Cornell University Library OF THE Rew Work State College of Agriculture di. £022. loMVLL7. 8101 Cornell University Library SB 107.P42 1910 i 3 1924 000 603 971 mann AGRICULTURAL BOTANY AGRICULTURAL BOTANY x THEORETICAL AND PRACTICAL BY JOHN PERCIVAL, M.A., F.L.S. PROFESSOR OF AGRICULTURAL BOTANY UNIVERSITY COLLEGE, READING FOURTH EDITION NEW YORK HENRY HOLT AND COMPANY 1g10 be All Rights Reserved PREPAGE PRACTICAL men and the agricultural press have from time to time complained of the absence of text-books of botany suited to the wants of the student of agriculture, those in existence being works which treat the subject from a purely scientific standpoint and contain a large amount of matter which, though important to the botanist, is nevertheless of little interest or value to the agriculturist whose time for training in such matters is necessarily limited. The recent growth of interest in technical instruction, which has resulted in a.large increase in the number of colleges and schools for agricultural education, has rendered it imperative that so serious a defect should be remedied, and this I have endeavoured to do by writing the present volume. The contents are based upon many years’ experience in teaching and lecturing to students, practical farmers and gardeners, and embrace all those botanical matters which such experience has led me to consider essential to a sound working knowledge of the general principles of the science and its more immediate application to the crops’of the farm. Although the book has been primarily written for the benefit of students of agriculture, the greater portion of it is equally well adapted to meet the requirements of gardeners and all who desire to obtain an insight into the general structure and life- processes of plants, a knowledge of which must undoubtedly conduce to a more satisfactory and economical management of all cultivated plants. Until quite recently ‘atatiteal knowledge has apparently been deemed of little importance in examinations in the science and practice of agriculture, the science of botany being usually tréated as an ‘optional subject.’ It is, how- ever, gratifying to note that in the new regulations for the examination for the National Diploma in the science and practice of Agriculture, issued by the National Agricultural Examination Board, Botany takes its proper place as an obligatory subject beside its sister science Chemistry. v vi PREFACE All the drawings in the work are original, and with the excep- tion of the diagrammatic figures have been made by the author from living or natural examples. The panicles or ‘ears’ of the grasses are all drawn the natural size of average specimens, in order that the figures may be of use in the identification of these important plants. The farm seeds are also drawn to a uniform scale; their rela- tive sizes may therefore be seen at a glance. In this as in all scientific study, practical work is absolutely essential to a proper understanding of the subject ; in recognition of the importance of such work I have introduced into the text of the volume a series of exercises and experiments, illustrative of the principles and facts to be studied. These and others, which will suggest themselves to intelligent students, should be attacked and carried out in the spirit of research, so that students may learn to ohserve, record and discover things themselves. In conclusion, { tender my sincere thanks to my colleague Mr Cousins, and also to Mr W. H. Hammond, Milton Chapel, Canterbury, and Dr A. B. Rendle, of the British Museum (Natural History Department), for valuable criticism and assist- ance in reading through the proofs. JOHN PERCIVAL. SouTH-EasTERN AGRICULTURAL COLLEGE, Wve, KENT. March, 1900. PREFACE TO THE SECOND EDITION THE very appreciative reception and rapid sale of the first edition have proved that a real want has been met by the book. The present edition has been emended and revised throughout in accordance with recent work and the criticisms of botanical friends. I shall be grateful for any further suggestions which may be deemed necessary to render the work more complete for educa- tional purposes or more useful to the student of this and allied branches of applied botany. JOHN PERCIVAL. Nov. 1901. PREFACE Vil PREFACE TO THE FOURTH EDITION To this edition a new chapter has been added and very consider- able additions made throughout the work, with a view of improving its usefulness and keeping the matter up to date. It is gratifying to find that the volume is highly appreciated by teachers and students in all countries wherever English is spoken. JOHN PERCIVAL. J IgIo. X CONTENTS PART II. INTERNAL MORPHOLOGY (ANATOMY). CHAPTER PAGE IX. THE PLANT CELL: CELL-DIVISION: TISSUES . » Io04 The cell, 105; Cell-division; Continuity of protoplasm, 110; Tissues, III. X. THE ANATOMY OF THE STEM, ROOT AND LEAF . #E3 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; The growing-points of stems and roots, 148. PART III. PHYSIOLOGY OF PLANTS. XI. THE CHEMICAL COMPOSITION OF PLANTS 2 ee 7 Carbohydrates, 155; Fats and fixed oils, 163; Volatile or essential oils, 164; Organic acids, 164; Proteins or Albuminoids, 165; Amides, 166; Alkaloids, 167. XII. THE COMPOSITION OF PLANTS (continued) . . 168 The elementary constituents of plants, 168; Water-culture, 169; Essential elementary constituents of plants, 171; Non-essential elementary constituents, 175. XIII. OSMOSIS ; ABSORPTION OF WATER i 177 Osmosis, 177; Absorption of water, 182; Exudation pressure; Root pressure ; ‘ bleeding’ of plants, 186. XIV. TRANSPIRATION: THE TRANSPIRATION-CURRENT . IQI Transpiration, 191; Transpiration-current, 198. XV. THE ABSORPTION OF FOOD-MATERIALS . . 201 Food and food-materials, 201; Food-materials and their ab- sorption, 202. XVI. ‘CARBON-FIXATION, ‘ASSIMILATION’ or ‘PHOTO- SYNTHESIS’ . . : ‘ ‘ - 208 ve CONTENTS CHAPTER XVII. FORMATION OF PROTEINS. TRANSLOCATION AND STORAGE OF FOODS : ‘ 7 Formation of proteins, 217; Utilisation, translocation and storage of plant-foods, 219; Nutrition of semi-parasites and semi-sapro- phytes, 225. XVIII. ENZYMES AND THE DIGESTION OF RESERVE- MATERIALS XIX. RESPIRATION . ? : 5 . : Ordinary respiration in the presence of free oxygen of the atmo- sphere: aerobic respiration, 233; Anaerobic or Intramolecular respiration, 238. XX. GROWTH ; : : Growth, 240; Conditions which influence growth, 243; spontane- ous movements of growth ; nutation and tissue-tension, 247 ; induced movements of growth, 250. XXI. REPRODUCTION ; : ‘ : Vegetative reproduction, 258; Cuttings, 259; Layers, 261; Budding and grafting, 262. XXII. REPRODUCTION (continued) Sexual reproduction, 269; Structure and germination of the pollen-grain, 269; The ovule and its structure, 271; Fertilisation and its effects, 273; Pollination; Self-fertilisation and Cross- fertilisation, 279; Transference of pollen, 281; Sexual affinity ; hybridisation and hybrids, 285; Mendelian laws of inheritance, 289 ; Artificial pollination ; methods of crossing plants, 299. . XXIII. CULTIVATED PLANTS AND THEIR ORIGIN; PLANT BREEDING . a yi . Bud-varieties or ‘ sports,’ 304; Variation among seedling plants, 305; Variations, how induced, 312; Correlated variability, 316; Reversion, ‘throwing back’ or atavism; Degeneration of varieties, 317. PART IV. CLASSIFICATION AND SPECIAL BOTANY OF FARM CROPS. XXIV. THE CLASSIFICATION OF PLANTS Individual and species; variety and race, 321; Genus; plant- names, 321 ; Divisions of the Vegetable Kingdom, 323. PAGE 217 227 233 240 258 303 320 X11 CONTENTS CHAPTER XXV. CANNABACEZ é . 5 . . The Japanese Hop, 332; The common Hop, 332; Hemp, 348. XXVI. CHENOPODIACEZ Sea Beet, 351; Common Beet, 351; Mangel Wourzel, $527 ee Beet, 36r. XXVII. CRUCIFERE . - : . Wild Cabbage, 366; Cultivated cabbage and its varieties, ee Turnip, 371; Swede, 376; Rape, cole or coleseed, 379; Black mustard, 381; White mustard, 383; Charlock, 385; Wild Radish, 386. XXVIII. LINACEA a . . . . General characters of the Order, 389; "Flax or Linseed, 389. XXIX. ROSACEZ Plums and Cherries, 397; Sloe, pales, Wild Sita and Apion, 399; Dwarf Cherry, Gean, Bird Cherry, Almond, Peach, 400; Strawberries, gor ; Raspberry and Blackberry, 403; Dog Rose, 404; Pear, 405; Apple, 406; Medlar, Whitethorn and Quince, 407; Lesser Burnet, 408. XXX. LEGUMINOS& é . . Peas, 412; Bean, 416; Vetch, 418; Vetchling, 420; Red Asie 421; Zig-zag clover, 424; Alsike, 425; White clover, 425; Crimson clover, 426; Yellow suckling, 428; Hop clover, 428; Black medick, 429; Lucerne, 429; Melilot, 432; Sainfoin, 432; Serradella, 434; Kidney Vetch, 434; Bird’s-foot trefoil, 435; Gorse, 436; Rest- Harrow, 437; Lupins, 437. XXXI. UMBELLIFERZ ‘ i, : Wild carrot, 444; Cultivated carrot, 444; Parsnip, 452; Hevioek, 454; Water Hemlock or Cowbane, 454; Water Dropwort, 455; Fool's Parsley, 455. XXXII. SOLANACEZ . , : Potato, 456; Bitter-Sweet, 468: Black nightshade, 468 ; Deadly nightshade, 468; Henbane, 469. XXXIII. COMPOSITA General characters of the Order, 470; Yarrow; Millefoil or Thousand-leaf, 473. XXXIV. GRAMINEZ. TRUE GRASSES i XXXV. GRAMINEE (continued). CEREALS . é PAGE 332 359 365 389 397 410 44t 456 470 475 483 CONTENTS Xill CHAPTER PAGE XXXVI. CULTIVATED AND WILD Oats (Genus Avena). 493 Wild Oat, 493; Bristle-pointed Oat, 494; Animated or Fly Oat, 494; Short Oat, 494; Common Cultivated Oats, 494. XXXVII. CULTIVATED BARLEYS (Genus Hordeum) - 500 Cultivated Barleys, 501; Distinguishing features of Barley-grains, 506; Characters of a good malting barley, 508. XXXVIII. CULTIVATED RYE (Genus Secale) . - 512 XXXIX. CULTIVATED WHEATS (Genus 77iticum) - 515 XL. COMMON GRASSES OF THE FARM : + 530 XLI. GRASSES AND CLOVERS FOR TEMPORARY AND PERMANENT PASTURES . : » 556 Grasses and clovers for leys of one, two or three years’ duration, 558; Grasses and clovers for temporary pastures lasting from three to six years; Grasses and clovers for permanent pasture, 561 ; Weight of seed to be used, 569. PART V. WEEDS OF THE FARM. XLII. WEEDS: GENERAL. 3 . . . 571 Their injurious effects, 571; Mistletoe, 575; Duration of weeds, 577; Habit of growth of weeds, 579; How weeds are spread, 580; Extermination of weeds, 582. XLII]. WEEDS: SPECIAL . 7 ‘ ‘ .. 589 Weeds of arable ground, 589 ; Weeds of pastures, 604. PART VI. FARM SEEDS. XLIV. FARM SEEDS: GENERAL . . . - 614 Purity, 616; Germination Capacity, 620; Speed of germination or germination energy, 626; Weight, 629; Form, colour, bright- ness and smell, 635. XLV. FARM SEEDS: SPECIAL . . . + 639 XIV CONTENTS PART VII. FUNGI, CONSIDERED CHIEFLY IN RELATION TO SOME COMMON DISEASES OF PLANTS. CHAPTER PAGE XLVI. FuNGI: GENERAL. ; : - 677 Hypha and mycelium, 677; Reproduction, 679; Germination of spores, 682; Mode of Life; saprophytesand parasites, 683 ; General advice to be followed when dealing with plant diseases, 686. XLVII. FuNGI (continued) PHYCOMYCETES .« ‘ - 688 Eumycetes, 688 ; Phycomycetes (sub-class i. Zygomycetes), 689. XLVIII. FUNGI (continued) PHYCOMYCETES . é . 692 Phycomycetes (sub-class ii. Oomycetes), 692; Damping-off, 693 ; Potato diseases, 698. XLIX. FUNGI (continued) BASIDIOMYCETES 5 ¢ 715 ‘Smut’ of Oats, 716; ‘Smuts’ of wheat, barley and rye, 718; Bunt of wheat, 723; Rust and mildew of wheat, 726; Other species of Rusts, 735; The common mushroom, 740. L. FUNGI (continued) ASCOMYCETES ‘ - 745 Yeasts, 746; Mildews, 748; Ergot, 758. LI. ‘CLuUB-ROOT’ DISEASE ‘ ‘ : - 763 PART VIIL. BACTERIA. LII. BACTERIA: THEIR MORPHOLOGY AND REPRODUC- TION : ‘ ‘ s - 769 Forms of Bacteria, 769 ; Vegetative reproduction, 770; Reproduc- tion by means of spores, 771; Conditions affecting development, 774; Sterilisation and pasteurisation, 776. LIII. BACTERIA: THEIR WORK : . 779 Lactic fermentations, 780; Butyric fermentations, 782; Acetic fermentations, 784; Fermentation of cellulose, 785; Fermentation of urea, 786; Putrefaction, 787; Nitrification, 789; Denitrification, 792; Fixation of free nitrogen, 793; Bacteria and diseases of animals, 803; Diseases of plants caused by bacteria, 805; Black rot of cabbages, 806. PART I. GENERAL EXTERNAL MORPHOLOGY. CHAPTER I. INTRODUCTORY. 1. THE things met with every day can be separated into two dis- tinct 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 plants. The term Biology in its widest 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 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, A z 2 INTRODUCTORY 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 sub- stances as food-materials resemble plants, but which are never- theless 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 pro- duce 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 sub- stance 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 INTRODUCTORY 3 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 norphology 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 con- venience 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 differ- ent 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 Sperma- phytes 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, 4 INTRODUCTORY 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 peren- nials. 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 pro- duce 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, (1) 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 INTRODUCTORY 5 end of the growing season, the parts of the plant which still remain to carry on growth in subsequent years being under- ground: the stinging nettle, hop, and potato are representa- tives of this class. In woody perennials, of which all trees and shrubs are exampies, 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 branch- ing. 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 ot the cereals and ‘roots’—mangels, turnips, swedes and carrots—on the first day of each month during a whole year, and make careful 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 peren- nials, consequéntly somewhat arbitrary, they are sometimes placed in groups according to the number of times they are able to produce seeds. Those which yield only one crop and then die are termed 6 INTRODUCTORY 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 flowers and seeds during an indefinite number of seasons are described as polycarpic CHAPTER II. SEEDS: THEIR STRUCTURE AND GERMINATION. 1. Iv is well known that one of the most ordinary methods of raising plants is to sow what are called seeds, yet how few there are among the many who use them who fully appreciate their real 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 inanagement 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 neces- sary 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 Fic. 1.—Piece of bean pod showing the funicle (/) a short stalk or funicle and its attached seed. (Fig. 1), and it is through this stalk that all the nourishment 7 8 SEEDS: STRUCTURE AND GERMINATION 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; 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 de- tached 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 A7/um 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 micropy/e, easily seen with a lens, and through which water oozes out usually accompanied by bubbles of air when soaked beans are squeezed be- ¢ tween the finger and thumb. This open- % ing communicates 7 with the interior of the seed, and is the only one it possesses. Fic. 2.—Bean embryo, show- Fic. 3.—The same as Fig. 2 itti ing (~) radicle and (c) after removal of one coty- On slitting round cotyledon. ledon; 7 radicle; 6 the 1 i plumule; ¢ cotyledon of the edge with a knife, embryo. the outer part of the bean can be stripped off as a pale, semi-transparent, leathery membrane ; this is known as the /esfa or seed-coat, and is thickest THE COMMON BEAN 9 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 coty/edons (Fig. 3, ¢), which, however, are not completely separate from each other, but connected at the side with a conical projecting body (Fig. 3, ~), 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, ~) elongates and breaks its way through the 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. This plantlet is called an embryo, and the portion of it which 10 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 vadicle, and consists of a very small piece of stem, the Aypocoty/, at the end of which is a voot. 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 cotyle- dons is the plumule of the embryo, and consists of a very short piece of stem, the epzcoty/, 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 littl Fic. 4.—Bean embryo after four days' growth. of a >. the part of the One cotyledon has been removed. ¢ Coty- stem which grows most being ledon; 7 primary root; & epicotyl with = i contd atts tp. the epicotyl. It is on account er re of the elongation of this portion of the plantlet that the plumule with its young leaves are driven above ground, the cotyledons remaining below en- closed 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 II 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 a 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 come 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 embryo in the seed is being fed by the parent and visibly grows until ripeness is attained. The young plant then assumes a dor- mant or resting state within the seed without showing any signs of life. Under certain conditions, however, the plantlet begins to wake up, and soon escapes from its protective coat to lead a 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 (1) water, (2) heat, and (3) air or oxygen. It is also essential, of course, that the plantlet in the seed must be alive. The exact nature of the dormant state of seeds is not 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 germina- tion 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 on this point more will be said in a later chapter. For present purposes it will suffice merely to mention that age is a deter- 12 SEEDS: STRUCTURE AND GERMINATION mining 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. When 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 hilum. 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 absorp- tion 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 sddes of the seeds, leaving the micropyle and hilum untouched. Weigh both lots 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 again, 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 con- dition, 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 13 their radicles and push their way through the seed-coat even if just kept above freezing point; others requiré a temperature of 9° or 10° C. tostart growth. If attempts are made to grow beans at 45° C. it will be found to be too hot, and they make little or no progress. Between this high temperature at which growth appears impossible, and the freezing point where the develop- ment of the embryo of the bean is also suspended, there is a temperature at which the embryo makes the most rapid progress, and 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. Ex. 5.—Arrange two separate lots of similar-sized beans soaked for the same length of time in damp flannel as described in Ex. 3, and place one in a warm kitchen and the other in a cold cellar. Observe which show their radicles first. 5. The supply of fresh air is also an essential condition for growth of the young plant from the bean seed, but the evidence for its need is not so manifest or so generally recognised as the necessity for moisture and warmth. It will be found, however, when beans are placed in a flask or bottle containing carbon dioxide or hydrogen gas they refuse to germinate, even when they are sup- plied with a proper amount of water, and kept at summer heat. Ex. 6.—Place ten soaked beans in a wide-necked bottle. Fill the bottle with carbon dioxide gas or coal gas, and cork it up with a tightly-fitting indiarubber stopper. Arrange another bottle in the same way, but with ordinary air in it instead, Take out the stopper of this one twice daily and blow in fresh air, so as to ensure a good supply to the seeds. Place both in a warm situation and observe which germinate best. 6. The peculiar extension or growth of the parts of the interior of the bean seed, and the fact that a suitable supply of water, air and heat is necessary for the manifestation of these changes, suggests to us that we are dealing with a living structure. This becomes all the more apparent when we observe that the oxygen 14 SEEDS: STRUCTURE AND GERMINATION of the air is absorbed, and in its place carbon dioxide is given off into the surrounding air, for this is what happens in the breathing of a iiving animal. Ex. 7.—Carbon dioxide is produced when beans germinate. Place twenty soaked beans in a wide-mouthed bottle, and cork them up after showing that a match burns freely in the bottle. Leave them in a warm place for twenty- four hours, and try if a match will now burn in the bottle. The carbon dioxide gas can be poured out into a beaker containing lime water; on shaking, its presence is proved by the lime water becoming ‘milky ’ owing to the precipitation of carbonate of lime. The particular use of the water, heat and air to the plant we cannot at present discuss. It may, however, be mentioned that without water the embryo would have little chance of becoming free from the tough and hard seed-coat surrounding it; water softens the latter, and makes it more easily torn by the extending radicle and plumule. In the early stages of the life of the bean plant, from the com- mencement of germination up to the time when the first green leaves are unfolded, the development and building up of the elongating rootlet and shoot depend upon the thick cotyledons. At first the latter are thick and fleshy, but as the radicle and plumule grow the cotyledons become softer and thinner, ulti- mately shrivelling considerably. The cotyledons are leaves, the interior of which is packed with food for the rest of the growing embryo, and a large amount of the water absorbed by the séed is used for the purpose of dissolving the nutrient material in them, and carrying it from them to the various parts of the root and shoot of the young plant where growth is going on. Ex, 8.—Germinate beans in damp flannel as in Ex. 3, and show that the cotyledons are essential to the development of the root and shoot of the em- bryo by cutting them off as soon as the two latter parts have emerged from the seed-coat. Try separating one cotyledon and then two at various stages of development, and see if the axis (root and shoot) can be made to develop without them. The growth should be allowed to continue some time in order to obtain well-marked effects. 7. Not only do the changes observed in the embryo of a ger- THE COMMON BEAN 15 minating bean point to the conclusion that it is a living structure and like an animal dependent on a proper supply of water, heat and air for the manifestation of its life, but the parts of a young bean plant after emerging from the seed soon give evidence of the possession of peculiarities which are associated with life. When put in the ground, the radicle, in coming out of the seed, turns straight downwards and continues to grow in this direction. This is the case no matter in what position the seed is placed. If, after germination has commenced, it is taken and replanted with the primary root pointing to the surface of the soil, the tip of the root soon begins to curve downwards again, and will maintain this course until again disturbed. The plumule behaves in exactly the opposite manner ; after emerging from the seed-coat its bent tip grows upwards and away from the root; if the seed is reversed and replanted the plumule begins to curve in such a manner that its tip is driven upwards towards the surface of the ground. That these peculi- arities are somehow connected with life is clear, as dead embryos show no such behaviour. Ex. 9.—Sow soaked beans in a flower pot or box filled with ordinary garden soil placing them in various positions in it, some laid on the flat side, some with the hilum directed upwards, and others with the hilum downwards, Allow them to grow in a warm place : take them up as soon as signs of germin- ation are noticed, and observe the direction the root and shoot have taken. The peculiar tendency for the root always to go downwards and stem upwards can be investigated by sowing beans in ordinary garden soil and afterwards reversing them. To avoid error all should be taken up, and then placed again in the soil-in various positions—some as they were, a few with their roots and stems reversed, and others laid in a horizontal position. They may be re-examined at the end of a week. Another method of showing the same peculiarity may be carried out thus :—Germinate soaked beans in damp flannel as in Ex. 3. When the roots have extended about half an inch take two seeds and suspend them by means of thread side by side in a bottle with their roots downwards and stem upwards. The bottle should contain a little water to keep the air damp. When the roots have grown about two inches reverse one of the seeds so that its root points upwards and stem downwards. Notice that the tip of the 16 SEEDS: STRUCTURE AND GERMINATION root of the reversed seed in about twelve hours begins to turn downwards, while the plumule more slowly bends in such a way as to assume the position it had before it was reversed. The bottle should be placed in a dark box o1 cupboard to avoid the influence of light on the plant, and fresh air should be blown into the bottle twice a day. 8. Although seeds vary almost indefinitely in regard to size and shape they are similar to the bean in so far as they all contain a young plant packed away within the seed-coats. In this essential feature all seeds agree with few exceptions, and it is on account of the existence of a young plant within them that they are of use in the raising of crops or plants. The manner, however, in which the embryo is arranged, and the relative size and appearance of its various parts, differ con- siderably in seeds; moreover, the growth during and after germination is not the same in all cases. A few of the more important and common variations in these respects must be noticed. White Mustard.—The seed of white mustard (S:zafis alba L.) contains an embryo which like that of the bean consists of a radicle, plumule and two cotyledons; the latter, which are folded together, are relatively thinner than those of the bean and deeply notched as in Fig. 5. The radicle is bent round and lies in the fold of the cotyledons, between which is the very small, almost invisible plumule. On germination the cotyledons, instead of remaining within the seed-coat and below the ground as in the case of the broad bean, escape from the enclosing coats altogether and grow up out of the ground, enlarging at the same time, and becoming green like ordinary leaves. They are the first ‘smooth’ leaves of the seedling mustard plant. After a short time the plumule grows up from between the cotyledons and forms a stem upon which are gradually unfolded the ordinary divided ‘ rough’ leaves. Ex. 10.—Soak white mustard seeds, and examine their structure, noting especially the way in which the embryos are packed in them. Allow some to WHITE MUSTARD 17 germinate and grow for a week or more on damp flannel, and examine them in various stages of development, noting the notched cotyledons with small Fic. 5 —1. Seed of White Mustard. 2. Folded embryo as seen after removal of seed-coat. 3. The same unfolded. 4. Seed ger- minating. 5. Young seediing. 6. Same as 5, but a week older. ¢ Cotyledons or ‘smooth leaves’; % hypocotyl ; ry radicle and primary root; /first foliage leaf (‘rough leaf’); 4 petiole of another leaf similar to 7 with blade removed ; 4 terminal bud; x surface of the soil. plumule, well-marked hypocotyl, and distinct separation between the latter and the root. B 18 SEEDS: STRUCTURE AND GERMINATION g. The term Aygogean is applied to cotyledons which remain below ground, those coming above being efigean, the relative amount of growth in the hypocotyl and epicotyl determining their position. If the hypocotyl grows vigorously during or after germination the cotyledons are forced above ground ; when only the epicotyl grows the plumule is lifted up above the soil, but the cotyledons remain below where the seed is placed. In the broad bean the hypocotyl is very short, and the point where it ends and the root begins is not clearly defined. In a mustard seedling, however, the point of separation between the root and stem is somewhat swollen and readily distinguished (Fig. 5). 10. All plants whose embryos, like those of the bean and mustard, possess two cotyledons, are known as Dicotyledons ; they form a very large, well-marked class of the flowering or seed-bearing plants. 11. The seeds hitherto mentioned contain within their coats nothing but an embryo plant, which depends for the develop- ment of its root and shoot upon the substances stored up in some part of its body, its cotyledons chiefly. This is true even in the case of seeds like those of white mustard, in which the cotyledons of the embryo are comparatively thin. There are, however, a number of plants, such as the ash, mangel and potato, which, although belonging to the Dicotyledons, have seeds in which there are stores of food inside the seed-coat, but free from the embryo and its cotyledons (Fig. 109). Such separate reserve-food, whatever its chemical composition may be, is known as endosperm or ‘albumen,’ and seeds in which it is present are called enxdospermous or albuminows seeds. Those like the bean, pea, and vetch, mustard, and turnip, which have no separate reserve-food, are known as exendospermous or exalbuminous seeds. Ex. 11,—Take out a seed from the fruit of the ash tree in autumn ; carefully cut thin shavings from the flat side of the seed, starting about the middle of ONION 19 the seed and cutting towards the narrow end. Note the white embryo with its well-marked radicle, hypocotyl and two flat cotyledons lying within the semi-transparent endosperm, 12. Some of the most commonly occurring endospermous seeds will be found to have embryos within them which are not dicotyledonous, and whose structure is in many respects very different from those we have hitherto mentioned.