Agricultural botany, theoretical and practical

Front matter

G ill in

22102088067

Med

Part I. General External Morphology

CHAPTEK

I. Introductor V ......

II. Seeds: their structure am* germination

The common bean, 7 ; White mustard, 16 ; Onion. 19 : Wheat, 22.

III. The root ......

Primary and secondary roots, 25 : Adventitious roots, 28 ; Root-hairs, 32.

IV. The vegetative shoot: stems, leaves and buds

Buds, 37; Branching of stems, 40: Twigs of trees in winter, 42 ; Spurs, 44 : Dormant buds. 50 ; Adventitious buds, 51 ; Stems and their varieties, 52; Recognition of trees by means of twigs in winter, 6t.

V. The leak. ......

Foliage-leaf, 68; Modified leaves, 72; Leaf-arrangement. 74; Bud-arrangement, 76 ; Leaf-fall; Evergreens, 76.

VI. The flower ......

Arrangement, symmetry and number of tioral leaves, 80 ; The receptacle, 81; Non-essential parts of the flower; perianth, 83; The Calyx, 83 ; The Corolla, 83 ; The essential parts of the flower, 83; The Androecium, 84; The Gyntecium, 85; ITacentation, 87; Monocltnous and diclinous flow ers ; monoecious and dioecious plants, 87.

VII. The inflorescence .....

Racemose inflorescences, 89; C'ymose inflorescences, 92; Mixed inflorescences, 93.

VIII. The fruit: Dispersal of seeds

Indehiscent dry fruits, 96 ; Schizocarps, 97 ; Dehiscent dry fruits, 97 ; Succulent or fleshy fruits, 99 ; Dispersal of seeds, 100.

PACE

1-6

VII

VI 11

CONTENTS

Part II. Internal Morphology Anatomy)

CHAPTER

IX. Thf. plant cell: Cell-division: Tissues .

The cell, 105: Cell-division; Continuity of protoplasm, 110; Tissues, hi.

X. The anatomy of the stem, root and leaf

The herbaceous stems of dicotyledons, 113 ; The perennial woody stems of dicotyledons, 122; Stems of monocotyledons. 136; The root, 140; The green foliage-leaf, 144; 'I'he growing-points of stems and roots, 148,

Part III. Physiology Of Plants

XI. The chemical composition of plants

Carbohydrates, 155; Fats and fixed oils, 163; Volatile or essential oils, 163 ; Organic acids, 164 ; Proteids or Albuminoids, 165 ; Amides, 166 ; Alkaloids, 166.

XII. The composition of plants ( continued 0

The elementary constituents of plants, 167 ; Water-culture, 168 ; Essential elementary constituents of plants, 170; Non-essential elementary constituents, 174.

XIII. Osmosis; absorption of water .

Osmosis, 176; Absorption of water, 181 ; Root pressure ; 'bleeding ’ of plants, 185.

XIV. Transpiration .....

Transpiration, 190 ; Transpiration-current, 197.

XV. The absorption of food-materials

Food and food-materials, 200 ; Food-materials and their absorption, 201.

XVI. ‘Carbon-fixation,’ ‘Assimilation’ or ‘Photosynthesis’ . .

I’ ACtE 104

'>3

‘52 16 7

CHAI'TER

XVII. Formation of proteids. Translocation and

STORAGE OK FOODS ....

Formation of proteids, 216 ; Utilisation, translocation and storage of plant-foods, 218; Nutrition of semi-parasites and semi-saprophytes, 224.

XVIII. Enzymes and the digestion of reserve-materials .....

XIX. Respiration .

Ordinary respiration, 232; Intramolecular respiration, 237.

XX. Growth ......

Growth. 239; Conditions which influence growth, 242 ; spontaneous movements of grow th ; nutation anti tissue-tension, 246 ; induced movements of growth, 249.

XXI. Reproduction .....

Vegetative reproduction, 257; Cuttings. 258; Layers, 260; Budding and grafting, 261,

XXII. Reproduction (continued) ....

Sexual reproduction. 268 ; Structure and germination of the pollen-grain, 268; The o\ule and its structure. 270; Fertilisation and its effects, 272 ; Pollination ; Self-fertilisation and Cross-fertilisation, 278; Transference of pollen. 280; Sexual affinity: hybridisation and hybrids, 284 ; Artificial pollination ; methods of crossing, 288.

XXIII. Cultivated plants and their origin; Plant breeding .....

Bud-varieties or ‘sports,’ 293: Variation among seedlings, 294; \ ariations, how induced, 301 ; Correlated variability, 305 ; Reversion, throwing Ixtck or atavism ; Degeneration of varieties, 306.

Part IV. Classification And Special Botany Of Farm Crops

XXIV. The classification of plants

Individual and species; variety and race, 310; Genus; plant-names, 310; Divisions of the Vegetable Kingdom, 312.

X

CONTENTS

CHAPTER

XXV. Cannabacete ......

The Japanese Hop, 321 ; The common Hop, 321 ; Hemp, 337.

XXVI. CHENOPODIACE/K .....

Sea Beet, 340; Common Beet, 340 ; Mangel wurzel, 341 ; Sugar-

XXVII. CrUCIKKR.'K .

Wild cabbage, 354 ; Cultivated cabbage and its varieties, 35s ;

Turnip, 359; Swede, 364; Rape, cole or coleseed, 367; Black mustard, 369 ; White mustard, 371 ; Charlock, 373; Wild Radish,

XXVIII. ROSACE/E • 377

Plums and;Cherries, 377 ; Sloe, Bullace, Wild Plum and Apricot,

379; Dwarf Cherry, Gean, Bird Cherry, Almond, Peach, 380; Strawberries, 381 ; Raspberry and Blackberry, 383 ; Dog Rose, 384 ;

Pear, 385 ; Apple, 386 ; Medlar. Whitethorn and Quince, 387 ;

Lesser Burnet, 388.

XXIX. Leguminoste ...••• 39°

Peas, 392; Bean, 396; Vetch, 398 ; Vetchling, 400 ;] Red clover,

401 ; Zig-zag clover, 404 ; Alsike, 405 ; V hite clover, 405 ; Crimson clover, 406 ; Yellow suckling, 408 ; Hop clover, 408 ; Black medick,

409 ; Lucerne, 409 ; Melilot, 412 ; Sainfoin, 412 • Serradella, 4 1 4 ,

Kidney Vetch, 514; Bird’s-foot trefoil, 415; Gorsc, 416; Rest- Harrow, 417 ; Lupins, 4T7.

XXX. UM BELLI FER7E . • • • . 42 1

Wild carrot, 424 ; Cultivated carrot, 424 ; Parsnip, 432 ; Hemlock,

434 ; Water Hemlock or Cowbane, 434 ; Water Dropwort. 435 ;

Fool’s Parsley, 435-

XXXI. Sola yaceze . . • • • 436

Potato, 436 ; Bitter-Sweet, 448 ; Black nightshade, 448 ; Deadly nightshade, 448 ; Henbane, 449.

XXXII. Composite ...••• 45°

General characters of the Order. 45°; Yarrow; Millefoil or Thousand-leaf, 453.

XXXIII. Graminete. True Grasses . • -455

XXXIV. Graminkte ( continued ). Cereals . • 463

XXXV. Cultivated and Wild Oats (Genus Avena) 473

Wild Oat, 473: Bristle-pointed Oat, 474; Animated or Ply Oat,

474; Short Oat, 474; Common Cultivated Oats, 474-

CONTENTS xi

CHAPTER PAGE

XXXVI. Cultivated Barleys (Genus Hordeum) 481

Cultivated Barleys. 482 ; Distinguishing features of Barley-grains,

487 ; Characters of a good malting barley, 489.

XXXVII. Cultivated Rye (Genus Secale) . 495

XXXVIII. Cultivated Wheats (Genus Trituum) 496

XXXIX. Common Grasses of the Farm 510

XL. Grasses and Clovers for temporary and

PERMANENT PASTURES . . 536

Grasses and clovers for leys of one, two or three years’ duration, 538 ; Grasses and clovers for temporary pastures lasting from three to six years ; Grasses and clovers for permanent pasture, 541; Weight of seed to l>e used, 546.

Part V. Weeds Of The Farm

XLI. Weeds: General . . . . 551

Their injurious effects, 551; Duration of weeds, 559; Habit of growth of weeds, 561 ; How weeds are spread, 563 ; Extermination of weeds, 564.

XLI I. Weeds: Special ..... 572

Weeds of arable ground, 572 ; Weeds of pastures. 584.

Part VI. Farm Seeds

XLI II. Farm Seeds: General .... 593

Purity, 595; Germination Capacity, 599; Speed of germination or germination energy, 605 ; Weight, 608 ; Form, colour, brightness and smell, 614.

XLIV. Farm Seeds: Special

Xll

CONTENTS

Part VII

FUNGI, CONSIDERED CHIEFLY IN RELATION TO SOME COMMON DISEASES OF PLANTS.

CHAPTER PAGE

XLV. Fungi: General ..... 655

Hypha and mycelium, 655 ; Reproduction, 657 ; Germination of spores, 660 ; Mode of Life ; saprophytes and parasites, 661 ; General advice to be followed when dealing with plant diseases, 664.

XLVI. Fungi {continued) Phycomycetes . 666

Eumycetes, 666 ; Phycomycetes (sub class i. Zygomycetes), 667.

XLVI I. Fungi {continued) Phycomycetes . . 670

Phycomycetes (sub-class ii. Oomvcetes), 670 ; Damping-off, 671 ;

Potato diseases, 675.

XLVI II. Fungi {continued) Basidiomycetes . 691

' Smut ’ of Oats, 692 ; ' Smuts ' of wheat and barley, 695 ; Bunt of wheat, 699 ; Rust and mildew of wheat, 702 ; Other species of Rusts,

711 ; The common mushroom, 716.

XLIX. Fungi ( continued ) Ascomycetes . . 721

Yeasts, 722 ; Mildews, 724 ; Ergot, 734.

L. ‘ Club-root’ Disease .... 739

Part VIII. Bacteria

LI. Bacteria : their morphology and reproduction .... . • 745

Eornts of Bacteria, 745 ; Vegetative reproduction, 746 ; Reproduction by means of spores, 747 ; Conditions affecting development,

750 ; Sterilisation and pasteurisation, 752.

LI I. Bacteria: their work . . . -755

Lactic fermentations, 756 ; Butyric fermentations, 758 ; Acetic fermentations, 759 ; Fermentation of cellulose, 760 ; Fermentation of urea, 761 ; Putrefaction, 762; Nitrification, 764: Denitrification,

767 ; Fixation of free nitrogen, 768 ; Bacteria and diseases of animals, 776.

Chapter I. Introductory

i. The things met with every day can be separated into two distinct classes or groups, namely, those which are alive, such as birds, insects, cattle, trees, flowers, and grasses, and those which are never possessed of life, such as air, water, glass, and iron.

Although it is impossible to give a complete and satisfactory account of what life is, for all practical purposes the difference between the two classes of objects is easily recognised, and a more extended study of them leads to the conclusion that between the living and the inanimate world there is a hard and fast line of separation.

The chief and most obvious peculiarity of living things is their power of giving rise to new individuals— that is, their power of reproduction. They are ordinarily separated into two classes, namely animals and p/ants. The term Biology in its widtfSt sense is used to denote the study of all forms of living things, that branch of it dealing with animals being known as Zoology, while the science of Botany is concerned with the study of plants. The most familiar animals have the power of moving about in | a waY which is not possessed by plants. Moreover, the former I require as food, substances which have been derived from other ■ living things, such as flesh of all kinds, milk, bread, potatoes,

| and similar materials ; while most common plants are capable of utilising substances which belong entirely to the inanimate world, such as carbon dioxide, water, and various minerals. Although these points of difference between plants and animals are sufficient to separate the two classes from each other, so far as the purposes of everyday life are concerned, it must be mentioned that a further examination of living things shows that there are some which in structure and power of utilising inorganic substances as food-materials resemble plants, but which are nevertheless able to move about as freely as animals, and that other structures usually considered as animals move very little. Then, again, there are living things always classed as plants, which produce flowers and seeds, although they cannot live when supplied with carbon dioxide, water and minerals, but must be fed upon the same or similar substances to those needed by animals. Indeed, all attempts to draw a hard line of separation between plants and animals are found to end in failure. The living substance within them appears to be the same, and between the so-called animal and vegetable kingdoms there is no distinct point of difference. The living world is essentially one, and not two, and it is very necessary to constantly bear in mind that plants are just as much living structures as animals are, since by far the larger number of mistakes in the management and cultivation of plants are due to want of proper appreciation of this fact.

2. For the present our attention will be confined to the common plants of the farm and garden. In form and structure these are altogether different from animals, and as the difficulty of defining the two classes of living things is only met with in studying minute and practically unseen organisms it may be dismissed for the present.

It will be readily understood that plants may be studied from a great many different points of view, and consequently special branches or divisions of the science arise. Attention may be confined to an investigation of the uses of the various parts of a plant’s body — to the work which the leaves, roots, and flowers perform in the life of the plant ; this part of the subject is known as physiology. Another branch is concerned with the form, origin, development, and relationship of the various parts to each other, without any reference to the work they do : the term morphology is used to denote this division of the science.

Then, again, the structure and arrangement of the various parts of plants may be studied in order to determine their points of similarity and of difference with a view of placing together in groups all those possessing certain degrees of resemblance : this is usually termed Systematic Botany. For purposes of convenience and methodical extension of knowledge of the subject many other divisions of the Science are made, and in each of them the study of plants is made from a somewhat different standpoint. Although other classes of the vegetable kingdom need attention it is advisable to confine our study at first to the seed-bearing plants, as this division includes all those which are everywhere most familiar. It is essential that farmers and all who are interested in the management of plants for pleasure or profit should examine and investigate them from as many different aspects as possible, as only by so doing can real progress be made in their cultivation.

3. Most plants of the farm belong to the class known as Spermaphytes or seed-bearing plants; the latter are sometimes called Flowering plants or Phanerogams, but their chief characteristic is the production of seeds. The life-history of a spermaphyte is a continuous process of development or unfolding of parts in which we may recognise four fairly distinct periods, namely

(1) Germination of the seed and the escape of a young plant

from it ;

(2) The development and growth of roots, stems, and green

leaves ;

(3) The flowering period or formation and opening of flowers :

and

(4) The production and ripening of fruits with their contained

seeds.

The succession of events is generally in this order, and usually the formation and unfolding of roots, stems, and leaves occupies by far the greatest portion of the plant’s life.

There is, however, great variation in the time taken to reach the several stages of development, and the periods are not always of the same duration in the same species of plant.

4. So far as their total duration of life is concerned, plants may be usefully divided into annuals , biennials , and perennials.

By an annual is meant a plant which completes its life-history in one growing season. Starting as a seed in spring or early summer, it develops root, stem, and leaves, and then produces flowers and seeds, after which it dies, leaving behind it offspring in the form of seeds. The time taken by annuals to reach the stage of seed-production is not always the same ; usually the whole of the season, from spring to autumn, is necessary, and only one generation is produced in that time. Some of them, however, termed ephemerals, such as chickweed and groundsel, produce seeds in a few weeks, and these may germinate and produce a second and third crop of plants before frost cuts them down in autumn and winter.

Biennials , beginning life as seedlings in spring or summer, occupy the first growing season in the production of root, stem, and leaves only. They then rest during winter, and in the following year start growth again, and produce a stem bearing flowers and seeds, after the ripening of which the plant dies. Wild carrot, parsnip, and some varieties of thistles behave in this manner.

Perennials are plants which live more than two years, and often several seasons elapse before flowers and seeds are produced. They are frequently divided into two classes, namely, (x) herbaceous perennials and (2) woody perennials. In the former the leaves and stems above ground are of a soft nature and die down at the end of the growing season, the parts of the plant which still remain to carry on growth in subsequent years being underground : the stinging nettle, hop, and potato are representatives of this class. In woody perennials, of which all trees and shrubs are examples, the stems above ground are hard and woody.

This method of dividing plants according to their length of life, although useful, is by no means a strict one, as the duration is dependent to some extent upon season, time of sowing, and the treatment which they receive. Wheat, for example, if sown in early spring behaves as an annual, but if sown in late summer or autumn does not perfect its seed and die until the following year. If kept continually cut or cropped down by animals it may even remain two years or more without dying, especially when thinly sown on good soils and allowed plenty of room for branching. Annual mignonette of gardens is often made to last several years in pots by pinching off the flowering stems as soon as they ! begin to form.

Turnips and other plants, usually biennials in ordinary farm practice, are invariably annuals if sown early in the year, say in February.

Climate and soil also influence the duration of plants, annuals in some districts becoming biennial or even perennial in others.

Ex. 1.— Sow short rows ol the cereals and ‘ roots ’—mangels, turnips, •swedes and carrots— on the first day of each month during a whole year, and make caretul observations and notes on their subsequent growth up to the time of seed production. Interesting and useful results are obtained.

5. As the duration of flowering plants is subject to such varia- | tion and their classification into annuals, biennials, and perenjrn.ia.ls, consequently somewhat arbitrary, they are sometimes ■ l^aced in groups according to the number of times they are able to produce seeds.

1 hose which yield only one crop and then die are termed monocarpic plants : annuals and biennials are of this nature, and some perennials also.

Such plants as most trees and shrubs, thistles, bind-weed, coltsfoot, and many grasses which are able to produce flowrers and seeds during an indefinite number of seasons are described as polycarpic.

Chapter II

iSEEDS : THEIR STRUCTURE AND GERMINATION.

ii. It is well known that one of the most ordinary methods of rraising plants is to sow what are called seeds, yet how few there jare among the many who use them who fully appreciate their rreal nature and capabilities. This want of knowledge is not due perhaps so much to want of interest in them, as to the fact that for their proper management they are usually buried away in the ^ground, and are therefore unseen ; moreover, many of them are so small that their structure is difficult to observe with the naked eye.

In order to understand the true nature of a seed it is necessary to examine its origin and construction, and watch its development as far as possible from the earliest stages to the time when it gives rise to a completely formed young plant.

The Common Bean. — A broad bean is one of the largest seeds met with in ordinary farm or garden practice, and as its parts are all sufficiently large to be observed without the special aid of anything more than •an ordinary pocket lens, it is especially fitted for study.

When a nearly ripe pod of a broad bean plant is opened, each seed within it is found attached to the inside by means of ,

r ig. i. — Piece of bean pod showing the funicle (/)

a short Stalk or funicle and its attached seed.

(Fig- l)> it is through this stalk that all the nourishment passes from the parent to enable the young seed to develop. At first the pod exists in a rudimentary form in the centre of a flower, and its parts and contents are very small j they are nevertheless readily seen with a pocket lens. After the fading of the flower, the pod and seeds within it grow larger and larger at the expense of food supplied by the rest of the plant, and ultimately when ripe the funicles wither and dry up, and the seeds become detached from the parent which has produced them.

When dry and ripe each bean seed is hard, with an uneven surface, but its internal construction cannot be clearly examined in this condition. On soaking in water for twelve hours, however, it becomes softer, and the parts can then be easily investigated.

The outside, which is a pale buff colour, is smooth, and has at one end a narrow elongated black scar called the hilum of the seed. It is known popularly as the ‘ eye ’ of the bean, and marks the place where the broad end of the funicle separated from the seed when it ripened in the pod.

Quite close to one end of the hilum is a very minute hole known as the micropyle, easily seen with a lens, and through which water oozes out usually accompanied by bubbles of air

when soaked beans are squeezed between the finger and thumb. This opening communicates with the interior of the seed, and is the only one it possesses.

On slitting round the edge with a knife, the outer part of the bean can be stripped off as a pale, semi-transparent, leathery membrane ; this is known as the testa or seed-coat, and is thickest

Fig. 2. — Bean embryo, showing (r) radicle and ( c ) cotyledon.

Fig. 3. — The same as Fig. 2, after removal of one cotyledon ; r radicle ; b the plumule ; c cotyledon of embryo.

THE COMMON BEAN

. and of softest texture where the hilum is situated. The rest of the seed after the testa is removed, is of oval flattened shape : similar to the complete bean, and is divisible into two large fleshy halves called cotyledom^xg. 3, c), which, however, are not 1 completely separate from each other, but connected at the side with a conical projecting body (Fig. 3, r), one end of which is found to fit into a hollow cavity in the seed-coat exactly opposite the micropyle ; the other end is bent and turned inwards between the fleshy cotyledons. The extent and shape of this small curved structure is most easily observed when one of the cotyledons is removed completely ; it remains attached to the other as in Fig. 3.

Ex. 2. — Soak some broad beans in water and keep them in a warm place all night. Examine them next day and make drawings of the various parts seen both before and after stripping off the testa. Observe the relative (position of the parts of the embryo in reference to each other and to the seed -coat.

Examine and compare the structure of the following seeds after soaking in : the same way : — Pea, scarlet runner beans, vetches, and red clover.

The bean seed contains nothing more than what has already been described ; the nature and relationship of its component parts only become intelligible when the seed is placed in the ground or maintained under certain conditions, and allowed to grow. When growth commences the lower end of the small curved structure (Fig. 3, r) elongates and breaks its way through the 1 coat of the seed at a point very close to the micropyle, but not, as often erroneously stated, through the micropyle itself. It soon assumes the form seen in Fig. 4, and is recognised as a root of a young bean plant. The upper bent half, which lies between the cotyledons, also pushes its way out of the same opening in the seed-coat and develops into a stem, from the tip of which leaves are gradually unfolded. It is thus seen that the seed of a broad bean is a packet containing a bean plant in a rudimentary condition.

1 his plantlet is called an embryo, and the portion of it which

IO SEEDS : STRUCTURE AND GERMINATION becomes root and stem is its primary axis. The part of the primary axis which is below the point where the cotyledons are attached is known as the radicle , and consists of a very small piece of stem, the hypocotyl , at the epd of which is a root. Where

the stem ends and the root begins cannot be determined in the bean seedling without the aid of the microscope and examination of the internal structure of the axis of the plant.

The curved end of the primary axis above the cotyledons is the plumule of the embryo, and consists of a very short piece of stem, the epicotyl , on the top of which is a bud. From the latter is derived the ordinary stem which comes above ground with its green leaves and flowers.

In the early stages of the

growth of the embryo from

the seed the hypocotyl grows

very little, the part of the

F” VCSSfctaKtSS £££ ?&£ stem which grows most being ‘'don; ^ primary root ; 6 ep.cotyl with ^ epicotyl It js on acc0unt

Compare with Fig. 3. Qf the elongation of this

portion of the plantlet that the plumule with its young leaves are driven above ground, the cotyledons remaining below enclosed within the seed-coat.

The upper part of the stem bearing the plumule comes out of the seed bent, as in Fig. 4, and it maintains this curved shape for

THE COMMON BEAN

1 1

■some time after emerging. By this behaviour the delicate leaves of the plumule are protected from injury during their [progress upwards when a seed is sown in earth or sand.

Ex. 3. — Fold up some soaked beans in two thicknesses of white flannel made damp, and place them on a plate. Cover them with another plate [placed upside down, and leave them in a warm room. Examine them twice ;i day, leaving them exposed to the fresh air for a few minutes each time,

. and keeping the flannel damp, not wet. When they sprout notice the place "where the radicle has coine out of the seed-coat. Let some grow till the ■radicle and plumule are well out of the seed, and compare the various parts of the sprouted seeds with unsprouted ones.

2. Germination. — When the pod of the bean is developing, the eembryo in the seed is being fed by the parent and visibly grows until ripeness is attained. The young plant then assumes a dor- I rnant or resting state within the seed without showing any signs 1 of life. Under certain conditions, however, the plantlet begins tto wake up, and soon escapes from its protective coat to lead aa separate and independent life. This awakening from a resting (•condition to a state of active growth is called germination, and ;is dependent upon an adequate supply of (i) water, (2) heat, and (3) air or oxygen. It is also essential, of course, that the I plantlet in the seed must be alive.

The exact nature of the dormant state of seeds is not

I understood, but in old seeds and those which are gathered in an immature condition or badly stored the embryo is often weakened or actually dead ; in the latter case no germination is possible. The exact length of time which seeds may be kept before death of the embryo takes place has never been satisfactorily determined ; it varies with the species of the seed, its ripeness and composition, and also with the | method of storage. In the case of most farm and garden seeds kept in the ordinary way, few of them are found capable of growth < after ten years, and a large number die in two or three years, but i on this point more will be said in a later chapter. For present purposes it will suffice merely to mention that age is a determining factor in the germination of seeds, apart from the three conditions previously mentioned.

3. That water is necessary is well known, as beans may be kept indefinitely in a sack or drawer at various temperatures and with access to air without germination taking place. W hen placed in moist ground, or between damp blotting-paper, they absorb water very readily. This is most easily observed when beans are soaked for twelve hours in a dish containing water. The water is transmitted through all parts of the coat, but much more quickly and easily through the micropyle and the line of softer material which runs the whole length of the centre of the lulum. It is rapidly brought into contact with the part of the embryo which grows first, namely, the radicle. The soft spongy thicker part of the inside of the testa lying beneath the hilum stores up a considerable amount of water for the benefit of the developing plant, and the whole of the embryo and the seed-coat absorb water and become softer and larger in consequence ; it is only after this swelling has happened that a bean begins to show any signs of germination.

Ex, 4. —To show the influence of the micropyle and hilum in the absorption of water, take twenty beans all as near the same size as possible. Paint over the micropyle and hilum of ten of them with quick-drying varnish or « cycle black ’ ; on the other ten paint streaks of the same size on the sides of the seeds, leaving the micropyle and hilum untouched. \\ eigh both ots separately, and place them together in a basin of water all night. Take them out next morning, dry them carefully with a towel, and weigh agam, and see which lot has increased most.

4 The need of an adequate temperature for germination is a matter of common knowledge among those accustomed to sow seeds. If soaked beans are placed in the ground in midwinter they show little or no signs of waking from their dormant condition, yet when placed under a glass on damp blotting-paper indoors, the radicle makes its exit from the seed in a few days. Seeds differ in the temperature which is necessary to induce them to germinate, the embryos in some commence to extend

THE COMMON BEAN

1 3 ttheir radicles and push their way through the seed-coat even if i just kept above freezing point; others require a temperature of • 9° or io° C. to start growth. If attempts are made to grow beans :at 450 C. it will be found to be too hot, and they make little or mo progress. Between this high temperature at which growth ^appears impossible, and the freezing point where the development of the embryo of the bean is also suspended, there is a Temperature at which the embryo makes the most rapid progress, sand emerges from the seed-coat in the shortest possible time ; This most favourable temperature is about 28° C., both above it and below it the germination of the bean is retarded.