, having covered the drop with a thin cover - glass, proceed to microscopic examination.

At first we experience some difficulty in locating our interesting subj ect, because, ee ee owing to the disturbance of c.v., Contractile vacuole; n, nucleus. the even tenor of its way, it is quiescent and hardly distinguishable among the fine particles of débris scattered in the thin film of water. Ina short time, however, we shall observe signs of movement, and be able to note several interesting details. Ameba is a speck of protoplasm of no definite form, yet capable of assuming many forms, in which respect it is thoroughly protean and altogether worthy of its specific name. Under a magnification of, say, 250 diameters, the main substance of this organism—that is, the endoplasm— is seen to be granulated with tiny particles of solid matter, while the ectoplasm, the outer surface or rind, is devoid of granules, and evidently firmer and less fluid than the granular endoplasm; yet it is highly elastic, as the movements of the organism show. And concerning these movements. They consist mainly in the formation of pseudopodia, or false feet. Portions of the body-substance are extended to form lobes or processes, as shown in the figure. These are the pseudopodia, the extension of which enables the Ameba to slowly change its position. It is calculated it can thus creep a distance of .j, inch in about an hour. Another movement, within the body, is the repeated formation and disappearance of a clear globule known as the “contractile vacuole.” This curious movement is due to the gradual accumulation at a particular point in the body of a drop of water which, having attained its maximum, is speedily discharged. We may assume that the function of the contractile vacuole is excretory. A third movement is that involved in feeding. The Ameba comes across some delectable morsel of organic food, such as a diatom, and proceeds to make a meal of it. Pseudopodia are extemporized as a means of grasping the food; in due course they reach round it, retract, and the food particle is now enclosed in a food vacuole in the substance of the organism. There, in that species of stomach made-to-order, the food is acted upon by a digestive ferment and so dispatched.

A point of exceptional interest in the constitution of the Ameba is the nucleus. This is a little round body in the endoplasm, of a somewhat mottled appearance.

AM@BA PROTEUS i:

It is not easily made out under ordinary conditions, but if the organism be killed and stained with iodine, the nucleus is stained a deeper brown than the rest of the protoplasm, and thus becomes easily apparent. Now we must consider the nucleus with some degree of reverential awe, for it is the vital centre, that structure through which Life itself regulates the existence and activities of a cell; it is the very heart of an organism, and even more. When an Ameba reaches its maximum growth it divides into two, a process of reproduction known as “fission.” But in this division the nucleus is always first divided; indeed, it regulates the division. If an Ameba be cut in two, and a part of the nucleus be included in each half, then each half will develop into a perfect individual; but if, in making the cut, the nucleus is not divided, then the part containing it will become a perfect individual, but the other part, although it may live for a few days, and even send out pseudopodia, cannot creep, nor can it digest food, although it may enclose it.

What, then, are our conclusions in regard to Ameba ? In the first place it is a cell, or protoplast, without a firm cell-wall. It can extemporize feet, and so move; it can capture food and digest it in an extemporized stomach; it can reproduce its kind by the simple method of fission; it is a speck of nucleated, living protoplasm displaying animal characteristics; it feeds upon organic food, such as microscopic plants; it cannot live in the absence of such food; it is an animal, like all other animals, utterly dependent, so far as food is concerned, upon other organisms, for it cannot live on inorganic substances. Before animals, no matter how small or lowly, could exist, it was essential that other organisms capable of feeding and thriving upon inorganic substances should make their existence practicable. Such organisms, as the sequel will show, are plants.

So we have no difficulty in deciding to which category Ameba belongs; it is certainly an animal. But we can come to no easy or certain conclusion with regard to those curious organisms commonly known as “ Slime- Fungi,” and technically designated Myxomycrtss (Gr. myra, mucus; mykés, a fungus), or Mycetozoa (Gr. mykés, and zdon, an animal). Over 400 species of Myxomycetes have been described; they occur on rotting leaves, wood, tan, etc., in damp situations; but although they are common, they do not seem to be known by persons other than naturalists. Yet they are of profound interest, for in no other organisms have we the opportunity of studying protoplasm without the limitations of cell-walls in such great mass. One species, Fuligo varians, or “ Flowers of Tan,”’ is frequently seen in summer on damp tan-bark; it is of creamy consistence, bright yellow in colour, and often extends to a breadth of about a foot. Thus seen, Fulgo is in its vegetative state, occurring as a mass of naked protoplasm; later, it passes into the reproductive stage. The life-history of a Myxomycete is very simple: the mass of naked protoplasm, called a “ plasmodium ”’ (plasm, a mould, or matrix), creeps slowly on the surface, say, of decaying wood, feeding and growing the while. In due course the organism ceases to feed, and a startling change takes place, for the plasmodium is converted either into a single fruit (sporangium) or a number of sporangia, in which a mass of

THE SLIME-FUNGI 2 dustlike spores are formed. These spores are ultimately liberated, and, being very light, are distributed by even the slightest currents of air; reaching a suitable substratum, they germinate into active swarm-spores, which either swim in water, with the assistance of lash-like processes, called “ flagella,’ or creep over damp surfaces of dead leaves, etc. These swarm-spores feed, grow, and repeatedly divide; finally, they coalesce, to form a plasmodium. Thus, the life-cycle is from plas-

Fic. 2.—BADHAMIA UTRICULARIS, PLASMODIUM, DRAWN FROM A STAINED SPECIMEN PREPARED BY Mr. A. LISTER.

a, a, Advancing margin. x about 5.

modia to spore-production. The spores develop into swarm-spores, and the latter settle down into plasmodia.

In Fig. 2 we have a drawing of a small plasmodium of the Myxomycete, Badhamia utricularis, which is often found on decaying wood, and even on the rotten timbers of old garden-seats. It should be sought in damp weather. It occurs in deep-yellow, slimy, flat, irregularly formed masses, feeding on species of fungi growing on the rotten wood. As the drawing indicates, thick veins of protoplasm traverse the mass, forming a species of network within which the living substance is in very 2 active movement. Microscopic examination reveals the fact that the plasmodium, as in all Myxomycetes, con-

Fic. 3.— BapHaMIA UTRICU- LARIS ; PoRTION oF Puas- MODIUM, x 1200, sHOWING SPHERICAL NUCLEI.

tains a great number of nuclei (p. 6), which are shown in Fig. 3. These nuclei increase by fission, and regulate the growth of the plasmodium.

No part of the mass is in the slightest degree cellular. If we will, we may see the organism feed. We place a portion of the fungus which the Myxomycete relishes in front of the creeping margin of the plasmodium, which soon flows over the food, engulfs it, and digests it in food vacuoles, after the manner of an Amceba; indigestible portions—the “bones,” as it were—are disgorged. The active plasmodium creeps in the direction of moisture, and avoids strong light; but when it is ready for spore-formation, it creeps away from a damp substratum to the driest location it can find, and also courts strong light. In a period of drought, the plasmodium, probably for self-preservation, may cease its activity, divide into a number of parts, each part containing a number

Fic. 4.— Comatricna OBTUSATA.

a, Group of sporangia, natural size; b,empty sporangium, x 16, of nuclei, and forming a cell-wall of hardened protoplasm. This process is called “ encystment,” each cell being a cyst, and the mass of cells is named a “ sclerotium ”

THE SLIME-FUNGI It

(Gr. skleros, hard). In this form a Myxomycete may live for some years. When a sclerotium is damped, the walls of the cysts are softened, and the organism resumes its plasmodial form and activities. Fig. 4 shows a group of the fruits, or sporangia, of the species Comatricha obtusata, as well as an empty sporangium. The spores which are formed in these vessels are quite dry when they are exposed for distribution, and in a dry

DIFFORME. Swarm-CELLS ASSEMBLING AND

a, Spore; b, swarm-cell emerging COALESCING TO FORM A PULASfrom envelope; c, swarm-cell MODIUM.

newly hatched; d, swarm-cell §m, An encysted swarm-cell; v., enwith flagellum ; e, swarm-cell cysted swarm-cell being digested with bacteria in food vacuoles; in a vacuole; s, empty spare f, swarm-cell in amceboid form, envelope.

condition they retain their vitality for an indefinite time. They can germinate only in moisture. The formation and appearance of the swarm-spores is shown in Fig. 5. The swarm-spores swim with what is described as a “‘ dancing movement’; they can digest solid food; they increase by fission, and in a time of drought may become encysted. As already stated, the swarm-spores ultimately coalesce, to form a plasmodium; but before this occurs, they lose their flagella, ceasing to swim, and contenting themselves with creeping movements of an amoeboid type. The assembling and coalescence into a plasmodium is illustrated in Fig. 6.

From this brief sketch of the life of the Myxomycetes we see that in their plasmodial forms, and as regards their swarm-spores, they can digest solid food after the fashion of Amebe, and in this and other respects display distinct animal characteristics. Moreover, they are dependent upon organic material for nutrition, as is the case with all animals. At the same time we know that there are undoubted plants, such as the fungi and bacteria, which, unlike green plants, do not build up inorganic material into organic form, but depend upon organic material in nutrition. But these plants absorb food in solution through their cell-walls, and do not eat solid material. But in the matter of spore-formation and reproduction, the so-called ‘‘ Slime Fungi” display some likeness to fungi and therefore we need not wonder that in the past they have been claimed as animals by zoologists, and as plants by botanists. The modern attitude towards them is that of discreet agnosticism, and there is a distinct inclination to relegate them to a position in the genealogical tree of Nature peculiarly their own.

The Bacrerta, which we propose to consider briefly, are classed as plants. Popularly known as “‘ microbes,”’ they are regarded with horror by a public which associates them entirely with disease. True it is that bacterial organisms have an intimate connection with such

THE BACTERIA 13 diseases as anthrax, cholera, diphtheria, leprosy, tuberculosis, and others; but we ought not to hastily condemn all Bacteria as workers of evil because some of them are associated with disease. As a matter of fact, we should be in a very bad case indeed were it not for the beneficent activities of hosts of these exceedingly minute plants, and it is reassuring to know that some forms which are parasitic in the human body are practically harmless. This is the case with a number of forms which live on the mucous membrane of the mouth, and a particular species, Sarcina ventricult, found in groups, or packets, in the alimentary canal. Bacteria, in general, are either parasites, in which case they live at the expense of living plants or animals, or saprophytes (Gr. sapros, rotten; phyton, a plant) feeding upon dead and decaying organic matter; and the saprophytic forms have an exceedingly important place in the economy of Nature, for they are the chief agents in breaking up dead plant and animal bodies, and rendering their substances fit for absorption by higher plants. Without the good offices of Bacteria, the higher plants would certainly suffer, and we know that animals and men could not exist without the ministrations of the plants. Then there are Bacteria which are actually able to fix free nitrogen from the atmosphere and make it available for the food of plants with which the organisms are associated. Such Bacteria occur in tubercles on the roots of plants of the Pea order; they seem to provide the host-plants with nitrogen, which is essential to the existence of protoplasm, in exchange for bed and board. Thus, it happens that many plants of the Pea order (leguminous plants), being infected with nitrogen-fixing Bacteria, enrich the soil in which they grow, and it is not uncommon for agriculturists to plough in crops of leguminous plants in order to increase the fertility of the soil. The fact that Bacteria are agents in the purification of sewage should also be placed to their credit.

Bacteria are practically ubiquitous. If we ascend the hills, they are there, for they have certainly been recorded at an altitude of 10,000 feet. They abound in soil and water, even in the water we drink, which, by the way, would be decidedly “ wersh”’ without their presence. They also float about in the air, and are distributed amongst the dust which we raise with our feet as we walk. When we inhale the fragrance of flowers, we may draw Bacteria from the petals into our nostrils. When we kiss, we may “ exchange microbes.” When we stroke a dog, we may scatter a host of these organisms. It has been calculated that no less than 50,000,000 of Bacteria may be contained in so little as an ounce of roadside dust. Their size is so exceedingly small that in the case of such a germ as that of the Bubonic Plague 250,000,000 would cover about a square inch of soil, and be able to thrive on it. The average short diameter of the Bacteria is said to be about zsdou Inch. These organisms are not easily killed; they can survive great extremes of temperature. In an experiment a number (forty-four) were exposed to the intensely cold temperature of — 210° C., yet were able to survive. Dry spores resist high temperatures; they have survived a ten minutes’ exposure to 150° C. Nor need we think that mere boiling will kill certain spores, for some are known to be able to survive even after being boiled at a temperature of 100° C. for several hours.

THE BACTERIA 15

The Bacteria are the smallest known plants, and when we consider the infinitesimal result of the activity of a single individual, and yet grasp the enormous effects of the activity of Bacteria in the aggregate, the pessimists among us, given to minimizing the importance of the human unit, may well take heart of grace. But while these organisms teach us the value of the unit, we shall have no desire to emulate them in the matter of multiplication. It is calculated that a single microbe, under very favourable conditions, may have millions of descendants in a few hours! The bacterial population of 4 cubic inch of cream standing about forty hours may reach to 500,000,000! Most Bacteria love darkness rather than light, and are killed by direct sunlight in a few hours; they can stand diffused light much longer. But some species of the Purple Bacteria—able to feed on sulphide of hydrogen—thrive well in light, and are attracted by it.

Some authors consider Bacteria to form a distinct group of Fungi; they certainly display fungal characters; but perhaps it is premature to declare definitely that they are Fungi, for we have yet much to learn about them. They may be described as very minute one-cell plants of the simplest structure, of a parasitic or saprophytic nature, some of them capable of active movements, and all, without exception, multiplying by transverse division or fission; they may also produce resting-spores or -cells. They vary in form, and for convenience in description are commonly classed as:—