faba Nc 2 Cornell Muiversity Library BOUGHT WITH THE INCOME FROM THE ad SAGE ENDOWMENT FUND THE GIFT OF Henry W. Sage 1891 MOY 2 se crs Yh, Uy fli 2... , 4 Ainge ELEMENTARY BOTANY GEORGE BELL & SONS LONDON : YORK STREET, COVENT GARDEN NEW YORK: 66 FIFTH AVENUE, AND BOMBAY : 53 ESPLANADE ROAD CAMBRIDGE: DEIGHTON BELL AND CO. ELEMENTARY BOTANY BY PERCY GROOM, M.A.(Cantab. et Oxon.), F.L.S. Examiner in Botany to the University of Oxford, and sometime Professor of Botany at Whampoa (China) WITH 275 ILLUSTRATIONS LONDON GEORGE BELL & SONS 1898 QD PREFACE In writing the present volume, I have endeavoured to place the subject before elementary students in such a way as to exercise to the full their powers of observation, and to enable them to make accurate deductions for themselves from the facts which they observe. To attempt. the study of Botany without the practical examination of plants is futile. Students of plant-life must look at plants, and this book is specially designed for use during the process. Considerable experience as examiner in Botany as taught in schools has convinced me that comparatively few learners have the advantage of seeing specimens with the aid of a compound microscope, although the treatises usually employed should involve the frequent use of such an instrument. Under these circumstances, I have in the following pages assumed that a compound microscope is not employed, and for their proper understanding such an instrument is quite unnecessary. An ordinary inexpensive lens should be used to aid the naked eye; but, on the other hand, in commencing the study of Botany a compound microscope is absolutely needless, and, in the case of young beginners, does more harm than good. The section on Physiology has been so written that no knowledge of the histology of plants is assumed—a feature which is, I believe, here introduced for the first time. Though by no means a “cram-book” for elementary examinations, a thorough know- ledge of the contents of this book will enable a candidate to pass with distinction. In order to lay more emphasis on the observation of facts, and with a view to simplify the whole matter, I have inserted no unnecessary technical terms, but, for the convenience of students who afterward use ‘‘Floras,” I have added an appendix for use as a dictionary, but not for the purpose of elementary study. vi PREF ACE Some words of explanation may be required in reference to the definitions of flowers and fruits. In more advanced works we are told that a flower is a collection of sporophylls inserted on a simple axis. This definition seems to me im- * perfect. That the young carpels and stamens are homologous with leaves, and particularly with sporophylls, is proved -beyond a doubt. But the mature carpel with the ripe ovules is no longer homologous with a sporophyll ; it is a sporophyll containing parasitic and symbiotic gametophytes. The sym- biosis of the gametophytes and the sporophylls before, during, and subsequent to fertilisation constitutes a phenomenon which is unique in the vegetable kingdom. Consequently, it appears that, when judged by the facts of the case and on historical grounds, it is at least incomplete and inexpedient to employ to the cone of Egudsetum the same term as to the flower of a Buttercup. A single flower of a Buttercup is no more a mere collection of sporophylls than a frog is a fish because it passes through the tadpole stage. In reference to the definition of a fruit, I have followed that given in the “Lehrbuch der Botariik” written by Professors Strasburger, Noll, Schenck, and Schimper. The definition of a fruit is thus brought closer to the popular usage of the term, while we are extricated from any dilemma in reference to distinguishing between an inferior and a false fruit. . In conclusion, it should be stated that for the most part the illustrations have, after careful consideration, been specially executed by my friend Mr A. H. Church of Jesus College, Oxford, to whose skill and care I am much indebted. To him, also, I owe a careful revision of the proofs of this book. Further assistance in the matter of illustrations has been rendered by Mr A. Robinson of the University Museum, Oxford. Students who desire a simple introduction to the study of Microscopical Botany are recommended to procure Dr D. H. Scott’s “Structural Botany”; while those who wish for a comprehensive work, dealing with the science as a whole, will find all they require in “The Student’s Text-book of Botany,” by Professor S. H. Vines. Finally, such students as desire to identify wild British plants,and to do field-work, will find Hayward’s “ Botanist’s Pocket Book” an excellent little work which contains all the necessary information. CONTENTS ParRT I.—GENERAL MORPHOLOGY CHAPTER I. IL. Ill. Iv. INTRODUCTION ROOT AND SHOOT ROOT" Adventitious Roses, 6 Shapes of, Roots, éWedat Roots, 8. VEGETATIVE SHOOT Adventitious Shoots, 11. ARRANGEMENT OF LEAVES Z Whorled Leaves, 11—Alternate Leaves, Bepeenie: 13. FOLIAGE-LEAVES Sheath, 1 5—Stalk, I eBiade: 16 pa of Blade, 6 —Venation of Blade, 16—Division of Blade, 17. SIMPLIFIED LEAVES 3 ‘ Scales, 18—Cotyledons, 19 —Bropivilsy 21—Bracts, 21. BUDS . Zstivation, 5a Newation, 23. STEM Definite and Indefinite Gromit hic chives of different Orders, 24—Sympodia, 2 5—Arrangement of Branches, 26—Herbaceous and Woody Stems, 27—Increase in Thickness, 27. SUBTERRANEAN SHOOTS . A . e Rhizome, 29—Tuber, 30—Corm, Life-history of Crocus, 30—Bulb, 32. SUB-ERIAL STEMS. . Direction of Growth, 33—Climbing Bidats, es Climbers, 34—T wining Plants, 34—Tendril-Climbers, 35, Scramblers, 36. PAGE II 14 18 22 24 28 33 vill CONTENTS CHAPTER VI. VIL. Vill. IX, XI. SUBSIDIARY OUTGROWTHS (HAIRS, ETC.) . METAMORPHOSED SHOOTS . : ‘a : Spines, Thorns, and Prickles, 37—Tendrils, 38— Cladodes, 38. LIFE-HISTORY OF FLOWERING PLANTS a < Frequency of Flowering and Duration of Life, 39— Methods of Resting, 4o— Methods of Vegetative Multiplication, 41—Order of Succession of Events, 42. FLOWER . “ ‘ o 3 Flower of Buttercup, 43—Flowers of Scotch Pine, 44— Definition of a Flower, 45. GYMNOSPERM£# :—-SCOTCH PINE INFLORESCENCE y r FS = . Racemose Inflorescences, 51—Cymose Inflorescences, 54—Bracts, 55. FLORAL LEAVES PERIANTH. . a é Calyx, 57—Corolla, 58—Perianth, 60. ANDRECIUM 7 i GYNACIUM . . $ 5 . Apocarpous Gynzcium, 63—Syncarpous Gynzcium, 64 —Placentation, 64—Absence of Stamens or Carpels, “66. . ARRANGEMENT OF THE FLORAL LEAVES . CYCLIC FLOWERS . . ‘ . p Obdiplostemony, 67—Unequal Growth, 68—Atrophy and Suppression, 69—Fusion or Cohesion, 69— Branching or Doubling, 69—Symmetry, 70. ACYCLIC AND HEMICYCLIC FLOWERS FLORAL DIAGRAMS : . fEstivation, 73—Floral Formule and Symbols, 74. SHAPE OF THE RECEPTACLE * . 6 Hypogynous Flowers, 74—Perigyrious Flowers, 75— Epigynous Flowers, 75—Other Modes of Insertion, (75—Disk, 76. NECTARIES POLLINATION . F > : Cross-pollination, 78— Arrangements for hindering Self-pollination, 78—Wind-pollinated Flowers, 79— Insect-pollinated Flowers, 80.—Self-pollination, 82. PAGE 36 39° 43 47 51 57 57 60 63 67 72 72 74 77 77 CONTENTS 1x CHAP. PAGE XH. OVULE . ‘ : : ‘ . 84 FERTILISATION AND CHANGES IN THE OVULE . 85 FRUIT ; 87 Classification of Simple Fruits, do: Compound Fruits, 94—Complete Fruits, 94. XIII. DISPERSAL OF SEEDS . F 95 Explosive Fruits, 95—Dispersal a the Wind, 95— Dispersal by Clinging to Animals, 96— Dispersal inside Animals, 96—Protection of the Embryo in the Seed, 97. FUNCTIONS OF THE PARTS OF FLOWERS, FRUITS, AND SEEDS : ; : , - 98 ParT I[I.—CLASSIFICATION OF ANGIOSPERMS XIV. CHIER CHARACTERS OF THE FAMILIES CONSIDERED 103 DICOTYLEDONS . » LOZ APETALZ, 107 — Capi 107— Siete 114— Euphorbiacez, 116. POLYPETAL#, 118—Ranunculacee, 118—Papaveracez, 123—Cruciferse, 124—Violacez, 127—-Caryophyllacez, 130—Malvacezx, 132—Geraniaceze, 135—Oxalidaceze, 137—Papilionacevze, 137—Rosaceze, 139 —Umbelliferze, 146. GAMOPETAL&, 148—Primulacez, 148—Convolvulacez, 151—Solanacee, 151—Boraginacer, 153—Labiate, 153 — Scrophulariacee, 156— Caprifoliacex, 159— Composite, 161. MONOCOTYLEDONS. : . 169 Liliacezee, 169—Amaryllidacez, 1 ie: aS dlabere: 17I— Orchidaceze » 175—Araceze, 178—Graminacee, 181. ParT III.—PHYSIOLOGY XV. NUTRITION OF THE PLANT : 189 Chemical Composition of a Plant, Bo Corpontion i the Air and Soil, 190—Artificial Culture-solutions, 191—Manufacture of Organic Compounds, 192. } x CONTENTS CHAP. XVI. ABSORPTION OF CARBONIC ACID . : Influence of Temperature, 194—Influence of Lighé, 194 —Chlorophyll, 194. XVII. ASSIMILATION OF CARBON . . Proteids, 196—Carbohydrates, 197—Fats, top Feria. tion of Starch, 198—Entrance of Carbonic Acid, 199 —Green Parts not producing Starch, 200—Why Light is Essential, 20o—Transport of Carbohydrates, 200—Starch, Sugar, Fats, as Food-substances, 201— Nutrition of Plants devoid of Chlorophyll, 202. XVIII. ABSORPTION OF WATER AND INORGANIC SALTS . Absorbing Functions of Roots, 203—Influence of Exter- nal Conditions, 204—Essential Chemical Elements and their Absorption, 205. ASCENT OF WATER AND SALTS ‘ . XIX. TRANSPIRATION Measurement of Pana sieatie, co as Tran- spiring Organs, 210—Conditions influencing Tran- spiration, 210—Function of Transpiration, 211. EXCRETION OF LIQUID WATER . ROOT-PRESSURE . CAUSE OF ASCENT OF WATER XX. RESPIRATION . . Oxygen essential to Flowering Plants, Fp oondtiens affecting Respiration, 217—Liberation of Heat during Respiration, 218. XXI. GROWTH . . ei . é Essential Conditions, see ciara in Length, 220— Rate of Growth in Length, 220—Influence of Tem- perature, 220—Influence of Water-supply, 220— Influence of Light, 221—Nutation, 221—Direction of Growth in Length, 221-—Heliotropism, 221— Geotropism, 222—Hydrotropism, 222. XXII. IRRITABILITY AND MOVEMENTS OF LIVING PARTS. Periodic Movements, 224— Irritability of Moving Organs, 226. APPENDIX . . . . fi é INDEX . . . . . é , PAGE 193 196 203 206 209 212 213 214 215 219 224 229 239 PART I GENERAL MORPHOLOGY ELEMENTARY BOTANY CHAPTER I INTRODUCTION Puants, like animals, are living beings, and may be regarded from two standpoints. In the first place, a plant may be con- sidered as a living machine designed to execute certain work and consisting of definite parts or o7gans, to each of which there is allotted a particular office or function. After this definition we naturally inquire how a plant lives, feeds, grows, and multiplies. We then ask precisely what work is performed by the various organs, such as the leaves, stems, and roots. This aspect of botany is termed Physiology. Again, we may look at a plant simply as a machine consisting of various parts or members, which are arranged in a particular order and have certain shapes. In fact, we learn the exact form of the plant without taking notice of the work it does. This department of botany is termed Morphology. Studied from this point of view, we find that plants exhibit resemblances to, and differences from, one another. For instance, a Fern seems very unlike a Mushroom, and yet both are alike in so far as neither of them possesses flowers. On the other hand, a tuft of Grass and a Buttercup are widely different in appearance, but at the same time they resemble each other insomuch as they both produce true seeds from flowers. These points of likeness and unlikeness among plants lead us to arrange the latter into groups. This grouping is described as Classification, and constitutes Systematic Botany. For our present purpose, let us be content to divide plants into two great classes— namely, Mowering Plants and Non-Flowering Plants. In the first group are included all plants which bear seed-producing flowers, whether they have showy blossoms such as those of the Buttercup, Wallflower, and Dandelion, or blossoms which we hardly notice, such as those of Grasses, Oaks, and Hazels. Non-Flowering Plants bear no seed-producing flowers: amongst A 2 INTRODUCTION them are the Ferns, Mosses, Seaweeds, and Fungi. In this book we treat only of flowering plants, so far as they can be studied with the naked eye aided by a simple lens. Method of using this book.—This book is divided into three Parts:—Part I. relating to General Morphology (and ‘ including a special chapter on the Scotch Pine); Part II. referring to the Classification of Angiosperms; and Part III. relating to the Physiology of plants. Beginners should first read chapters il. to v. in Part I, and should practically examine the roots, stems, and leaves described. They may then pass on to the study of Physi- ology contained in Part III. (chapters xv. to xxii.); or they may read the remaining chapters of Part I. (omitting that which relates to the Scotch Pine), at the same time studying the families specially marked at the commence- ment of Part II. (chapter xiv.). In this book the char- acters of each family are denoted by a description of one or more representatives which are “yes. of that family. While a student is reading the description of one of these types, he must have before him a specimen of the plant described, so that he can constantly examine and refer to it. Should any point in the description be beyond the compre- hension of the learner, reference should be made to the teacher or, by means of the index, to the explanations given in Part I. The families should not be studied in the exact order in which they are placed in the book: the season of the year and other considerations will determine the order in which the types are to be examined. As examples of flowers appropriate for beginners we may mention the Buttercup, Poppy, Wallflower, Pea, Rose, Primrose, Dead Nettle, Hyacinth, and Daffodil. In beginning the study of the types for the first time, students should entirely ignore, and omit to read, the characters given at the commencement of the description of each family. If the beginner has studied the systematic portion of the book. thus outlined before working at the Physiology, he should then pass on to Part ITI. Finally, when the student has acted as previously advised, the whole of Part I. should be read over again: and the remaining types and families in Part II. might also be dealt with. : CHAPTER II THE DISTINCTION OF A FLOWERING PLANT INTO ROOT AND SHOOT EVERYONE is familiar with the fact that ordinary flowering plants possess roots, stems, leaves, and flowers. The roots cf a plant constitute its root-system, and are usually concealed in the soil; whereas the stems, leaves, and: flowers of the plant together compose the shoot-system, and are generally visible and above ground. But stems and leaves are occasion- ally embedded in the soil; whilst roots may be found raised above the ground on sub-aerial parts of the plant. Hence we cannot define a root as being the subterranean part of the plant, nor the shoot as being the sub-aerial portion. It will, therefore, be well to consider first what we mean by the terms “root” and “shoot.” For this purpose the seedling of a bean may be examined. The seedling consists of a main axis, which bears certain structures—the lateral members— on its sides. The ascending portion of this axis is the stem, which possesses the flattened leaves as its lateral members. At the tip of the stem the leaves are crowded together to form a bud. The main stem may also produce lateral stems—the branches—which are like itself. The descending part of the main, axis of the seedling is the main root, which has no leaves, and therefore. does not terminate ina bud.* The root does, however, bear branches similar to itself which are called the lateral roots. } Even inside the seed of the Bean, the young plant, or embryo, displays this distinction into root and shoot. The bean-seed (fig. 1) is externally clothed by a shell-like seed-coat termed the testa (ts). The testa has a minute pore (wm) at one end of the scar (Az) on its side. The whole of the space enclosed within * The tip of the root is covered by a little cap termed the voot-cap, which can only be properly seen by the aid of a compound microscope. 3 4 ROOT AND SHOOT the testa is occupied by the embryo. The embryo (fig. 2) has a small rod-like main axis, which is composed of the primary or main root, the vadicle (7); the primary or main stem (f/); and a part of the axis, the Aypocoty/ (hp), which connects the root and stem. The tip of the young root lies close within the pore of the testa. No lateral roots occur on the radicle at this stage. The main body of the embryo is constituted of the two large fleshy leaves—the cotyledons (cot), which are attached to that rN syn m Fig. 1.—Seed of Bean. Fig. 2.—Embryo of Bean, with Cotyledons separated. portion of the axis which is termed the hypocotyl. Lying hidden between the two cotyledons is the minute main stem, which terminates in a small bud. Thus, beginning at the root, the axis has no lateral members on its root-portion: above succeeds the hypocotyl* with two lateral cotyledons: still higher the axis represents the young main stem, and bears a few lateral commencements of leaves. When the seed germinates, the various parts of the embryo emerge. The radicle elongates and becomes the primary root: it grows -downwards and produces lateral roots which may branch in their turn. The little stem grows upwards and sends out from its sides, leaves, branches, and flowers ; its branches may in turn bear, not only leaves, but also branches of their own. We thus see that the development of this flowering plant from its emktryo consists in the elongation of its primary axis, and the production of lateral members on that axis. The parts possessed by a mature flowering plant, whether it be a large tree or a small herb, are all to be traced back to the primary axis. * It is impossible to define exactly the limits of the hypocotyl unless the compound microscope be employed. ROOT 5 We can now define a root anda shoot. A stem ts an axis which bears lateral members—the leaves—adissimilar to itself. A stem together with its leaves constitutes a shoot. A shoot terminates in a bud, and is usually the ascending portion of the plant: at least, parts of it are generally green. Lastly, the shoot bears the flowers. A voot ts an axts which cannot produce leaves as lateral members of itself: consequently it does not terminate in a bud.* A root can only produce as lateral members branches like itself: as a rule it is a descending axis, and has no green colouring-matter. THE ROOT. If we fix a germinating bean (or pea) in a bottle contain- ing air which is saturated with moisture, in the manner shown in fig. 3, when once the root has commenced to grow straight, we can follow the method of growth. To accomplish this, we make a number of transverse marks in Indian ink at equal and short distances along the root. After twenty-four hours’ growth it will be found that the distance be- tween the consecutive marks remains. the same, excepting near the tip of the root, where the marks have become separated by longer intervals. This shows that the root increases in length by elongation which only takes place in the region of its apex: conse- quently, the youngest part of a root is that which is nearest its apex, whereas the oldest is that nearest its base. A short distance behind its apex (fig. 4 7x) the root has a broad encircling band of fine silky hairs—root-hairs (72). As the root grows at its apex new root-hairs form constantly behind the tip, which, of course, has been carried forward, so that the youngest root-hairs are those nearest the tip. These hairs live for a short time only, for they soon shrivel and peel off, and therefore they are found solely on the young and more terminal portions of a root. A root may bear branches structurally similar to itself. These arise on the main root ‘at points nearer to the root-. * It has a root-cap, which is not possessed by a stem. 6 . ROOT apex than the last-formed lateral roots; so that the youngest ' and smallest of them are seen to be nearest to the tip of the main root (fig. 4). Zhe Jateral roots are therefore said’ to arise in acropetal succession. They do not appear at indifferent points; on the contrary, they emerge only on certain determined sides of the main root, so as to form regular ranks or rows along the length of the latter. For 2 = ale hi ceeceseer en Ob To) S @ i( WW. she l ® Ue Vz G wy re AA] TMD A 3 Oe etl Ly 2 ; Th Pee 7 | a . k Fig. 4.—Development of a typical Dicotyledon. example, the branches of a Wallflower-root form two rows, while those of the Creeping Buttercup-root are ranged in four rows.* Adventitious Roots.—Lateral roots frequently arise on stems —for instance, on the creeping stems of the Strawberry (fig. 54), Creeping Buttercup, and Grasses; or on the under- ground parts of the stem of the Primrose or on “Cuttings.” Inasmuch as these roots do not arise in the normal method— * One important character concerning the origin of lateral roots is that they arise as internal growths, which push their way through the rind of the mother-root, and eventually reach the soil. They are said to be endogenous (arising within) in origin. : ROOT 4 that is, as acropetal branches of another root — they are said to be adventitious. The difference between adventi- tious and normal lateral roots is well illustrated by considering the root-system of Diécotyledons and Monocotyledons. One of the general characteristics of a Dicotyledon is that its embryo in the seed has two cotyledons (¢.g. Bean, Hazel, Oak). Frequently the root-system of Dicotyledons is formed after the manner described as occurring in the Bean, and well illustrated by fig. 4. The embryo of a Monocotyledon, on Fig. 5.—Development of a typical Monocotyledon. the other hand, possesses only one cotyledon (¢.g. Grasses, Lilies). Nearly always the root-system of a Monocoty- ledon develops in a manner entirely different from that pursued by the Bean. The young primary root (R) of the embryo grows for a short time only and produces at the most few lateral roots, eventually shrivelling up; but, sooner or later, lateral roots arise successively higher up the stem, first on the hypocotyl (a), then on the stem (2)—as is denoted in fig. 5. Consequently, in full-grown Monocotyledons practically the whole root-system is adventitious, and there is no main-root with branches. [In fig. 5 the roots have pulled the base of the shoot down into the soil.] 8 ROOT Shapes of Roots.—The roots may be thin and fibrous, or they may present various forms between this and a swollen or tuberous condition. The main root of the Carrot and Turnip, thickens and forms the swollen part which we eat. The Dahlia-plant produces a number of adventitious tuberous roots, which grow out from the base of the stem. As will be shown later on, these thick fleshy roots serve as reservoirs in which food is stored for future consumption by the plant. Aerial Roots.—Some plants, like the Ivy, climb by means of adventitious roots which, in place of dipping down into the soil, adhere to the surface of a tree, wall, or rock. Roots above the surface of the soil are described as being aerial roots. CHAPTER III VEGETATIVE SHOOT—LEAVES A SHOOT, in addition to possessing stems and leaves, may bear flowers. If we exclude the flowers, the remainder of the shoot may be spoken of as constituting the vegetative shoot. For the present, flowers will not be considered. By making marks in Indian ink at equal distances along the stem, it is easily shown that a stem grows in length only near its tip. We can see this apical growth even more simply by observing the leaves constituting a growing bud. At first they are packed close together, but as the terminal part of the stem elongates they become separated by distinct intervals along the latter (figs. 6-11). Thus the youngest part of a single stem is nearest its tip, and the oldest part is that portion which is nearest its base. If we pull the leaves from an actively growing bud of a Wallflower or Sunflower, we see that the external leaves of the bud are inserted lower down the stem than the internal leaves, and are larger than the latter; and the inmost leaves are the smallest, and are inserted nearest the actual end of the stem. Thus eaves arise* only in the region of the apex of a stem and appear in acropetal succession—that is, the youngest leaf is the one which is nearest the end of the stem. As the tip of the stem elongates, the leaves are, so to speak, left behind, and continue to grow till they attain their full size. The leaves are attached laterally to the stem at certain points, which are termed nodes. These points of attachment are separated by portions of the stem—the internodes—which are devoid of leaves but connect the successive nodes (see figs. 4, 5). * The leaves arise as external lumps on the side of the stem, and are thus exogenous in origin. 9 10 VEGETATIVE SHOOT If the young part of a shoot be examined, it will be found that in the angle between the upper face of each leaf and the stem there is a bud (fig. 3 4). This angle is described as the axil of the leaf Thus we may say that a Jateral bud* arises on a stem in the axil of every leaf. These buds are the beginnings of the lateral shoots or branches, and can develop into shoots (fig. 3 ii.). We see, therefore, that lateral shoots arise in the axils of leaves—in other words, the dvanching of the an eS AP II Figs. 6-11.—Development of bud of Hazel. (After Dennert.) shoot ts axillary. A shoot possessing an unbranched stem is described as simple (figs. 3, 4, the two left-hand drawings), but when the stem is branched, the shoot is said to be compound (figs. 3, 4, the right-hand drawing). Normal buds, then, are terminal or axillary. A bud does not necessarily develop at once into a branch. It may remain in a resting or dormant condition, and is then described as a vesting-bud, to distinguish it from an active bud. * The bud appears as an external outgrowth of the stem ; it is exogemouts, LEAVES 11 Adventitious Shoots.—Lateral shoots may arise on some flowering plants in places other than the axils of leaves. Such shoots are said to be adventitious. For instance, adventitious shoots may burst’ out from the roots of Poplars, Rose-trees, Hazels, and raise themselves above the surface of the soil. Again, adventitious shoots may spring from cut fragments of Dandelion-roots, or from Begonia-leaves pegged down to produce cuttings. When young branches shoot out from older parts of tree-trunks they are often axillary branches, and their appearance is merely due to the sudden activity of resting-buds which were formed years before. But in the case of Willow-trees from which the upper shoots have been lopped, many entirely new lateral buds arise on the upper part of the trunk. These grow out to form branches which are adventitious, because they are not due to the de- velopment of resting axillary buds. In all these cases of adventitious branching the shoots produced have stems and leaves, and therefore are shoots. ARRANGEMENT OF THE LEAVES. The leaves are attached to the nodes of the stem. On the stems of some plants (e.g. Buttercup, Wallflower) no two leaves are inserted at the same level on a simple stem—that is, there is only one leaf at each node. This leaf-arrange- ment is described as alternate or, better still, as spzra/ (acyclic). On other stems two or more leaves are attached at the same level and at the same node of a stem. The leaf-arrangement is then described as whorled (cyclic), and the collection of leaves at each node constitutes a whorl. Whorled (Cyclic) Leaves.—In this leaf-arrangement the leaves at a single node are disposed in a very regular manner. They are inserted in such a way that the angular distance between each two adjacent leaves is the same. Thus, if there be two leaves at the node, they are inserted on the opposite sides of the stem (say the north and south sides), as in the Chickweed (fig. 43) and Dead Nettle; if there be four leaves, they are ranged like the four points of a compass (say N. S. E. W.); if there be three leaves at a node, each is separated from its neighbour ' 12 LEAVES by one-third of the circumference. The relative disposi- tion of the leaves at the different nodes is equally regular. In some cases the leaves at the successive nodes are exactly above one another (superposed), so that there are just as many rows of leaves along the stem (longitudinal rows) as there are leaves at each node—for instance, there will be two longitudinal rows of leaves if there are two leaves at each node. But on other stems with whorled leaves, the leaves at one node stand above the gaps midway between the leaves of the next lower or next higher node; thus the leaves at the successive nodes exactly alternate with one another. Consequently, the leaves of every second node will stand above one another. In this case there will be exactly twice as many longitudinal rows of leaves as there are leaves at a single node. For example, the Dead Nettle, the Chickweed (fig. 43), have two leaves at each node, but those at the successive nodes alternate so that there are four rows along the stems. Alternate or Spiral (Acyclic) Leaves.—When only one leaf stands at each node (fig. 12), the leaves are arranged in spirals, and not in circles or whorls. They form rows, and are ranged one above the other along the stem, as is the case with whorled leaves. Each leaf is separated from the one at the next node, either below or Fig: 4B hoo of Hl with} est above it, not only by a vari able distance along the stem, but also by a certain invariable angular distance round the stem. For example, on Grass-stems and most Hazel-stems LEAVES 13 there is one leaf at each node, and each leaf is inserted on the side exactly opposite to that on which the leaf at the next node is attached ; consequently we have to travel half-way round the stem (as well as go higher up) in order to reach the single leaf at the next higher node: the divergence, or angular distance, is described as being . Again, in some Hazel-shoots (fig. 12) we have to travel one-third of the way round the stem in passing from one leaf to its predecessor or successor, and .the divergence is said to be $. On the stems of the Oak, Red Currant, Pear, Poplar, Musk Rose, the divergence is 3. The consequence of this constancy of the divergence between the leaves of the successive nodes of a stem is that the above-mentioned longitudinal rows of leaves are formed. In the Grasses and most Hazel-shoots with 4 diver- gence, the leaves are ranged in two rows; in the Hazel-shoots with 4 divergence, in three rows; on Pear-trees, etc., with 2 divergence, in five rows. Thus in each case the numerator of the fraction denotes the number of longitudinal rows of leaves. And the numerator of the fraction represents the number of times it is necessary to travel round the stem in passing from one leaf on a stem to the next one vertically above it, at the same time touching all the leaves on the way thither. This gives us an easy method for determining the exact leaf- arrangement of a shoot. The commonest series are repre- sented by the fractions 4, 4, 2, 2, 3%. This series can be remembered with ease if we note that— I+1 2 I+2 aad 2+3 5 Possibly the most simple way to understand the ‘spiral method of arrangement of leaves is to look at the cone of a Pine- tree, or to remember that the leaves are distributed like the steps of a spiral staircase. Diagrams to represent the leaf-arrangement.—We can denote the method of arrangement of the leaves on a stem by a plan or map, representing a side view of the surface of the stem unrolled into one plane, much as we show the surface of the spherical earth with its two hemispheres extended on a single flat map. Or, on the other hand, we can for a moment imagine that a shoot is like a large bud, and that we are looking down 14 FOLIAGE-LEAVES on the top of ‘the stem. We then draw a plan such as would be seen in cutting across a bud, the outermost leaves being those which are inserted at the lowest level, and the innermost leaves being those which are nearest the apex. Thus the diagram represents a sort of ground plan of the leaves and Fig. 15. ; Fig, 16. stem. Figs. 13, 14, 15, 16, will explain this second method of representing leaf-arrangement by diagrams. Fig. 13 » represents whorled arrangement with two leaves in each whorl. Figs. 14, 15, 16, are diagrams of spirally-placed leaves with divergences of 4, 3, and 2 respectively. FOLIAGE-LEAVES. A complete type. of green leaf (fig. 17) consists of three parts: (i.) a flattened green d/ade or lamina (sp), which is the most conspicuous portion of the leaf; (ii.) a narrow, elongated stalk or petiole (st), which connects the blade with (iii.) the FOLIAGE-LEAVES 15 ‘expanded and flattened basal sheath, by which the leaf is attached to the stem. The sheath frequently bears two lateral outgrowths known as the stipules (nb). (i.) THE SHEATH. The sheath of a leaf may be well developed (e.g. Butter- cup, Carrot, Cowparsnip), but frequently it is not distin- guishable. The stipules (fig. 17 2) usually take the form of two flattened expansions of the leaf-sheath. They are parts of a single leaf. A leaf possessing stipules is described as stipulate; a leaf devoid of stipules is said to be exstpulate. Most frequently the stipules are small, and serve merely to protect the young grow- ing leaves of a bud: in which case they. drop off (¢g. Pear) or shrivel as they unfold from the bud. But the stipules may form good-sized green plates, which persist as long as the leaf -blade— e.g. Hawthorn (fig. 58 2), Pea (fig. 59 7), Violet. In the rhubarb-family, the two stipules of each leaf are replaced by a membranous pipe embracing that part of the stem which is: near the leaf. The leaf of a grass has a long tubular sheath which surrounds the stem, but aie pees is usually split down;one side. The leaf “""(aher Dennert.) possesses no stalk, so that the sheath is | directly continuous with the blade. At the junction of the blade and sheath a. small membranous plate—the Agule— stands out from the upper face of the leaf. (ii) STALK orn PETIOLE. The stalk varies in length: in fact, it may be entirely absent, in which case the leaf is said to be sessede. Generally the ‘stalk is attached to one end of the blade; rarely it is fixed to the lower face of the lamina, as in the garden Zropcolum (commonly, though incorrectly termed “ Nasturtium ”). 16 FOLIAGE-LEAVES (iii.) BLADE or LAMINA. The blades of foliage-leaves exhibit great diversities of form and size. In form the lamina is usually a flat expanded plate or ribbon-like structure ; but it exhibits all variations from the narrow needle of the Scotch Pine to the circular disk of Tropeolum. Its apex may be drawn out into a fine point or end bluntly, or even terminate in an indentation. The margin is even (entire) or uneven (toothed, saw-like, scalloped, etc.). Venation of the Lamina.— The substance of the blade is traversed by veins or nerves which frequently stand out more or less prominently. The arrangement of the veins f, may be grouped under two ES general headings—(i.) paraé- Wg lel-veining ; (ii) net-like vein- ing. In parallel-veined leaves a number of veins, approxi- mately equal in size, run side by side from the base of the lamina towards its tip. The veins are more or less parallel, Fig. 18.—Venation of Hazel leaf. and are connected bya limited (After Dennert.) number of smaller ones which join them at right angles. This type of venation is characteristic of Grasses, Lilies, and most other Monocotyledons. In net-veined leaves the finer veins are numerous, and form a complicated network (fig. 18). Most Dicotyledons have net-veined leaves. There are two sub-types of net-like venation—g7nnate and palmate veining. A lamina which is pimnately-veined (feather-veined) has a single main vein—the mid-rib — which traverses the centre of the blade, running from the base towards the apex; this mid-rib gives off from its two sides smaller veins, which are arranged much like the pinne of a feather—e.g. Hazel (fig. 18), Pear, Primrose. A fpalmately-veined leaf, in place of possessing a j FOLIAGE-LEAVES 17 single mid-rib, has several large main veins which radiate in various directions from the base of the lamina towards its margins—e.g. Mallow. Division of the Lamina.—The form of the lamina may be very simple, because all the spaces between the nerves are com- pletely occupied by leaf-substance—e.g. Pear, Hazel. Often, however, incisions of considerable depth proceed from the margin, thus tending to complicate the form of the lamina and to split it into smaller sub-divisions. The degree to which the leaf is divided into smaller parts varies ; for instance, the incisions are shallow in the Oak-leaf, but they are deep in the Buttercup-leaf. So long as the divisions do not reach the large nerves, the leaf is said to be simple (figs. 19-22, 24-26). VERS Figs. 19-23.—Division of pinnately-veined lamina. When the lamina is divided by incisions which reach the main ribs there is no longer one single lamina, but there exist a number of distinct leaflets, and the leaf is described | as compound (figs. 23, 27)—e.g. Rose, Pea (fig. 59), Clover. 24 25 26 27 NY wi sy | ‘ . ' NX ae Figs. 24-27.—Division of palmately-veined lamina. Since a compound leaf consists of a number of distinct leaflets attached to a common stalk, it may be asked why should we not term it a branch and describe the leaflets as leaves. Several reasons may be given which serve to show that a com- pound leaf is a single leaf, and is not a branch. B 18 SIMPLIFIED LEAVES (1) It does not arise in the axil of a leaf; on the contrary, it has a bud in its axil. (2) Often it possesses two stipules at the base of its stalk —e.g. Rose, Pea (fig. 59 7). (3) The leaflets do not necessarily arise in acropetal succes- sion on the stalk of the compound leaf, neither does the latter terminate in a bud. (4) The leaflets have no buds in their axils. {s A leaf is always lateral on an axis, but a leaflet may be terminal on a leaf-stalk—e.g. Rose. When the leaflets are ranged along the sides of an elongated stalk, the leaf is said to be pinnately-compound (fig. 23)—eg. Rose, Pea. On the other hand, when the leaflets spring from a single point at the summit of the stalk, the leaf is dzgttate (fig. 27)—e.g. Clover and Strawberry, with three leaflets (fig. 54), Horse-chestnut with about seven leaflets. SIMPLIFIED LEAVES. Some leaves are much simpler than the green foliage-leaves. They may be described as simplified leaves, and be arranged under four heads: Scales, Cotyledons, Prophylls, and Bracts. Usually they are not differentiated into sheath, stalk, and blade; frequently they represent merely parts of complete leaves. SCALES. Scales are small, simple leaves, usually with even (entire) margins. They possess little or no green colouring-matter, but are brownish or pale in colour. They are without stalks, and are attached to the stem by a relatively broad base. Scales occur upon parts of the stem which are above ground in the form of dud-scales, as in the Hazel and Oak, or quite apart from the buds, as in the Scotch Pine and Asparagus. But they are also present on subterranean stems, as in the Hyacinth, some Grasses, and Potato-tubers. Scales are therefore not defined by their position on the stem. A scale may represent the persistent base of a foliage-leaf, the upper portion of which has died away (as in some bulbs) ; in other cases the scales may be arranged in pairs, and are merely the stipules of leaves the blades of which never develop (as in the resting-buds of the Hazel) ; finally, some scales represent complete leaves (as in the bulb of a Lily). SIMPLIFIED LEAVES 19 COTYLEDONS. One characteristic of an ordinary Dicotyledon, the Bean for example (fig. 2), is that the first two leaves produced by the embryo are inserted opposite to each other on the primary axis, and in form they differ from the subsequently produced foliage-leaves. These two leaves are known as the cotyledons. [Frequently the cotyledons are termed seed-leaves, because they are found inside the seed. But this expression seed-leaves is a bad one, because it seems to suggest that the seed bears cotyledons, whereas it is to the stem of the embryo inside the seed that these leaves belong.] Cotyledons are simple leaves, usually with margins devoid of any incisions; only very rarely do they possess stipules or definite sheaths, though occasionally they have distinct stalks. When the seed germinates the cotyle- se. ne dons may remain hidden in i the soil, in which case they are not green in colour—e.g. Bean ; but in other cases p the cotyledons emerge (fig. 4) from the soil and become 7 green—e.g. Beech, Sycamore, i Mustard. He PL Sai a ee Opposed to the Dicotyle- eee Oe. rene dons are Monocotyledons, whose embryos possess only one cotyledon each. That is to say, the first leaf formed by the embryo is attached to the axis at a lower level than any other leaf. We may select the grain of the Wheat, for the purpose of examining a Monocotyledonous embryo. Structure of a grain of Wheat (fig. 28). As will be shown later, the grain of wheat is not a seed, but is a fruit with a single seed which occupies the whole of its cavity. The grain is smooth and convex on the one side, and deeply furrowed down the middle of the other side. Its main mass is formed by a substance termed the endosperm (2). The embryo is a small body placed at the bottom corner of this endosperm. Looking at the convex surface of the grain from the outside, there is a pale patch which indicates the position of the embryo. The latter is rather ‘ \ \ + mri iim MM 20 SIMPLIFIED LEAVES complicated in form. The root-system consists of a short primary root (7), with a peculiar sheath, and several small lateral roots. The axis (f/) above the primary root bears a number of alternate sheathing-leaves. But one character- istic feature of the embryo of this and other grassés is that, attached to the hypocotyl, is a shield-like outgrowth— the scutel/um (sc)—which separates the rest of the embryo from the endosperm. Botanists are not agreed as to which portion of the embryo represents the cotyledon. There are the three following views:—(1) The scutellum is the cotyledon, (2) The first sheathing-leaf and the scutellum together constitute the cotyledon. (3) The scutellum is merely ‘a “subsidiary outgrowth” (emergence) of the hypo- cotyl: and the first sheathing-leaf represents the cotyledon. Comparison between a Wheat-grain and a Bean-seed and their Germination. GRAIN OF WHEAT. 1. Is a fruit which contains one seed. The wall is composed of the fruit-wall (pericarp), together with a very thin testa, which can be distin- guished only with the help of a compound microscope.* 2. The space within the testa is occupied by endosperm and an embryo. The seed is consequently described as exdospermic. 3. Embryo has one cotyledon. 4. In germination. (a) The endosperm shrivels as the seedling develops : it is the food-supply of the embryo. The scutellum is the sucking-organ which absorbs nutriment for the benefit of the young plant. (4) The main root forces its way through a peculiar root- sheath. (c) The main root soon ceases to grow, and adventitious roots arise on the stem. BEAN-SEED. 1. Is a seed. Its wall is formed by the thick testa only. z. The space within the testa is occupied by an embryo only. There isno endosperm. The seed is said to be 20n-endospermtc. 3. Embryo has two cotyledons. 4. In germination. (a) The cotyledons shrivel as the seedling develops. They contain the food- supply of the embryo. (4) The root has no peculiar root-sheath. (c) The main root continues to develop and __ produces acropetal lateral roots. * Recent investigations tend to show that, in reality, the testa is entirely destroyed before the grain is ripe, SIMPLIFIED LEAVES 21 PROPHYLLS or PROPHYLLA. In many Dicotyledons the first two, therefore the lowest two, leaves borne on each branch are small and scale-like. These two simple leaves—the rophylls—are inserted on opposite faces, the right and left sides of the branch. In Mono- cotyledons, on the other hand, there is only one of these simple leaves at the base of the branch, and it is inserted alone on the upper face of the branch-—that is, on the face which is directed towards the main axis. We can easily re- member these facts if we recollect that in Dicotyledons and Monocotyledons the leaves first formed on any stem are -usually simplified. The first leaves of the primary stem are cotyledons ; those of a lateral stem are prophylls. In Dicoty- ledons the primary axis has two cotyledons, the branch two prophylls ; in Monocotyledons the primary axis possesses one cotyledon, the branch one prophyll. BRACTS. Often the leaves situated on that region of the stem which bears the flowers are simpler, and usually smaller, than the foliage -leaves of the same plant. These simplified leaves borne in the region of the flowering part of the shoot are termed bracts —e.g.. Daisy, Bluebell, Hyacinth. In the majority of cases, bracts are small, without stalks, and attached by broad bases; their margins tend to be entire. Bracts may assume the form of small scales, as, for example, in the case of the glumes of grasses (fig. 231), the chaffy bracts of the Sunflower (fig. 208). Exceptionally large sheathing bracts, which enclose the whole inflorescence, occur in the Avum, also in the Snowdrop, and are termed Sfathes (fig. 226). CONSIDERATIONS WITH REGARD TO SCALES, PROPHYLLS, COTYLEDONS, AND BRACTS. The remarks in the few preceding paragraphs render it obvious that scales are defined by their form, and are not confined to any particular regions of the shoot ; but the other three varieties of simplified leaves occupy certain definite positions on the plant, and are defined as well by their position as by their simple forms. That they all represent true leaves is proved by the following considerations: — (i.) They are lateral appendages of the stem arranged like foliage-leaves, 22 BUDS and have buds in their axils. Often it is an easy matter to cause these axillary buds to develop into branches; for in- stance, if we nip off the stem of a Scarlet Runner just above the points of insertion of the cotyledons, the buds in the axils of the latter will shoot out and become branches. (ii.) In many plants transitions from foliage-leaves to bracts (eg. Rose, Christmas Rose), or to scales (e.g. buds of the Horse- chestnuts), or even to cotyledons, occur. (iii.) It is possible to cause foliage-leaves to appear,in place of scales; for ex- ample, some stems (e.g. Potato-tubers), which are normally subterranean, when caused to develop above ground, pro- duce foliage-leaves instead of small scales. BUDS. Astivation is the term applied to denote the arrangement of the different leaves of a bud with reference to one another. In the bud the leaves forming a single whorl or spiral may not be in contact, in which case the estivation is said to be 29 30 31 Figs. 29-37-—Diagrams of Vernation. In figs. 32-37 the shaded face of leaf is the upper face. The leaves are transversely cut. open. When their edges just touch, without overlapping, the zstivation is va/vate. Finally, when the leaves overlap the sestivation is zmbricate. BUDS 23 Vernation is the term applied to denote the manner in which each single leaf is packed in the bud. Each leaf may be flat or plane (figs. 29, 32). In some cases the leaf is folded in various ways along the courses of the chief veins. The two halves of the lamina may be simply fo/ded together mene the mid-rib, like two pages of a book (figs. 30, 33); or there may be a number of folds (fig. 34) along several of the large | veins, especially in leaves with parallel venation (e.g. many grasses) and with palmate venation, so that the young leaf reminds us of a closed fan or a i. pleated garment, Fis a8—Uorling at mves (uf of bd of Pe, In other instances the leaf is vo//ed from side to side. Each half of the lamina may be rolled towards the middle line of the upper face of the leaf, as in the Pear (figs. 31, 35, 38), or towards the middle line of the lower face (fig. 36). Occasionally the whole lamina is rolled sideways in one direction (fig. 37). Finally, the leaf may be cozled from the apex of the leaf towards the base, like a watch-spring. CHAPTER IV STEM AND SHOOT DEFINITE AND INDEFINITE GROWTH IN LENGTH. An ordinary stem of a flowering plant elongates solely by means of growth at its apex. The apex may continue to grow for a long period, so that the stem will bear many leaves and lateral buds; such a stem is said to be unlimited or zvdefinite 4° 39 Fig. 39.—A_ dwarf-shoot of Pine, in axil of scale (sc). ° Fig. 40.—Vertical section of ditto. in its growth. On the other hand, the apex may soon cease to grow, so that the stem attains only a limited or definite length. The Scotch Pine (fig. 62) has shoots which exhibit both these methods ‘of growth. The main trunk and con- spicuous branches are of indefinite growth, and bear leaves only in the form of scales ; they constitute the so-called long-shoots. In the axils of most of the scales on the long-shoots there arise lateral dwarf-shoots ‘(fig. 39). Each dwarf-shoot consists of a short definite stem, bearing just below its apex two needle-like green foliage- leaves (/), and below these a number of scale-leaves (s): the apex (a) of the stem lies between the two needles (fig. 40). Stem or axes of different orders (fig. 41).—A stem is an axis bearing leaves. This definition gives us no means of stating simply whether the stem be a main stem or a lateral one: hence it is advisable to adopt some terms by which we can explain to which stem we are alluding. .The main stem (1.) is described as an axis (stem) of the first order, or .as the primary axis. A lateral axis (11.) 24 STEM 25 arising on the primary stem is termed an axis of the second order, or a secondary axis. A lateral axis (11I.) arising on a secondary axis is an axis of the third order, or a tertiary axis ; and so on. Formation of false-stems or sym- podia.—A simple stem being un- branched obviously must be an axis 2 of the first, second, or third, etc. order. Frequently, branched stems are formed which, at first sight, seem to be simple ; this is particularly the: ~ case in plants possessing stems of definite growth. The formation of such a falsely simple stem—a sympodium—may be illustrated by considering the growth | of a grass which lives for several years and possesses a sub- terranean shoot-system. Following out the development of a horizontal under-ground stem of a grass, it will be seen that the end of the stem eventually bends out of the soil, becomes erect, and terminates in an in- florescence. But the base of the erect portion of this stem produces a bud which grows for a certain distance in the soil and presents the false appear- ance of being a continua- tion of the original stem. ° This lateral axis in turn bends out of the soil and produces flowers as did the first stem. A third axis arises on the second lateral axis and behaves in exactly the same manner Fig. 42.—Method a aro of a perennial as its predecessors. Fig. a Tass. . . 42 is a diagram of a grass which is supposed tg be flowering at the present time (in summer). A year ago, axis I. bore flowers (which are now invisible), and it also possessed’ a leafy branch (11), the Fig. 4x. 26 STEM termination of which had emerged from the soil. This year, axis 11. is flowering, and its branch (axis 111.) has just emerged from the soil with its foliage-leaves, and will next year terminate in an inflorescence. Axis 111. has a branch of its own, (axis Iv.), which next year will push above the soil and assume the present condition of axis 111., and in the second year after will flower. It will thus be seen that the creeping subterranean axis is not a true axis, but is composed of the subterranean portions of axes L, U., 11., IV., apparently strung together end to end. Each true axis is roughly L-shaped, and the sym- podium is made up of the bases of successive Ls. Some of our trees, especially Willows, Elms, Limes, Beeches, have sympodial branches, which are produced in a slightly different manner. In these trees the terminal buds of the branches often die in autumn, and in the following year the highest axillary bud on each shoot grows out and behaves as if it were the true terminal bud. Again, in the Hazel occasionally an axillary inflorescence arises close to the apex of a shoot, and as it develops it causes the terminal bud to die and drop off (see fig. 131). ARRANGEMENT OF BRANCHES. So far as we have considered a flowering plant, we have found that every leaf has a bud in its axil. An axillary bud is simply a small lateral shoot which may develop into a branch. If all the axillary buds of a plant were to grow out, the branches would be arranged on exactly the same plan as the leaves (z.e. in whorls or in spirals). But many leaves have no branches in their axils; this is due to the fact that, though the buds are present they remain inactive. Thus we may range buds under two heads: those which are active or growing, and those which are inactive or vesting. The disposition of branches on a stem depends, therefore, not only on the arrangement of the leaves, but also upon the behaviour of the axillary buds. Racemose branching.— When a stem grows strongly and produces a considerable number of branches which remain smaller than itself, the branching is said to be racemose (fig. 4). Cymose branching.—When a stem grows only for a limited time and produces only a few branches which subsequently develop more vigorously than the stem which bears them, the branching is said to be cymose (fig. 43). STEM 27 HERBACEOUS AND WOODY STEMS. There is considerable variety in the toughness, consistence, and longevity of stems. A stem may be soft and relatively short-lived: in which case it is Ag said to be herbaceous. A plant, the above-ground stems of which are invariably her- baceous, is described as a herb, With the exception of our herbaceous climbers (e.g. % Convolvulus) nearly all British herbs are plants of low stature, like the Buttercup and Prim- rose. Opposed to herbs are trees and shrubs whose stems are hard and woody, and cap- able of existing for consider- able periods. with a transverse-zygomorphic, flower. The signs 6, 9, %, denote respectively staminate, carpellary, and monoclinous flowers. The capital letters K C (P), A and G represent the calyx, corolla (perianth), andrcecium, and gynecium. The number placed immediately after each capital letter shows the number of leaves in that particular whorl or spiral. If the gynecium be syncarpous, its number is enclosed in brackets, otherwise the number is not in brackets ; if the ovary be inferior, a hori- zontal line is drawn above its number, if it be superior the line is placed below the number. The sign o denotes that more than twelve floral leaves are present, it therefore means numerous. Floral formula of the % flower of the Buttercup, ® K5 C5 Aco Goo Floral formula of the § flower of the Pea, ) K5 C5 A5+5 Gl Floral formula of the ¢ flower of the Hazel, @® PO A4? GO Floral formula of the ? flower of the Hazel, @® PO (?) AO G(2) SHAPE OF THE RECEPTACLE. Hypogynous flowers (fig. 105).—In some simple flowers the portion of the stem which bears the floral leaves—that is, the receptacle—is distinctly elongated (e.g. Scotch Pine, figs. 63, 65; Buttercup, fig. 61). More frequently the internodes of the receptacle are much shorter, though the flower-stalk terminates in a rounded convex end (e.g. Wallflower, fig. 156; Poppy, fig. 183; Violet, fig. 158; Primrose, fig. 187). In such flowers the carpels occupy not only the most central, but also the highest, position; and petals and sepals are inserted at successively lower levels. The flower is then said to be hypogynous, and the gyneecium is superior. SHAPE OF THE RECEPTACLE 75 Perigynous flowers (fig. 106).—The end of the flower-stalk of some other flowers is hollowed out to form a basin-like or deep urn-like concave receptacle. The carpels are attached to the 105 106 107 Figs. 105-107.—Vertical sections of flowers, showing the shape of the receptacle (+) which is shaded black : ow=ovary. t base (e.g. Cherry, fig. 177), to an outgrowth from the base (e.g. Blackberry, fig. 173), or to the sides and base (e.g. Rose, fig. 168), of the concavity, whilst the sepals and petals are inserted on its rim. The flower is then serigynous; the gynecium is still described as superior. : Epigynous flowers (fig. 107).—Finally, there are flowers possessing a receptacle which is hollowed, as in the perigynous flowers, and the carpels are not only concealed in the concavity thus formed, but they are actually fused with and coherent to its sides. It thus becomes impossible to separate the wall of the ovary (or ovaries) from the receptacle, and the sepals and petals appear as if they were inserted upon the ovary (or ovaries). The flower is then described as epigynous. The gynzecium is, in this case, said to be znferior (e.g. Heracleum, fig. 183; Daisy-family, figs. 202, 209, 211; Honeysuckle, fig. 199; Daffodil, fig. 215). It will be seen that the wall of an inferior ovary really consists of portions of the carpels and of the receptacle. Other peculiarities of insertion.—In hypogynous, perigynous, and epigynous flowers, frequently the stamens are attached to the petals (e.g. Primrose, Dead Nettle, Daisy-family) ; they are then said to be efipetafous. When the stamens are inserted on the perianth-leaves they are described as being epiphyllous 76 ARRANGEMENT OF FLORAL LEAVES (fig. 213). In the Orchids the stamens and style combine to form a central column. Disk.—Frequently the receptacle of a flower has upon it certain subsidiary outgrowths, which collectively form the asf. The disk may take the form of a whorl of two or more little swellings (e.g. Geranium, Chickweed) or scales; or it may be in the form of a single horse-shoe-like or ring-like outgrowth at the base of the style or stamens (e.g. Daisy-family), or may be a lining to the concave receptacle (¢.g. Rose). Very frequently the disk secretes honey: in which case it is a nectary or a collection of nectaries. CHAPTER XI NECTARIES—POLLINATION NECTARIES. ArT the base of each petal of the Buttercup there is a small pit, the lining of which pours out sugar, and is termed a mecfary or honey-gland. The petals of the Winter Aconite and Christmas Rose assume the form of tubes, which likewise excrete sugar, and are thus nectaries. The flower of the Monkshood (figs. 151, 152) has only two nectaries, which are attached by long stalks and represent portions of two posterior petals (2), which are concealed beneath the large blue cowl-like posterior sepal. The two anterior stamens of the Violet or Pansy (fig. 158) send narrow band-like processes (a) into the spur of the anterior petal; on each of these processes is a spot which denotes the location of the honey-gland. Thus, in the Pansy or Violet, we can distinguish between the nectaries which are portions of the stamens and make the honey, and the xectar- receptacle which is the spur of the anterior petal and receives the sugar manufactured by the nectaries. In the Marsh Mari- gold, and in Avum, parts of the gynzecium act as honey-glands ; whilst in the Mallow the five nectaries are on the five sepals (fig. 161 2). In fact, sepals, petals, stamens, or carpels may be partially or wholly modified to excrete sugar. In other cases, however, the nectaries do not represent portions of the floral leaves, but are parts of the receptacle. For instance, in the flower of the Wallflower (figs. 88, 156 ~) there are two honey- glands, each being in the form of a green ring-shaped out- growth round the base of one of the short stamens; the two lateral saccate sepals act as honey-receptacles to receive the sugar overflowing from the two nectaries which lie above them. POLLINATION. Under certain circumstances the ovules of a plant change into seeds ; in fact, seeds cannot be formed excepting from ovules 77 78 CROSS-POLLINATION Consequently, flowers which possess stamens, but have no carpels, do not bear seeds. Whereas flowers devoid of stamens, but endowed with carpels, may produce seed. Experiment has shown that the ovules do not change into seeds unless pollen grains have previously been conveyed on to the stigma (or, in Gymnosperms, into the micropyle of the ovule). The pollen in some way exerts a fertilising influence on the ovule. The transference of pollen from an anther to the receptive part of the carpel of a flower is referred to under the term pollination. Cross- Pollination and Self-Pollination.—The simplest method of pollination is the transference of the pollen from the anther to the stigma of the same flower ; this is described as self-pollination, and the flower is said to be selfpollinated. When, on the other hand, the stigma of a flower receives pollen from the flower of another individual-plant of the same kind, it is, said to be cross-pollinated. Lastly, pollen may be transferred from one flower on to the stigma of another flower of the same individual-plant; this is obviously a stage between cross-pollina- tion and self-pollination, but there is no simple word or term in use by which to distinguish it. CROSS-POLLINATION. It has been proved that in many species of plants cross- pollination leads either to larger crops ef seeds, or to the pro- duction of seeds which are better in quality than is the case when the same plants are self-pollinated. Accordingly, many arrangements exist in flowers which are calculated to hinder self- pollination and facilitate the more invigorating cross- pollination. Arrangements for hindering Self-pollination :— (i.) Sometimes ¢he stamens and carpels do not occur in the same flowers, consequently the pollen must be conveyed from one flower to another. The stamen-bearing (staminate) and carpel-bearing (carpellary) flowers may occur on the same individual-plant, as in the Hazel, Oak, and Pine. Or the two kinds of flowers may be on different individual-plants, as in the Willows, in which case the stamens are borne on one tree and the carpels on another tree. (ii.) Sometimes the stamens and carpels in one flower ripen at different times; the consequence is that, though the WIND-POLLINATED FLOWERS 79 flower possesses both stamens and carpels, the pollen and the stigmas are not ready for pollination at the same time. When the stamens shed their pollen before the stigma is ready to receive it, thé flower is said to be pvoterandrous (e.g. Daisy- family, Mallow). But when the stigma is ripe before the anthers are able to dehisce, the flower is described as pro- lerogynous. (iti.) Sometimes the pollen has no fertilising effect on the ovules of the same flower, so that when the stigma receives pollen from the same flower no seeds result (e.g. some Orchids). (iv.) Zhe. relative arrangement of the parts of the flower, in some cases, prevents the pollen reaching the stigma of the same flower (see Pansy, on page 129; also see the long-styled form of Primrose, on page 150). Cross-pollination by the aid of the wind—Wind-pollinated flowers.—In the case of ordinary flowering plants with flowers raised above ground or above the water, it is necessary for pollen to be transported through the air if the flowers are to be cross-pollinated. The pollen has no power to move unaided, only rarely does the plant itself assist by throwing the pollen violently (as in the Stinging Nettle); so that the pollen is necessarily conveyed from one plant to another by the aid of the wind or by the agency of animals. Flowers which are cross-pollinated by the aid of the wind are described as wnd- pollinated flowers. Flowers which are cross-pollinated by the agency of animals are animalfollinated: in Britain the only animals which are of importance in effecting the cross-pollination of flowers are insects: hence we speak of zwsect-pollinated flowers. As examples of wind-pollinated flowers, we may mention Hazels, Poplars, and Grasses (see pages 109-112, 182-184). In regard to these wind-pollinated flowers, it will be noted that : (i.) ‘They are small, inconspicuous, and unscented. (ii.) They have no nectaries. (iii.) Their pollen is powdery, and not sticky. (iv.) The anthers are attached to long filaments, and hang freely out of the flowers, or are arranged in easily movable inflorescences, so that the pollen is readily, shaken out by a gentle breeze. (v.) The stigmas are well-developed, and often feathery or thread-like, so that a large surface is exposed to receive any pollen blown thither by the wind. 80 CROSS-POLLINATION (vi.) Usually a large amount of pollen is produced. These characters serve to illustrate the general peculiarities of wind- -pollinated flowers. The wind-pollinated flowers of the Pine differ in that the pollen is blown on to the open carpels, but here the open crevices of the carpellary cone must be regarded as exposing the large surface to receive the pollen. Cross-pollination by the agency of insects — Insect-pol- linated flowers.—The Buttercup, Wallflower, Poppy, Pea, and Hyacinth all possess flowers which are cross-pollinated by the agency of insects. They serve to illustrate the general features of insect-pollinated flowers. (i.) They are brightly coloured or scented. (ii.) They usually possess nectaries, for the sake of whose honey insects visit them; occasionally (e.g. Poppy, Potato) in- sect-pollinated flowers do not manufacture honey, but supply their insect-visitors with food in the form of pollen. (iii.) The pollen-grains, in place of being powdery, are usually sticky, so that they adhere to the bodies of insects. (iv.) There is a certain correspondence between the positions of the anthers and the stigmas of the flowers. (v.) The stigma is not feathery or pencil-like, but, as a rule, is relatively small. These general statements are liable to exceptions; some insect-pollinated flowers are inconspicuous, and, so far as we can smell, are also scentless (e.g. Virginia Creeper). Insect- pollinated flowers have one advantage over wind-pollinated flowers ; they are pollinated by agents which move in definite directions—namely, from flower to flower. Wind-pollinated flowers are pollinated by the wind, which blows the pollen in any direction ; so that for every pollen-grain which reaches the flower of another individual-plant of the same kind, millions of other pollen-grains fall to the ground and are wasted. The insect-pollinated flower can afford to manufacture less pollen, and is more economical than a flower pollinated by the aid of the wind. The various colours and scents of flowers not only serve to attract insects, but they assist the insect in identifying the flower it wishes to visit. For example, we often see a bee confining its visits to one kind of plant—say a Poppy—during the whole of a morning. The fact that honey is sipped by insects visiting the flowers, together with the fact that wind- INSECT -POLLINATED FLOWERS 81 pollinated flowers have no nectaries, denotes that the nectaries serve to entice insects. The insects which visit flowers in order to obtain honey or pollen, belong to the families of the Beetles, Flies, Bees (in- cluding Wasps and Humble-bees), and Butterflies (with Moths). The majority of Flies and Beetles have very short tongues, and are not intelligent, so that they can only obtain such honey as is easily accessible ; the hover-flies form an exception to this rule, for they possess long tongues. The Bee-family provides the most important pollinating insect-agents; the simplest members have only short tongues; but many species of bees and wasps are clever, and possess long tongues, consequently they are able to discover and obtain honey which is carefully concealed and deeply placed. Finally, many Butterflies and Moths, with tongues even longer than those of humble-bees, can reach honey which is so deeply placed at the bottom of long tubes as to be inaccessible to the latter insects. We find that flowers of different shapes and tints do not receive equal attention from all these families of insects. Flowers like those of the Parsley-family, with freely-exposed honey (fig. 183), or the Buttercup, with honey scarcely con- cealed (fig. 61), receive relatively more visits from the short- tongued insects— flies and beetles—than do flowers with deeply-concealed honey (e.g. Geranium, fig. 165). Opposed to these flowers which are suited to the requirements of many kinds of insect-visitors are others which are specially adapted to receive certain particular classes of insects. The flowers of the Pea, Vetch, Clover, and Violet have their honey so well concealed that only clever insects with tolerably long tongues can reach the nectaries (figs. 96, 158); they are pollinated by the agency of bees, and are specially adapted to receive their visits, and may therefore be termed “ Bee-flowers.” The Monkshood (fig. 151) and Foxglove (fig. 193) are similarly “Humble-bee flowers” (see pages 120, 157). Finally, Pinks and the Honeysuckle are adapted to receive Butterflies and Moths respectively: their honey is not fully accessible to bees. Comparing the actinomorphic flowers of the Buttercup with the zygomorphic “ Bee-flowers” mentioned, it will be noted that the buttercup-flower may be entered from any side, and the visiting insect may crawl about in the flower and receive F 82 SELF - POLLINATION pollen on various parts of its body. On the contrary, the “ Bee-flower” is so constructed that its honey cannot be obtained unless the insect visits in a certain special manner ; the consequence is that the visiting insect receives pollen on a certain definite region of its body, and may unerringly convey that pollen to the stigma of the flower next visited. For instance, in the pea-flower it is the under-surface of the bee’s body which comes into contact with the pollen and stigma; in the Foxglove, it is the back of the humble-bee which is pollen-dusted and meets with the stigma. This ar- rangement in these “ Bee-flowers,” therefore, not only allows the flower to economise in pollen, but it also places the pollen and honey in a position of greater safety in regard to the injurious action of rain and the inroads of marauding insects. For further illustrations, refer to Ranunculacee (p. 121), Papilionaceze (p. 138), Labiate (p. 155), Scrophulariacez (p. 157), Caprifoliaceze (p. 160), Araceze (p. 180). SELF-POLLINATION. Although in the case of many plants cross-pollination leads. to the production of better seeds, or more seeds, than self- pollination, yet some plants produce quite as many seeds, and those of as good quality, by self-pollination as by cross- pollination. Cross-pollination has this advantage over self- pollination, that it frequently affords a better crop of seeds. But self-pollination is superior in one respect, it is easily secured and rendered certain: the pollen simply has to come into contact with a stigma which is ready and close at hand. The self-pollinated plant is not dependent on the presence of another individual-plant of the same kind in the im- mediate neighbourhood: furthermore, it neither demands the attendance of special insects nor the influence of wind in a certain direction to carry the pollen to another individual. Many flowers are self-pollinated, either spontaneously or by the agency of insects. Insects wandering over the Buttercup- flower frequently effect self-pollination. In MMalva rotundifolia (see page 134), and in some members of the Daisy-family, the stigmas curl down until they reach the pollen-laden anthers, so that the flower spontaneously pollinates itself. The flower of the Poor-man’s Weather-glass (Azagadlis), if it SELF - POLLINATION 83 be not cross-pollinated within the first three days, remains per- manently closed, and its anthers, coming into contact with the stigma, effect self-pollination. The Pansy (see page 129) has two kinds of flowers, the large variegated ones, which are cross-pollinated, and smaller ones, similar in shape, which remain closed and pollinate themselves. Finally, the Violet and the Woodsorrel, in addition to possessing their familiar conspicuous flowers, which are cross-pollinated, also have minute green and bud-like flowers of quite different form. These latter never open: they are peculiar self-pollinating or cleistogamic flowers. CHAPTER XII OVULE—FERTILISATION—-SEED—FRUIT OVULE. Aw ovule (figs. 108, 111) is a more or less egg-shaped body attached to the placenta by means of a stalk—the fumicle (f). The main body of the ovule consists of a central egg-shaped mass — the mucellus — = we ri which is surrounded by one or two coats — the integuments (in). Each integument is attached by its base to the nucellus, but elsewhere it surrounds the nucellus like a narrow- mouthed bag, which is open at the top. The opening at the top of the % integument or integu- ments is the *mucropyle (m); it allows free com- munication between the ; nucellus and the chamber Figs. 108-110.—Ovules. Figs. r11-r13.—Vertical sections through ovules. of the ovary. In the nucellus itself, near the micropyle, there is a minute clear space. This is in reality a closed bladder, and is termed the emédryo-sac. There are three common types of ovules, whose forms are best explained by the figures given. (1) An orthotropous ovule is one in which the stalk (funicle) is in the same straight line as the straight nucellus (figs. 108, 111). (2) An anatropous ovule is one in which the nucellus itself is straight, but is inverted, and consequently appears to be attached by its side 84 OVULE 85 to the funicle (figs. 109, 112). (3) A campylotropous ovule is one in which the nucellus is itself curved; often it is kidney- shaped (figs. 110, 113). FERTILISATION AND CHANGES IN THE OVULE. When a healthy pollen-grain reaches a suitable stigma (fig. 114 sg) it germinates by sending a slender tube (7) down the style. The end of this pollen-tube eventually enters the micropyle (#), and comes into contact with the nucellus close to the top of the embryo-sac (es).* The consequence of fertilisation is that the ovule grows and becomes a seed (compare figs. 114 and 115). The most important change in the ovule is that a minute new plant—the embryo— develops inside the embryo-sac. The embryo-sac grows and becomes, wholly ar or partially, filled with endosperm, which surrounds the embryo. This endosperm may be present - still in the seed, and : \ SO 4 i ‘ Fig. 114.—Vertical section through a carpel and an anatro- pous ovule, showing the pollen- tube entering the micropyle. 158). the seed is said to be exdospermic —eg. Grass and Violet (figs. 118, Or the endosperm formed in the ovule may be gradually absorbed by the growing embryo, so that in the ripe seed there remains no trace of it: the seed is then said to be xon-endosper- mic—e.g. Bean and Wallflower (fig. 116). In most flowering plants, whilst the em- bryo-sac, the contained endosperm, and the embryo are grow- Fig. 115.—Vertical sec- tion through a fruit of the Buttercup, with one anatropous seed: per = pericarp; ¢s=testa ; end= endosperm ; e76=embryo. * This process can only be followed properly by the aid of a compound microscope. In a few Angiosperms the pollen-tube does not-enter by the micropyle, but pushes its way through the substance of the ovule till In the Pine and Gymnosperms the pollen- grain itself reaches the micropyle and then sends out a tube. it reaches the embryo-sac. 86 SEED ing, the nucellus is being absorbed by them, and no trace of it remains in the mature seed. In such cases the whole of the seed within the testa represents the embryo-sac and its contents. In some plants the nucellus is not entirely absorbed, but persists and forms an endosperm-like layer within the 116 117 118 Figs. 116-118.— Vertical sections of seeds: =scar on seed; m= micropyle; ¢, ¢s=testa; e=endosperm ; fs=perisperm; co, cof=cotyledon; ét=plumule; »=radicle. Fig. 116.— Wallflower. Fig. 117. — Stellaria, Fig. 118.—/ris. testa: this is termed the perisperm—e.g. Stellaria (fig. 117). The testa is formed by the growth and hardening of the integument or integuments, and the micropyle of the seed represents the micropyle of the ovule. The funicle or stalk of the seed is identical with the funicle of the ovule. The subjoined table represents the corresponding parts in the ovule and seed :— OVULE = SEED (a) The contents of the embryo-sac= Embryo and Endosperm. (6) Nucellus . ; ‘ : = Perisperm. (c) Integuments . 3 s = Testa. (Zz) Micropyle ‘ ‘ : = Micropyle. (e) Funicle . : ‘ = Funicle. As examples of different types of seeds, the following may be cited as occurring in both Monocotyledons and Dicoty- ledons. (i.) Vo endosperm, no perisperm: Pea, Bean, Wallflower, Mustard, Pear, Apple, Hazel, Oak, and Chestnut (figs. 1, 116). FRUIT 37 (ii.) LEndosperm, but no perisperm: Buttercup, Violet, - Mallow, Castor Oil plant, and Grasses (fig. 118). (é (iii.) nee with scarcely a trace of endosperm: Stellaria g. 117). Outgrowths on Seeds.—The Violet and the Spurge have each a little lump near the micropyle (fig. 158). Many outgrowths are concerned with the scattering of the seed: for instance, the long silky hairs or the seeds of Poplars, Willows, and Willow-herbs, facilitate the dispersal of the seeds by the wind. FRUIT. The consequences of fertilisation are not confined to the ovules ; the carpels, and frequently other parts, of the flower are stimulated into vigorous growth, whereas the remaining parts SS y 7s = Fig. 119.—Fruit (legume) of Garden Pea, wither and fall off more speedily than they would have done had fertilisation not taken place. Zhat portion of a single flower which persists after fertilisation until the seeds are ripe is termed the fruit. There is one part of the flower which invariably persists — the ovary (or ovaries) -— this remains to form a protective case round the ripening seeds. Obviously the receptacle, or a portion of it, also remains. The corolla and stamens almost always wither soon and fall, consequently they play no part in the formation of the fruit ; whereas the calyx not infrequently persists. The Pea (or Bean, or Clover) may be selected as having one of the simplest of fruits. Its ovary, composed of one carpel, enlarges and becomes the familiar pea-pod (fig. 119), and constitutes the fruit inside which are the seeds. The 88: FRUIT Wallflower is slightly more complicated, in that the ovary is syncarpous, being composed of two carpels ; but in this flower, as in the Pea, it is the single ovary alone which, by its growth, gives rise to the single fruit (fig. 120). The Buttercup differs from the two preceding examples in that every flower has a number of separate ovaries, each representing one carpel. Each ovary enlarges and eventually encloses one seed (fig. 115). This flower thus gives place to a number of apocarpous seed- containing vessels, each similar to the pea-pod in so far as it consists of a single ripened carpel. We can, therefore, divide fruits into two groups: (i.) Simple fruits, produced by a single ovary which is composed of one (¢.g. Pea) or more carpels (e.g. Wallflower). (ii.) Compound fruits, produced by a number of apocarpous carpels in one flower (¢.g. Buttercup). Thus the fruit of a Buttercup is a compound fruit and consists of a number of simple fruits. The external wall of the chamber, or chambers, of a simple fruit is termed the pericarp. In the case of the simple fruits’ already mentioned, the pericarp is derived solely from the carpels ; it is the original wall of the ovary, which has grown. But if we consider a‘simple fruit derived from a single inferior ovary (e.g. Honeysuckle, Parsley, Yellow Flag, Orchid), the wall of the fruit represents part of the receptacle as well as portions of the carpels (see p. 75). Again, if we examine a ripened (fertilised) Dandelion-head (fig. 129), we shall see that it consists of a number of simple fruits. Every one of these is formed by the growth of a single inferior ovary, each of which belongs to a separate flower. This Dandelion-head is’ formed as a result of the fertilisation of a number of flowers. A fruit is formed from one flower, consequently the Dandelion-head’ is not a fruit, not even a compound fruit: it is a collection of fruits, or an infruct- escence. Comparing the behaviour of the pericarp.of the simple fruits of the Pea, Wallflower, Buttercup, and Dandelion, we see that the pericarp of the first two gapes open, or dehisces, when it is ripe, so that the carpels are freely open; whereas, on the contrary, the fruits of the last two do not open of their own accord. If we now examine the fruit of a Parsley-plant (or any Umbellifer), we note that it is formed by a single inferior, two- chambered ovary, composed of two carpels. When the fruit DEHISCENT FRUITS 89 is ripe the two carpels separate, but do not open. We may, therefore, divide simple fruits into three groups :— (1) Dehiscent fruits, the carpels of which open spontaneously. (2) Indehiscent fruits, the carpels of which remain closed, and, if syncarpous, do not separate. (3) Separating fruits, which are always syncarpous, and the carpels of which separate without opening. Again, comparing the fruits of the Pea, Wallflower, and Buttercup with those of the Honeysuckle, Gooseberry, and Currant, the first three have a thin, dy, hard or brittle pericarp ; whereas the second three possess a fresh, more or less fleshy or succulent pericarp. We may, therefore, further classify fruits into (1) dry fruits; (2) fleshy or succulent fruits. CLASSIFICATION OF SIMPLE FRUITS DEHISCENT FRUITS (Carpels opening) A. DRY (DEHISCENT). (i.) One-carpellary (composed of one carpel). (2) Opening down the ventral suture only, contain- ing one or more seeds (e.g. Pzeony, Winter- Aconite) = Follicle. (6) Opening down the two sutures, dorsal and ventral, and containing one or more seeds (e.g. Pea, Bean, Clover) = Legume. (ii.) Zwo-carpellary (composed of two carpels). (a) The two carpels separate as two valves, com- mencing from below upwards, and leave the seeds attached to a persistent frame-like parietal placenta which is termed the veplum. The chamber of the fruit may (¢.g. Crucifere) be divided into two chambers by a thin septum. which spans the space between the two parietal placente and persists in the fruit (fig. 120) ; or there may be no such septum, so that the ovary is one-chambered as is the fruit—e.g. Chelidonium (fig. 121). A number of seeds are present in the fruit = Siliqua. o Fig. 120.—Siliqua of Wallflower: ve = re- plum; /s = false sep- tum; o = seed; v = valve ; sg=stigma. Fig. 123. — Capsule of Foxglove dehiscing along two ventral sutures, and leaving the seeds attached to the axile placenta (/) ; sy=style ; cx=calyx. Fig. 121.—Siliqua of Chetidonium: r=re- plum. Fig. 124. — Capsule of Stellaria media dehiscing for a certain distance along three dorsal sutures and three ventral sutures; cx =calyx. Fig. 122.—Capsule of fris' dehiscing along three dorsal sutures (ds) ; vs= ventral suture; s=seed. Fig. 125. — Capsule of Anagallis dehiscing transversely: c=calyx ; s=seeds ; sg=style. Fig. 126. — Capsule of Poppy, . dehiscing by DEHISCENT FRUITS gI The siliqua is typically pod-like in shape, but a short broad form is often distinguished as a Srlicula (e.g. Shepherd’s Purse). (ii.) Zio or more carpels = Capsule. (a) Usually a dry dehiscent fruit formed by more than two combined carpels, dehisces /ong?- tudinally, and causes the pericarp to split into a number of valves. The splits may descend from the apex to the base of the fruit, or they may be merely confined to the upper part, in which case the separate valves are tooth-like (e.g. Cerastium, Primrose). Longitudinally dehiscing capsules are of four kinds. (a) Splitting along the ventral sutures. (B) Splitting along the dorsal sutures (e.g. Violet, fig. 158; Jris, -fig. 122). (y) Splitting along the ventral sutures, and separating from the partition walls of the capsule so as to leave the seeds attached to a middle axial column (e.g. Foxglove, fig. 123). (8) Splitting for a certain distance along both dorsal and ventral sutures, so that there are twice as many valves as there are carpels (especially in capsules with tooth-like dehiscence) (eg. Stellaria media, fig. 124). (4) Capsule with transverse dehiscence. The top of the capsule separates like a lid (e.g. Poor-man’s Weather-glass, fig. 125). (c) Capsule opening by a number of little holes or ores in the pericarp (e.g. Poppy, fig. 126). (Z) Capsule opening zrregularly. B. FLESHY (DEHISCENT). Some follicles are soft and green when they dehisce. The green succulent capsudes of the Balsam open violently, and fling their seeds to some distance. The capsule of the Woodsorrel has a soft pericarp, which splits open and allows the seeds to 92 INDEHISCENT FRUITS be violently ejected. The Horse-Chestnut capsules are succulent. The Walnut-fruit is not a nut: it is a stone-fruit, the outer fleshy layer of which bursts irregularly ; its so-called nut is therefore a “stone.” INDEHISCENT FRUITS Fig. 127.— Fig. 128.—Vertical sections of the Achene of drupe of Cherry: in the right-hand figure Sunflower. the fruit is cut vertically through the ventral suture (vs) and dorsal suture: in the left-hand figure the fruit is vertically cut ina plane at right angles to the pre- ceding one: s¢#=stony layer of pericarp ; zs=testa of seed ; cot=cotyledon. A. DRY (INDEHISCENT). One-Seeded. : (3 Pericarp stone-like (e.g. Hazel, fig. 138). = Nut. (2) Pericarp leathery, or hard skin-like. (4) Pericarp not adhering to the testa (e.g. Buttercup, fig. 115; Daisy-family, figs. 127, 212). = Achene. (8) Pericarp adhering closely to the testa, or the testa absent (e.g. Grains of Grasses, Wheat, fig. 28). = Caryopsis. B. FLESHY (INDEHISCENT). (1) The inmost layer of the pericarp is stone-like = Drupe. (a) The outer layer of the pericarp of a drupe is like a thin “skin,” the middle layer is usually soft and juicy, and the inmost layer is very hard FRUITS 93 and stone-like. The simplest drupes are composed of one carpel, with one stone enclosing one seed (¢g. Cherry, fig. 128, Plum, Apricot). The most complicated drupes are syncarpous, and have several stones, because the walls of each of the ovary- chambers has become separately changed into a stone with one seed inside it. It must be noted that the stones (e.g. Hawthorn) of stone- fruits are not seeds. A seed is produced from an ovule only, whereas the hard stone of a drupe is formed by a layer of the ovary-wall. (2) The pericarp is soft and fleshy throughout (e.g. Grape, Gooseberry, Currant, Orange, Cucum- ber) = Berry. (c) The fruit of the pear and apple is quite peculiar, and is termed a Pome. ‘The component five carpels are fused with the hollow receptacle by their outer faces, hence the gynzecium is inferior (fig. 178). The carpels are also com- bined with one another by their sides, but may be free towards their centres (ventral sutures), thus the gynzecium is only incom- pletely syncarpous (fig. 179). In the fruit a parchment-like membrane forms round each chamber, just as stones may form round the several chambers of a stone-fruit, whilst the rest of the pericarp grows vigorously and remains fleshy (figs. 180, 181). The seeds are contained in the five parchment-walled chambers (fig. 182). The pome is inter- mediate between a berry and a stone-fruit, also between a compound and a simple fruit. SEPARATING FRUITS (SCHIZOCARPS) These all possess more than one carpel. The constituent carpels separate as closed one-seeded chambers. (a) The fruit separates into as many closed one-seeded one- chambered parts as there are carpels. Each part represents a closed carpel, and is termed a mericarp 94 FRUITS (e.g. two-carpellary fruits of the Parsley-family, fig. . 185, and Sycamore) or a coceus (if the ovary consists of more than two carpels, eg. Mallow, fig. 164) / = Schizocarp. (6) The two-carpellary fruit is divided into four one-chambered one-seeded parts which separate as little “nuts.” Each “nut” therefore represents half a carpel (e.g. fruits of the Zabiate, and many Boraginacea). COMPOUND FRUITS. The compound fruit may possess a number of follicles (e.g. Peony, Winter Aconite), of achenes (¢.g. Buttercup, Rose, fig. 170, Strawberry, fig. 172), of drupes (e.g. Blackberry, fig. 175, Raspberry), insertéd on a receptacle. But obviously it cannot possess a number of silique or capsules, because these are always syncarpous fruits. DESCRIPTIONS OF COMPLETE FRUITS. The classification of fruits so far given refers only to the nature and behaviour of the pericarp. A few examples will illustrate the application of this classification to complete fruits. : (z) Pea: the fruit is simple (legume) and is the ripened carpel. (2) Honeysuckle :. the fruit is simple (berry), is the ripened inferior ovary, and therefore includes the receptacle. (3) Dandelion: the fruit is simple (achene), and consists of the ripened inferior ovary (carpels and receptacle) and pappus. (4) Raspberry: the fruit is compound; the simple fruits are drupes (=carpels) inserted on a receptacle, which also bears a persistent calyx. (5) Strawberry: the fruit is compound, and consists of many achenes (=carpels), and a large fleshy receptacle bear- ing a calyx with an epicalyx. (6) Rose: the fruit is compound, consisting of many achenes (=carpels) attached to and concealed in a hollow receptacle which bears a persistent calyx. CHAPTER XIII THE DISPERSAL OF SEEDS, AND A SUMMARY WITH REGARD TO THE FLOWERS IN one season a single plant, say a Foxglove, may produce thousands of seeds. If every one of these seeds is to be afforded an opportunity of developing into a mature plant, means must be pro- vided to enable the seeds to reach suitable spots at some distance from the mother-plant. The seeds of flowering plants are con- veyed through the air in the same manner as the pollen, in so far that they are either violently ejected (eg. Bal- sam, Oxalzs), or are carried by the wind (¢g. Dande- lion), or borne by animals (e.g. Rose, Cherry, Galium). Explosive fruits are not common. The capsule of the Violet opens into three boat-shaped valves, each containing a double row of smoothly - polished _ seeds. The sides of the boat-shaped valves contract as they dry, and fling out the seeds. To understand this mechanism, we have only to remember the manner in which an orange-pip springs out when squeezed between two fingers. nee Fig. 129.—Right-hand figure is a vertical section of infructescence of Dandelion: 6r= involucre. Left-hand figure is a vertical sec- tion of a single fruit (achene) with a pappus ZA) on a long beak; gc=pericarp ; ¢s=testa of the seed ; cof=cotyledons ; 7=radicle. Dispersal by the wind.—To facilitate dispersal by the 95 96 DISPERSAL OF SEEDS agency of the wind, the fruits or seeds are very small; or they oppose a large surface to the wind. The large surface may be merely due to the flattened form of the fruit or seed, or it may be caused by the possession of wings or tufts of hair. It is to be noted that when fruits (or their carpels in the case of schizocarps) are closed and indehiscent, they (or the meri-— carps) are the parts scattered, and adapted to aid dispersal; the seeds in this case are passively borne inside the fruits. But if the fruit dehisces, ° or is open (eg. Gymnosperms), the seeds are the parts scattered, and, as a rule, it is they and not the fruits which are adapted for transference to distant spots. The following table shows the corresponding mechanisms, or forms, in fruits and seeds to aid dispersal by the wind :— Fig. 130.—Samara im. Fruits DISPERSED (Fruits indehiscent or separating). SEEDS DISPERSED (Fruits dehiscent or open). Mechanism or ‘Form. Nutlets of Labiate. Mericarps of many Um- 1. Minute size. 2. Flattened form. Orchid (Fruit = capsule). Wallflower (Fruit = 3. Wings. 4. Tufts of hair. seligua). Scotch Pine (is a Gym- nosperm), fig. 67. Willow, Poplar, Willow- herbs (Fruits are cap- sules). belliferae (fig. 185). Samaree (fig. 130) of Elm, ‘Birch, and Sycamore. The achenes of many Compositee (Dandelion, etc.) with a jpappus (fig. 129). Achene of Clematis with a hairy style. Dispersal by clinging to Animals.—Many fruits possess hooks, or rough or sticky surfaces, which cause them to adhere to animals which happen to brush against them. It is usually the fruit, not the seed, which possesses hooks, etc. As examples may be cited, the “burrs” of the infructescences of many Composite (Daisy-family), the hooked achenes of Geum, and the fruits of Galium (Goose-grass). Seeds dispersed by being transported inside Animals.— It is to be noted that when the seeds or fruits are scattered by DISPERSAL OF SEEDS 97 the wind, or by clinging to animals, the fruits are dry, whereas seeds or fruits which are dispersed by being carried inside animals are usually possessed of conspicuous and fleshy coats, which invite animals to notice and eat them. The fruits being eaten, the seeds are protected by an indigestible stone (in drupes) or testa (in berries and Gymnospermous fruits), and pass through the body of the animal uninjured. When the fruit is indehiscent it is usually the pericarp which is succulent and invites the animals which effect the dispersal of the fruit. When, on the other hand, the carpels are. open, as in Gym- nosperms and dehiscent fruits, the seed is often brightly coloured, and may have a.succulent inviting outgrowth (the aril). SEEDS DISPERSED. Fruirs DISPERSED. (a) Fleshy aril— (a) Fleshy pericarp— Seeds of Yew (Gymnosperm) Drupes of Cherry, Blackberry, with bright-red fleshy Raspberry, distributed by birds. “aril,” distributed — by Larger drupes of plums, etc., birds. distributed by larger animals (Mammals). Berries of Mistle- toe, Currants, distributed by birds. (6) Fleshy or coloured receptacle— Rose-hip, Strawberry, both dis- ‘ tributed by the agency of birds. Protection of the embryo in the seed.—The embryo and food-substance inside the testa require protection against climatic influences which would hasten their disorganisation and decay, and against attacks on the part of animals and fungi. The embryo and food-substance are therefore protected by a firm hard coat. When the fruit is dehiscent and the seeds travel naked, the testa is thick and strong (e.g. Wallflower, Bean). When the fruit is dry, indehiscent or separating, the seed is protected by the pericarp, and there is no necessity for the testa to be so thick—in fact, it may be quite imperceptible or absent (e.g. Grasses). Finally, in fleshy indehiscent fruits the stony layer of the pericarp of drupes protects the embryo, and the testa is thin, whereas in berries there is no stony layer, so that the testa of the seed must be well developed G 98 FUNCTIONS OF REPRODUCTIVE PARTS in order to withstand the action of the digestive juice of animals which eat the fruits. SUMMARY OF THE FUNCTIONS OF PARTS OF FLOWERS, FRUITS, AND SEEDS. 1. The calyx usually protects the young flower bud (e.g. Poppy). It may also serve as a means of attracting insects by its colour (¢.g. Clematis), or act as a factory (e.g. Mallow), or as a receptacle for honey (e.g. Wallflower). Sometimes the calyx aids in the dispersal of the seeds by the agency of the wind (e.g. pappus of Composite). 2. The corolla serves to attract insects which will effect cross- pollination. It may further bear nectaries (e.g. Buttercup). 3. The andrecium.—The pollen pollinates the flower, and is indispensable for the production of seed. The anther manufactures the pollen. The filaments bring the anthers into the position which will lead to cross-pollination by wind or insects, or to self-pollination. As good ex- amples, illustrating the fact that the length of the filaments ‘is to be explained in accordance with the method of pollina- tion, we have but to compare and contrast the flowers of the Primrose, of Grasses, and the cleistogamic flowers of the Violet. The time and direction of dehiscence also are related to the method of pollination; we note, for instance, the introrse dehiscence of the Violet and of Composites, the extrorse dehis- cence in the Buttercup when the flower opens. 4. The gynecium.—The embryo-sac in each ovule is the region in which the embryo and its food (endosperm) arise. The ovary protects the ovules. The stigma receives the pollen- grains. The style raises the stigma to the proper height so as to bring about cross-pollination or self-pollination. The size, shape, and time of ripening of the stigma and style bear relation to the method of pollination (see Grasses, Composites, Violet). 5. Sugar.—Sugar is excreted in flowers in order to attract’ insects which will effect cross-pollination. Sugar is manufactured in many fruits, and is responsible for their sweetness of flavour, in order to allure animals (mainly birds in this country) which will disperse the seeds. 6. Pericarp.—The pericarp protects the seeds and often facilitates their dispersal. Often it is brightly coloured so as to attract the notice of animals. It may or may not dehisce. FUNCTIONS OF REPRODUCTIVE PARTS 99 7. The testa serves to protect the embryo and food-sub- stance of the seeds. Consequently it is thin and delicate when the seeds are adequately protected by the pericarp. 8. Wings, hooks, and hairs on seeds or fruits serve to facilitate the dispersal of the seeds. Sometimes the hooks or spines may also aid in protecting the fruits against animals which would eat them and destroy the seeds. PART 11 CLASSIFICATION OF ANGIOSPERMS CHAPTER XIV CLASSIFICATION ' WHEN a number of plants are so closely alike that they obviously may be the offspring of one original parent, they are said to be a number of zzdividuals. all belonging to one species. But if two or more plants are very similar, yet exhibit certain constant slight distinctions, they are described as being different species of one genus. For example, in English meadows there are to be found three common kinds of Buttercups—the Bulbous Buttercup, the Creeping Buttercup, and the Meadow Butter- cup. As they possess so many characteristics in com- mon, they are included in one genus, Ranunculus; but as they each display certain characteristics peculiar to them- selves, they receive distinct species-names, and are known as Ranunculus bulbosus, R. repens, and R. acris respectively. When the divergences between two or more plants are more considerable, they are referred to different genera. For ex- ample, the Clovers are included in the genus Z7ifolium. Comparing the various genera thus constituted, they exhibit amongst themselves both resemblances and dissimilarities. Those genera which are sufficiently alike are grouped together to form a family or order; so that all genera are included in certain orders. Thus the Buttercups (Ranunculus) and the Marsh Mallow (Caétha) are included in one order, the Ranun- culacee ; whilst the Clovers (Zzfolium) and Vetches (Vicia) belong to another order, the Leguminose. In like manner the families may be grouped together to form cohorts, then series, then sub-classes, and finally classes; but this statement will be more easily understood after glancing through the follow- ing scheme of classification of some of the Angiosperms :— ANGIOSPERMS. Crass J. : Dicotyledons.—Seedling has two cotyledons. Leaves net-veined. Floral leaves in fours and fives. 103 104 CLASSIFICATION OF DICOTYLEDONS Cuass II.: Monocotyledons.—Seedling has one cotyledon. Leaves parallel-veined. Floral leaves in threes. CLASS I.: DICOTYLEDONS Sup-Ciass I. : APETALA. Petals absent. 1. Cupulifere. Flowers epigynous diclinous. ¢ flowers in catkins. Fruit’ indehistent one-seeded. Trees or shrubs. 2. Salicacee.. Flowers hypogynous diclinous. 4d flowers in catkins. Fruit dehiscent with many seeds. Trees or shrubs. [3. Euphorbiacee.* Flowers diclinous. In the fruit the three (sometimes two) carpels separate and open ; one or two seeds in each chamber. | Sup-Crass II.: POLYPETAL. Corolla polypetalous. I. Thalamifiorse.—Flowers hypogynous without a well-developed disk. (a) Gynecium apocarpous. 4. Ranunculacee*. Stamens indefinite. (b) Ovary syncarpous with parietal placentation. 5. Papaveracee. Flowers actinomorphic. Sepals and petals in twos or threes. Stamens indefinite. 6. Fumariacee.. Flowers zygomorphic. Sepals and petals in twos. 7. Crucifere°’. Flowers actinomorphic. Sepals and petals four each. Stamens two short and four long. 8. Violacee. Flowers zygomorphic. K5 C5 A5 G (3). (c) Ovary syncarpous. Placentation free-central. 9. Caryophyllacee’. Flowers actinomorphic. Stamens ten or fewer. , * This is not the correct systematic position of the Euphorbiacez ; but the family is placed here because it is easier for beginners to identify plants belonging to it when it is classed amongst the Apetale. CLASSIFICATION OF DICOTYLEDONS 105 (d) Ovary syncarpous. Placentation axile. 10. Malvacee. Flowers actinomorphic. Stamens indefinite, filaments united and adhering at the base to the corolla. Anthers one-lobed. II. Discifiore. Flowers hypogynous with a distinct disk. 11. Geraniacee’, Flowers actinomorphic. Stamens 5 + 5 (obdiplostemonous) or five only. Fruit beaked with five chambers, each with one seed. 12. Oxalidacee. Flowers actinomorphic. Stamens 5 + 5 obdiplostemonous. Fruit five-chambered, with a number of seeds in each chamber. III. Calyciflore. Flowers perigynous or epigynous. (a) Perigynous usually. Gynectum apocarpous. 13. Papilionacee’. Flowers zygomorphic, papilionaceous, weakly perigynous. Stamens ten, with the filaments all combined, or one separate from the other nine. Carpel one. 14. Rosacee®. Flower actinomorphic. Stamens usually in- definite (rarely epigynous). (b) Epigynous. Gynecium syncarpous. 15. Umbellifere*. Flowers actinomorphic in umbellate in- florescences. K5 or0 C5 A5 G(2). Fruit a schizocarp. Sup-Criass JII.: GAMOPETAL. Corolla gamopetalous. (a) FLowErs Hypocynous. Gynecium syncarpous, (1) Flowers actinomorphic (stamens equal in number to the petals ; corolla regular.) 16. Primulacee*. Placentation free-central. Stamens equal in number to the petals opposite to them. 17. Convolyulacee. “Ovary two- (three-) chambered, with two ovules in each chamber ; sometimes each chamber sub- divided by a false partition into two halves, each con- taining one ovule. Twining herbs. 18. Solanacee. Ovary two-chambered, with several ovules in each chamber. 106 CLASSIFICATION OF MONOCOTYLEDONS 19. Boraginacee. Ovary four-lobed, four-chambered, with one ovule in each chamber. Fruit four nutlets. (2) Flowers zygomorphic (stamens fewer than the petals ; corolla irregular). 20. Labiate*. Ovary four-lobed, four-chambered, with one ovule in each chamber. 21. Scrophulariacee. Ovary two-chambered, with several ovules in each chamber. (b) Flowers Epicynous. Gynecium syncarpous. 22. Caprifoliacee. Ovary two- (three-) chambered. Leaves. opposite. 23. Composite’. Inflorescence a capitulum, Anthers united. Ovary one-chambered, with one ovule. CLAss II.: MONOCOTYLEDONS 1. PERIANTH PETALOID. Ovary syncarpous. (a) Flower actinomorphic (perianth regular, ovary inferior). 24. Liliacee’. Stamens six. (b) Flower actinomorphic. Ovary inferior. 25. Amarylidacee. Stamens six. 26. Jridacee. Stamens three. — (c) Flower zygomorphic. Ovary inferior. 24. Orchidacee. Perianth irregular. Usually only one anther present ; it is gynandrous. i. PERIANTH small or absent. (a) Flowers ? 3 ona spadix usually in a spathe. 28. Aracee. (b) Flowers usually % in spikelets invested by chaffy bract-scales. 29. Gramineae. . [It will be well for young beginners to confine their attention to those families which are specially marked with the sign ° in the above list.] APETALA—CUPULIFERZ 107 DICOTYLEDONS. CUPULIFERZ (Oak Family). Trees or shrubs. Leaves simple. Moncecious. Staminate inflorescence usually a catkin. Flowers small, inconspicuous, apetalous. Perianth small, green, or absent. Carpels two or three (rarely four or six), syncarpous, inferior, usually with a two or three-chambered ovary ; one or two ovules in each chamber. Fruit one-seeded, indehiscent, often a nut. Seeds without endosperm. Type: HAZEL (Corvlus avellana). Vegetative Characters.—Shrub: the main stem breaks up into several larger branches a short distance above the ground. The main root present in the seedling grows only for a short time ; it gives off several lateral roots which run hori- zontally close beneath the surface of the soil. These horizontal roots (or the base of the stem) frequently produce slender adventitious shoots—suckers—which grow vertically upwards. These shoots, in turn, can produce adventitious roots of their own at their bases, and subsequently may become disconnected from the mother-plant by reason of the decay of the connect- ing parts. Thus the Hazel may multiply by suckers (compare Raspberry canes and Rose trees). Leaves alternate, arranged in two rows, or on vigorous suckers often in three rows, with small stipules which soon fall ; the margin is twice-serrate. It will be noted that in the bud- condition the two halves of each leaf are folded together along the mid-rib: the one half of the leaf is slightly larger than the other and overlaps the latter in the bud. On the approach of winter the stem ceases to elongate, and produces a terminal resting-bud. This resting-bud is clothed externally by leaves whose stipules are developed into scales, but which possess no lamina. Inasmuch as the leaves are ranked into two rows, their stipules naturally are arranged into two double rows. Consequently these bud-scales are arranged in pairs on opposite sides of the stem, and each pair of scales represents the two stipules of one leaf. The lateral (vegetative) 108 DICOTYLEDONS resting-buds are similar, but they have in addition two scale- like prophylls inserted below the remainder of the scales. Within the scales are hidden the young foliage-leaves. In February or March the plant blossoms before its vegetative buds unfold; when the latter become active their scales drop off after being forced apart by the growing stem and by the emerging foliage-leaves (figs. 6-11). Inasmuch as these scales were set close together, after they have fallen their scars form small groups; whereas the fallen foliage-leaves, having been separated by longer internodes, are represented by scars which are widely separated along the stem. Consequently, on parts of the stem which are from one to three years old, it is easy to recognise which portions bore scales. Each such group of scale-scars represents one winter. We can, there- fore, tell the age of a tolerably young stem by counting the number of its groups of scale-scars. Thus, if we com- mence at the apex of a resting vegetative shoot, the por- tion of the stem which connects it with the first group of scale-scars represents one year’s growth. Again, travelling farther down, that part of the stem which connects this first group of scars with the next lower group represents another (previous) year’s growth, and hence it is two years old, and sO on. Inflorescences.—The stamens and carpels do not occur together in the same flowers. The staminate flowers are arranged in pendulous spikelike inflorescences — catkins. The carpellary flowers are grouped together in small bud-like inflorescences, which can be recognised by the tufts of red stigmas which protrude from their tips. Both kinds’ of inflor- escences are borne upon certain axillary dwarf-branches. In order to understand the arrangement of these dwarf-branches, we will follow the growth of a vegetative bud which com- mences to sprout in spring. The bud opens, the stem emerges and grows during the summer, and bears foliage- leaves. In the axils of these leaves three varieties of buds arise—vegetative buds, buds enclosing the young carpellary flowers, and buds destined to grow out into branches bearing the staminate inflorescences. The first two forms of buds are externally similar; they are resting-buds, and remain dormant during the following winter. But the third type of bud grows out at once and develops into a dwarf-branch. This APETALZ—CUPULIFERA 109 branch has no foliage-leaves, but it bears on its basal parts a number. of scales, whilst its terminal portion is a staminate inflorescence (catkin). In ad- dition, lateral catkins may arise in the axils of one or two of the higher scales of this dwarf- branch. The scales soon drop off. Thus, when we examine the Hazel-trees flowering in February (see fig. 131), we find the staminate catkins (¢) are arranged, usually several to- gether, on short branches of the previous year’s stem: the catkins rest naked through the winter. The buds (?) enclos- ing the carpellary flowers now show that they are not vegeta- tive resting-buds, a tuft of red stigmas protrudes from their tips. These buds also stand laterally on a part of the stem which was formed in the pre- vious year; also occasionally in the axils of the basal scales of the dwarf- branch which bears the catkins. Staminate Inflorescence (fig. 131 ¢).— The inflores- cence consists essentially of a number of bracts and axillary flowers, which are spirally ar- ranged on a long axis. There is one flower in connection with each bract. Two prophylls (fig. 132, p7), representing the 4.706 3t- The stom fom thesenle soars first two leaves on the flower- (sc) was produced in the previous'year. The stalk, are present, but are sorioulnaNes have fallen off; v=vegetative fused with the bract (47), for ; no flower-stalk occurs. The staminate flower (fig. 132) con- IIo DICOTYLEDONS sists solely of four stamens, which are attached to the bract in place of being on a flower-stalk in the axil of that bract. 132 133 a” Fig. 132.—Staminate flower of Hazel inserted on bract (47), with which two prophylls (47) are fused. Fig. 133.—Diagram of ditto. oe Each stamen is halved almost to the base of its filament, so that at first sight there appear to be eight stamens, each of which possesses only half a complete anther. The anther is crowned by a tuft of hairs, The bud of the dwarf branch (fig. 134) which produces the carpellary in- florescence is often , loosely described as being the in- florescence. The bud is really the commencement of a foliaged branch which terminates in an inflorescence; but the foliage-leaves do not unfold till after the flowering is over. On the axis of this bud the most external and lowest leaves are two prophylls ; then succeed three to four pairs of scale-like stipules (sc), and’. within these two to four foliage-leaves.' Thus so far the bud is like a vegetative bud; but above these foliage-leaves follows the true inflorescence. The carpellary inflorescence consists of four to eight spirally-placed bracts (ér) with axillary flowers, which are borne on a shortened axis. In the axil of each bract (fig. 135) there stand the buds of two carpellary flowers, so that the whole inflores- cence possesses eight to’ sixteen flower-buds. But only a few of the flower-buds develop into mature flowers. Each carpellary flower has a minute, indistinctly lobed, green perianth (Ze), which is inserted on the Fig. 134.—Vertical section of bud of Hazel terminating in a carpellary inflorescence, APETALE—CUPULIFERA uae ovary. The flower is therefore epigynous. The inferior ovary is two-chambered, and is surmounted by two long purplish-red thread-like stigmas (sg) ; thus the gynecium consists of two ty r It eo a ae Fig. 135.—Two carpellary Fig. 136.—Diagram of ditto. flowers of Hazel in the axil of a bract (67). carpels, and is syncarpous. The ovules do not develop until after the pollination of the stigma (fig. 137) ; consequently it is useless to look for ovules before pollination. Each chamber of the ovary (ov) then contains one ovule (0). At the base of each flower (z.e. below the insertion of the ovary) there is a little cup-like envelope (477)-—an involucre. It is well to note that this is not a calyx or a perianth ; it isa collection of bracts.* ; Fruit. — After pollination the ovules are produced, but, as a rule, only one ovule in an ovary develops fully so as to form a seed. The fruit (fig. 138) is a OR ihr Sat nut containing the one seed. The ~ Fig. 138.—Vertical section of nut of involucre originally investing the #7 base of the ovary grows vigorously and forms the green cup (fig. 139, ) round the fruit. Seed.—The kernel of the nut is the seed; it has a thin papery testa (¢s), but possesses no endosperm. The main mass of the seed is * It is impossible to explain in this book the exact method in which this involucre is formed ; but in reality it represents three joined bracts which are also prophylls. The diagram 136 explains the nature of the cupule and the inflorescence in the axil of each bract. 112 DICOTYLEDONS constituted of the two large fleshy cotyledons (cof) of the embryo. Dissemination.—The fruits merely fall to the ground, or may be carried away by animals (especially squirrels) for future use. Pollination. The flowers are wind-pollinated. When the Fig. 139.—Two nuts of Hazel invested with cupules (cd), staminate catkins have ma- tured they bend down, and, as their bracts separate, the anthers dehisce and drop pollen on to the bracts below them. The pendulous cat- kins are easily shaken by the wind, and the pollen may reach the tufts of stigmas. (i.) Note the inconspicuousness of the flowers which are not visited to any appreciable extent by insects. (ii.) That a large amount of dry pollen is produced, and easily shaken from the flowers. (iil.) The large filamentous stigmas. . (iv.) The absence of nectaries. All these are common features of wind-pollinated flowers. APETALA!—CUPULIFERZ 113 TABLE ILLUSTRATING THE FLORAL CHARACTERS OF OTHER CUPULIFERZ. BirCH (Betula). Oak (Quercus). BEECH (fagus). & INFLORES- CENCE. Catkin: 3 flowers in the axil of each bract. Note two pro- phylls lying within the bract. Catkin, pendu- lous: 1 flower in the axil of each bract. No prophylis. Head-like cluster pendulous. d FLower. Perianth 2—1I- phyllous. Sta- mens 2, halved, therefore ap- parently 4 4- anthers. Perianth 6-7- lobed. Stamens 6-12. Perianth 4-7-seg- mented. Sta- mens 4-12. 1 Q INFLORES- Catkin : 3 flowers in the axil of each bract. Note that the Erect head-like spike: 1 flower in the axil of each bract. Head-like cluster, 2 flowered, erect. CENCE. bract is fused| Usuallyno pro- with two pro-| phylls visible, ' phylls. but a basin-like cupule occurs. Perianth absent. | Perianth 3 + 3. | Perianth 3 + 3. Ovary 2-cham- Ovary 3-cham- Sa scheme bered, each bered, each bered, eac aE nes chamber I-ovu- chamber 2- chamber I- late : styles 2. ovulate: style| ovulate: styles I, stigma 1. 3. 1-seeded winged | Acorn =a nut|The 4- valved achene(samara) with a woody cupule encloses No cupule. cupule. Note the infructes- that of the six| cence of two Fruit. ovules in an] fruits. Fruit ovary, only one (from one develops intoa| ovary) is a seed. 3-angled, 1- seeded nut. For the remaining characters of these three trees, see the characters of the family. H 114 DICOTYLEDONS SALICACEZE (Willow Family) Trees or shrubs. Leaves alternate stipulate. Dicecious. The inflorescences are catkins. The staminate flower consists of two or more stamens and a disk. The carpellary flower consists of a hypogynous disk, and a syncarpous superior gynecium composed of two carpels: ovary, two-chambered, with many ovules on two parietal placentz: stigmas, two. Type I.: COMMON SALLOW or WILLOW (Sadix caprea). Vegetative characters.—A tree or shrub, with alternate, stipulate leaves. Each resting-bud is completely encased in 145 Figs. 140-145.—Inflorescence and flowers of Salix caprea (Willow). Fig. 140.—Vertical section of staminate inflorescence. Fig. 141.—Staminate flower inserted on a bract. Fig. 142.—Diagram of ditto. Fig. 143.—Carpellary inflorescence. Fig. 144.—A carpellary flower inserted on a bract. Fig. 145. iagram of ditto. two bud-scales. Many of the terminal buds of the branches die in late autumn and drop off during the winter, and in the APETALZ—SALICACEA II5 following year the highest axillary bud of these branches shoots out, and thus continues the growth of the branch. Thus the Willow-branches are sympodia. Inflorescences: the stamens and carpels do not occur on the same individual, the plant is dicecious. The flowers are arranged in catkins which are erect, not pendulous. Each catkin arises, in July, in the axil of a foliage leaf, on a part of the stem formed during that year. The foliage-leaves fall off in autumn. Consequently, when the catkins burst out in the following year (from March to May), they are seen to be in the axils of fallen leaves on a part of the stem which was produced during the previous year. The inflor- escences (figs. 140, 143) open before the foliage-leaves emerge from their buds. The axis of the inflorescence bears at its base a few scales, and higher up a number of scale-like bracts and axillary flowers. One flower stands in the axil of each bract. The staminate (6) flower (fig. 141) consists of two stamens (a) and a greenish nectary (z) situated on the base of a bract (4). The stamens have long filaments, extrorse anthers, and sticky pollen. The carpellary (¢ ) flower (fig. 144) is also inserted on a bract (4); it consists of a nectary () and a syncarpous gyneecium composed of two carpels. The ovary (ov) is stalked, and has one chamber which contains many ovules attached to two parietal placentee. ‘he single short style forks above into a two-armed stigma (sg). The nectary is regarded as part of the flower, and, being inserted below the ovary, the flower is described as hypogynous. Fruit and dissemination.—The fruit is a two-valved capsule which allows the escape of the numerous minute seeds. The seeds are scattered by the wind, and each seed is possessed of a tuft of silky hairs, which forms the sailing mechanism. Type II.: POPLARS (Populus). Poplar-trees differ from the Willows in having pendulous catkins, staminate flowers with from four to an indefinite number of stamens [some Willow flowers have as many as five stamens], and dry pollen. Moreover, the flowers have no nectaries, though they possess a hypogynous basin-like out- growth, which is regarded as either a disk or as a perianth. Pollination of the Willow and Poplar.—The Willow is insect- pollinated, whereas the Poplar is wind-pollinated. In accord 116 DICOTYLEDONS ance with these facts we note that the catkins of the Willow are erect, its flowers produce honey, and its pollen is sticky. But the catkins of the Poplar hang loosely and are easily shaken by the wind; the flowers produce no honey; the pollen is dry ; and finally the stigma, being lobed to a greater extent than in the Willow, it offers a larger surface for the reception of the pollen. EUPHORBIACE (Spurge Family) Plants sometimes having a milky juice. Flowers usually apetalous, diclinous, hypogynous. Perianth small or absent. Gynecium, syncarpous, with a lobed three- (rarely two-) chambered ovary, having one-two ovules in each chamber. Fruit a capsule. Seeds endospermic. Type: PETTY SPURGE (£uphorbia peplus). Vegetative characters.—An annual herb containing a white milky juice and with simple leaves. Inflorescence: the stem, which is simple or has two large branches, terminates in a compound inflorescence, which is an umbel-like cyme of three Fig. 146.—Cyathium of Euphorbia peplus. branches. Each of the latter is in turn a two-branched cyme (dichasium), the branches of which may again be forked cymes (dichasia). But throughout the whole inflorescence the actual termination of each shoot is formed by a peculiar inflorescence termed a Cyathium, which looks like a simple flower (figs. 146, 147).—The cyathium has a cup-like in- EUPHORBIACE 117 volucre (27) formed by the union of five bracts (47) which collectively surround a number of flowers. At the points of junction of four of these bracts are four crescent-shaped nectaries (#), often described as g/ands. Within the involucre a Fig. 147.—Vertical section of cyathium of Euphorbia peplus. number of stamens (a, az, an’) and small scales (sc) appear to be ranged round a long-stalked three-lobed ovary (ov). Staminate flower (fig. 148) : each apparent stamen is really a naked stamin- ate flower consisting of only one stamen situated on a flower- stalk. A jointin the stalk of the stamen represents the point at which the filament is inserted on the flower- stalk. The part below the joint is the flower-stalk (st), and the portion above is the stamen with a filament (f). [In a plant which is closely related to Euphorbia there is a little perianth at the joint. ] The floral formula is KO CO Al GO. These stamen-like flowers are arranged in five lines opposite the five bracts* (figs. 149, 150). Each of these radial lines of staminate flowers represents an inflorescence standing in the axil of a bract _ (diagram 149). Carpellary flower (figs. 146,147): startatt tower the single central gynzecium with its long stalk of Euphorbia 2 peplus, and an represents a simple naked flower composed of “adjoining scale three carpels. In some.spurges there is a distinct “?: hypogynous perianth, consisting of three or six perianth-leaves : even in the Petty Spurge there is a trace of this perianth (Ze). The ovary (ov) is three-lobed and three-chambered, with one * This is more clearly seen in a large cyathium like that of Zaphorbza lathyris. 3 118 DICOTYLEDONS ovule (0) in each chamber. There are three forked styles with stigmas (sg) on the summit of the ovary. The floral formula is KO (minute) CO AO G (3). Fruit.—The three-lobed ovary forms a three-valved capsule. Seed.—Endospermic. We see therefore that the cyathium (figs. 149, 150) is a cymose inflorescence consisting of one terminal carpellary- Fig. 149.—Diagram of cyathium Fig. 150.—Scheme of cyathium of Euphorbia. 1, 2, 3, 4, 5 are of Kuphorbia. 1, 2, 3, 4, 5 are bracts. bracts. flower and lateral staminate inflorescences arising in the axils of five bracts which form the involucre. RANUNCULACEZ (Buttercup Family) Usually herbs. Leaves alternate (except Clematis). Flowers, usually showy, acyclic or hemicyclic, regular (except Monks- hood and Larkspur), hypogynous. Sepals polysepalous, often petaloid. Petals polypetalous or absent. Stamens numerous. Carpels usually more than one, apocarpous, superior. Seed endospermic. . Type I.: BUTTERCUPS (Ranunculus acris, R. bulbosus, R. repens). Vegetative characters.—Perennial herbs. Leaves alternate, simple, deeply divided. Stipules are absent, but there is a leaf-sheath at the foot of the petiole. In the first two species POLYPETALASX—RANUNCULACE 119 the stem is erect, and in /. dudbosus it is swollen at the base. In &. vefens the stem is not erect, but forms creeping runners, which are fixed to the soil by adventitious roots given off from the nodes. Inflorescence:—cymose; the axis ends in a flower. When present, the lateral inflorescences are two- branched (dichasia) or one-branched (monochasia). Note the two small prophylls.on each lateral axis of the inflorescence, and that in the region of the flowers the leaves are simplified; they are bracts. Flower (figs. 60, 61).—The flowers of these three species of buttercup are so alike that one general description will suffice. The flowers are hemicyclic, monoclinous (%), regular, and hypogynous. Sepals (cal, sp) five, separate, green. Petals (cor, p) five, alternating with the sepals, separate. Note that there is a little pocket—the ectary ()—at the base of the inner face of each petal. Stamens (and) numerous (0c), hypogynous, spirally arranged, separate. Carpels (gyn) numerous (00), apocarpous, superior, spirally arranged on a conical receptacle (r). Each carpel contains one basal ovule (#) in its one-chambered ovary; style, very short ; stigma, knob-like. Fruit :—compound, consisting of numerous achenes (fig. 115) upon a common receptacle. (Each achene is derived from one carpel.) Seed endospermic (evd) with a minute embryo (em). Pollination.—The outermost stamens ripen before the inner ones and before the carpels. Their anthers dehisce towards the petals. At this early stage the flower is practically staminate, for the stigmas cannot be pollinated because they are not ripe, but are covered by the closed anthers of the inner stamens. Gradually the rest of the stamens ripen and dehisce, but the stigmas are ready for pollination before the innermost stamens have dehisced. Thus, when it first opens, the flower cannot be pollinated, subsequently it can be either cross-pollinated or self-pollinated. Many kinds of insects (beetles, flies, bees, and butterflies) visit the flowers for the sake of the scarcely-concealed honey or for the pollen, and act as pollinating agents. Type II.: MONKSHOOD (Aconitum napellus). The Monkshood differs from the Buttercups in_ the following points :—Jnflorescence, a terminal raceme. Calyx (ps, as, ds) blue, petaloid; of the five sepals the posterior 120 DICOTYLEDONS one (fs) is hood-like; irregular. e¢a/s eight; the two posterior (ff) petals are long-clawed nectaries concealed under the large posterior sepal; the other petals (af) are small or absent. There are three separate carpe/s, each with many parietal ovules in the ovary. The fruit consists of three follicles. The flower is irregular, and is zygomorphic in a median plane. Pollination.—The flower is proterandrous ; 151 152 Figs. 151, 152.—Flower of Monkshood : dr=bract ; 4r=prophylls. pollination by its own pollen appears to be thus rendered impossible. Cross-pollination is accomplished exclusively by the aid of humble-bees. As the humble-bee alights on the flower, it uses the two lateral sepals as a platform, and the consequence is that the lower surface of the bee’s body comes into contact with the anthers and stigmas. In freshly-opened flowers it is the anthers against which the insect strikes. But in older flowers the stamens have bent back, and the stigmas, which are now ripe, touch the lower surface of the body of the bee at precisely the same spot as do the anthers in a younger POLYPETALA—RANUNCULACE 121 flower. This arrangement favours cross-pollination. The insect, when visiting the inflorescence, commences at the lowest flowers, and travels up the inflorescence. In this manner pollination by the pollen even of the same plant is averted. The long-stalked nectaries are completely concealed from out- side view, nor can their honey be reached excepting with great difficulty by any insects other than humble-bees. The Monks- hood-flower is a flower especially adapted for pollination by the agency of these particular insects, consequently it is absent from those regions of the earth which are without humble-bees. Comparison between the pollination and flowers of the Butter- cup and of the Monkshood.— The yellow Buttercup - flower is actinomorphic, and is directed upwards. Inasmuch as its nectaries are feebly concealed and easily accessible, insects with quite short tongues can discover and reach the honey. The flower is therefore visited by many (more than sixty) kinds of insects. These alight on the petals or on the carpels, and may cause cross-pollination or self-pollination. The blue Monks- hood - flower is zygomorphic, and is inclined to the horizon. Its honey is carefully concealed and protected, so that only specialised insects can discover and reach it. The flower is pollinated exclusively by one group of insects—humble-bees— which visit in one particular way, and necessarily effect cross- pollination as they go from plant to plant. Self-pollination is impossible in the Monkshood-flower. The Monkshood- and Buttercup-flowers thus illustrate the fact that the colours and shapes of flowers are associated with the varieties of insects which visit and pollinate those flowers. We also see that the irregular zygomorphy is a means employed to cause the visiting insect to deal with the flower in a particular manner so as to ensure cross-pollination. Finally, we note that the zygomorphic flowers are associated with certain classes of insects, not, as is the Buttercup, with many varieties of flower-visiting insects. [TABLE DICOTYLEDONS 122 “spejod peurol om} juas -aidar Aeut ATqts -sod yorym ‘nds ~paiinds st 10119} -sod = £ xepndor11 ‘(se2vlp wneuryg 2 *a[OTToF ‘1 | anfq xo0waysod ‘x |‘ proreyed ‘antq ‘S s eq) = andsyeT : “(sap : “ay = Szyquvaz) ‘azonjoauy | ‘sapTT[O.y |*satzejoou repnqny ‘g *proreyed ‘9 @ ayuooy =: ayUT AA. ‘spedas -so1e]99u *plo[ pue sjoviq 0} saaval re]nqn} ‘pesueze -eyjad = sauitjautos *(52.40991]277 ) -aBerjoy wo uctsuery, | ‘soporjog | Aqyerds “€1 ynoqy | Guaysisrad = ‘adreT @ asoyy = SBUSTA) *sjadieo ay} Jo saseq *(seegsnqog vy7j0.) ) ayy fq payasioxe Aouopy | “sapot[oy ‘yuasqy | ‘propejed ‘morpa”, Ba posueyy =: ysaeyy ‘aronjoauy | ‘suey ‘yuasqy “plopeieg ‘ @ “quowsup sapAys Arayyeay JuaysIs -1ed_ @ Sutssassod pue ‘purm ayy Aq uMosq aUsyDY ‘Saavay ays -oddo oy} jo syyeis 94} jo suvaur Aq surqunyy | ‘saueppy ‘yuesqy “ploreieg @ “s2q01uaD “SALON as waa “STVLAg “sTvVdaS “AULANWAS “AWV NT ‘WAOVINONONVA UFHLO AO SUALOVUAVHO AHL ONIMOHS ATAVL POLYPETALAZ—PAPAVERACEAS 123 PAPAVERACEZ (Poppy Family) Herbs with milky juice. Leaves exstipulate. Flowers usually showy, regular, hypogynous. Sepals, two (three), polysepalous. Petals, 2+ 2, polypetalous. Stamens numerous. Carpels, from 2 to oo, syncarpous: ovary one-chambered, with many ovules on parietal placente. Fruit dehiscent. Seeds endospermic. Type I: FIELD-POPPY (fapaver rheas).* Vegetative characters.— Annual herbaceous plant, with milky juice (latex) and bristly hairs. Leaves alternate, stalked, Wy My joy ee iy My 1 H Y : lps ly % { I My Nt ; iy eB i “ Fig. 153.—Vertical section of flower of Poppy. without stipules, simple, pinnately cleft. Flower (fig. 153) solitary, terminal, actinomorphic, hypogynous. Sepals (sep) two, separate, falling off as the flower opens. etals (pf), 2+ 2, separate, arranged in two alternating whorls of two each ; the outer two also alternate with the two sepals. The petals are crumpled in the bud ; each petal may have a black spot at the base of its inner face. Stamens numerous (0), hypogynous. Carpels from eight to twelve, syncarpous, superior. Ovary (ov) one-chambered, with from eight to twelve parietal placente (f/) protruding inwards from the wall, and having many ovules on their faces (also fig. 155). Stigmas (fig. 154 5) from eight to twelve, sessile, forming velvety bands radiating * The flowers of almost any sort of Poppy may be examined in place of the one here described. 124 DICOTYLEDONS from the centre of the roof of the ovary. We should expect the stigmas to lie above the gaps between the placenta, because a stigma usually stands above the dorsal suture (mid-rib) of the carpel to which it belongs. But in the Fig. 154.—Gynzcium and Fig. 155.—Cross-section of one stamen of Poppy. ovary of Poppy. Poppy the stigmas ‘stand directly above the placenta, instead of alternating with them. When stigmas are thus superposed on the placentz they are said to be commissural. Fruit (fig. 126) a capsule, opening by lateral pores which alternate with the stigmas. Seeds minute, and easily transported by the wind. Pollination: the flower has no nectaries, but is visited by insects desiring its pollen. Type II.: COMMON CELANDINE (Chelidonium majus). Herb with yellow juice and yellow flowers. Its flowers differ from those of the Poppy in that the gynzecium consists of two combined carpels, with two commissural stigmas surmounting a one-chambered ovary possessed of two parietal placente. The fruit (fig. 121) is a segua, which has no septum; conse- quently the persistent placenta (7) (rep/um) forms an empty frame which bears the ovules. Uses, Peculiarities, etc. of Papaveraceze.— The latex of Papaver somniferum is the source of opium. Lschscholtsia is a familiar garden plant, with flowers tending to become perigynous. CRUCIFERZA (Wallflower Family) Herbs. Leaves alternate, exstipulate. Inflorescence, race- mose, usually without bracts. Flower, regular, hypogynous. POLYPETALA—CRUCIFERA 125 Sepals, 2+ 2, polysepalous. Petals, 4, polypetalous. Stamens, 2+4, two short and four long. Carpels, 2, syncarpous: ovary, divided by a false septum connecting two parietal placentee ; ovules numerous. Fruit usually a siliqua. Seed, no endosperm. Type I.: WALLFLOWER (Chetranthus cheirt).* Vegetative characters.—A perennial herb, slightly woody at the base. Leaves alternate, exstipulate, simple. Inflores- cence: a raceme without bracts. Note the absence of prophylls from the flower-stalks. Flower (fig. 156) actino- 156 157 Fig. 156.—Vertical section of flower of Wallflower. Fig. 157.—Floral diagram of ditto. morphic, hypogynous, brown or yellow, sweet-scented. Sepads 2+2, separate. The four sepals are arranged in two alternating whorls of two each. The two lateral sepals (c) form the inner whorl, and are inserted higher on the receptacle than the two outer median sepals. The lateral sepals are slightly enlarged * Almost any Crucifer will serve in place of the Wallflower, so uniform is the structure of the flowers, excepting as regards the nectaries. \ 126 DICOTYLEDONS and pouched at their bases: the little pouches act as recep- tacles to hold the honey poured out by the nectaries. Peta/s (p) four, separate, arranged in one whorl alternating with the four sepals. Note the blade (4a) and claw (c/) of each petal (fig. 83). Stamens (figs. 156, 88) 2+4, hypogynous, separate. There are two short stamens (a/) and four long ones (am). The two shorter stamens are opposite the inner (lateral) sepals, and are inserted at a lower level than the four long stamens. Therefore the two shorter stamens form an outer whorl, and the four long ones constitute an inner whorl of stamens. Vectaries (figs. 156, 88): a green nectary (7) is situated at the base of each of the two shorter stamens. Curfels (figs. 156, 88) two syncarpous, superior. Ovary (ov): the two parietal placenta, bearing numerous ovules, are connected by a delicate parti- tion (septum) which divides the cavity of the ovary into two chambers. When an ovary is divided into several chambers, and contains numerous ovules, the placentation is usually axile; but in the Cruciferze the ovules are attached to the walls, and not to the axial partition. It is for this reason that the partition is. regarded as not originally a true part of the carpels, and is therefore termed a false septum (fig. 156). The short style is surmounted by two commissural stigma- lobes (s). Fruit (fig. 120) a pod-like siliqua. It is necessary to distinguish between the persistent placente forming the replum (ve) and the false septum (fs). Seed (fig. 116) contains no endosperm, the embryo is bent. The seeds are compressed, and are easily carried about by the wind, and are thus able to reach the tops of walls, on which the plants frequently grow. TypEe II.: SHEPHERD’S PURSE (Cafsella bursa pastoris). This plant is an annual little weed, in reality an ephemeral, flowering at nearly all seasons of the year. The inflorescence and flowers are constructed on the same plan as those of the Wallflower. The length of the four long stamens is such as to occasion regular self-pollination. The fruit is of peculiar shape, and is a shortened siliqua. Uses, peculiarities, etc., of Cruciferee—Though they appear so different, Cabbages, Cauliflowers and Broccolis, Brussels- sprouts, Turnips, Rape, and Mustard are plants all belonging to the same genus—Svrassica, They are placed in one single POLYPETALA—VIOLACE 127 genus, because the flowers, fruits, and seeds are closely alike. The Cabbage (Brassica oleracea) is cultivated for the sake of its large leaves. The Brussels-sprouts is merely a variety of cabbage producing many large green axillary buds which form the edible portions. The Cauliflower and Broccoli are other varieties of the cabbage, cultivated for the sake of their much- branched inflorescences, the stems of which are fleshy and colourless, the flowers being reduced to minute buds. The “heart” of a Cauliflower or Broccoli is a branched terminal inflorescence. The Turnip (Brassica campestris) is a biennial possessing a tuberous main root, which we eat as a vegetable. The Swede is a variety of the Turnip, also cultivated for the sake of its swollen tap-root. The Rape is still another variety of B. campestris, and from its seeds colza-oil is obtained. The seeds of the Black Mustard (Brassica nigra) are the source of the condiment mustard. We use the young plants of the White Mustard (Brassica alba) in the composition of salads ; this is the Mustard cultivated with Cress to form “mustard and cress.” Cress (Lepidium sativum) is also one of the Cruciferz. The edible part of the-Horse-Radish (Cochlearia armoracia) is the rhizome (not the root): the leaves of the Horse-radish are stipulate. The swollen red. tubers of the Radish (Raphanus sativus) are formed mainly by the hypocotyl. Water-cress (Nasturtium officinale) also belongs to this family. A few Cruciferee are cultivated in gardens for the sake of their flowers: such are the Stocks, Candytuft (with zygomorphic flowers). VIOLACEZ (Violet Family) Herbs. Leaves alternate, stipulate. Flowers often showy, irregular, hypogynous. Sepals five, polysepalous. Petals five, polypetalous. Stamens five. Carpels three, syncarpous ; ovary one-chambered, with three parietal placente bearing many ovules. Fruit, a three-valved capsule. Type: PANSY (Viola tricolor). Vegetative characters.—Herb. Stem branched, with or with- out a rhizome. Leaves alternate, stalked; stipules large, leaf-like. Leaves rolled towards their upper faces in the bud. Inflorescence.—The flower is solitary, axillary. Note the two prophylls (fig. 158-3, 47) inserted at a considerable distance up 128 DICOTYLEDONS the flower-stalk. Flower median-zygomorphic, hypogynous. Sepals five, separate. Note the prolongation of the sepals below their points of attachment. /e¢a/s five, separate, irregular. The anterior petal is produced into a long spur Fig. 158.—Pansy. 1. Vertical section of flower : s=sepal ; /4=lateral petal ; ss=spur of anterior petal; a/=appendage of one of two anterior stamens. 2. Floral diagram. 3. Flower-bud, showing estivation: s=descending process of sepal. 4. Fruit: s/= placenta. 5. Flower with calyx and corolla removed : af=appendages of two anterior stamens; /=filament ; @=anther ; c=continuation of connective; s=swollen end of style ; v=shutter of stigma-cup. 6. Gynacium: ev=ovary. 7. Seed with lump (¢). 8. Vertical section of seed: ca=lump: s=micropyle; ¢=testa; e=endosperm. (1-6 based on Kny’s figures of Pansy.) (fig. 158-1, sf) which conceals the two nectaries and acts as a honey receptacle. The petals are arranged in the bud con- dition in the manner known as descending-imbricate. Stamens (fig. 158-5) five, hypogynous. Anthers (a) introrse, arranged close together round the single gynecium. The connectives are continued above the anthers, and form little flaps (c). The POLYPETALA!—_VIOLACE 129 filaments (/) are very short. The filament of each of the two anterior stamens sends a slender elongated process or appendage (ap) into the spur of the anterior petal, The green spots at the ends of these two appendages secrete honey, and are the nectaries. Carpels (fig. 158-6) three, superior, combined. Ovary (ov) one-chambered, with three parietal placentee which bear many ovules. Style (s¢) one, club-like, with a stigma in a pit (ch) on the anterior surface of its summit (s). Fruit (fig. 158-4) a capsule splitting down the dorsal sutures. The three valves contract and jerk out the smooth seeds. Seed (figs. 158-7-8) endospermic, with a lump (¢ ca) near the micropyle. Pollina- tion.—The anthers dehisce towards the gyneecium at the same time as the stigma ripens. At first sight it appears that self- pollination is inevitable ; and, indeed, self-pollination does take place in the whitish-yellow small-flowered variety of the Pansy (V. tricolor var. arvensis). But in the large-flowered variety of Pansy, which possesses variegated flowers, self-pollination is hindered by a very neat mechanism. The stigma-cup has a little shutter or flap (fig. 158-5, v) hinged on to its lower edge. A bee visiting the flower alights on the anterior petal, and, in order to sip the honey, it must push its tongue into the spur of the petal. In so doing, the tongue necessarily passes along the hairy groove between the stigma and the anterior petal. The pollen collects in this groove. Consequently, when the bee alights, its tongue first rubs against the stigma and drags open the “shutter,” so that any pollen previously present on the bee’s tongue is rubbed into the stigma-cup. As the tongue is pushed farther towards the honey it comes now for the first time into contact with the pollen belonging to the flower itself ; and in this way the tongue becomes coated with the flower’s own pollen. When the bee has obtained some honey and pro- ceeds to withdraw its tongue, the backward movement of the latter closes the shutter of the stigma-cup, and thus prevents the pollen of that flower from being rubbed into the stigma-cup. In the large blue or variegated flowers of the large-flowered variety of Pansy, the honey is so deeply placed (because the spur is long) that it can be reached only by insects with long tongues: these flowers are pollinated chiefly by bees and humble-bees. On the other hand, in the small yellow or yellowish-white flowers of the other variety of Pansy the honey is more easily accessible : consequently these flowers are visited I 130 DICOTYLEDONS by insects with shorter tongues (beetles and flies) as well as by bees. It is well to note that the yellow-flowered form has more accessible honey and a wider circle of visitors than the blue- flowered form, which is a “‘ bee-flower”; and to compare this with the case of the yellow Buttercup and the blue Monkshood. Some of the flowers of the small-flowered variety do not open, but pollinate themselves. The Violets belong to the same genus (Vzo/a) as the Pansy, and have their flowers constructed on the same general plan ; but the structure of the stigma varies in different species. Many violets have two different kinds of flowers. In the springtime they produce the familiar white or blue flowers ; but later in the year they bear a second crop of flowers which are minute and bud-like, and incapable of opening. These closed flowers pollinate themselves and are hence said to be cleistogamuc. CARYOPHYLLACEZ: (Pink Family) Herbs. Leaves opposite. Inflorescence cymose. Flowers regular, cyclic, hypogynous. Sepals four or five. Petals four, five (or none), polypetalous. Stamens usually eight or ten, often obdiplostemonous, usually hypogynous. Carpels from two to five, syncarpous, superior; ovary one-chambered: ovules many, on a central placenta; styles from two to five. Seed perispermic, embryo curved. Type I.: CHICKWEED (SteWaria media). Vegetative Characters.—Annual herb; much branched in a cymose manner (fig. 43). Note the line of hairs on one side of each internode, continuous with a fringe of hairs on the bases of the leaves. Leaves opposite, exstipulate, simple, entire; lower leaves stalked, upper leaves sessile. Inflorescence axillary, commences as a two-branched cyme (dichasium). Flower (fig. 159) § regular, cyclic; small, white. The flowers vary considerably, but a complete typical flower will be described first, and then the variations will be noted. Sepals (cx) five, separate. Petals (co) five, separate. Note the deep division of each petal. Stamens 5+5, hypogynous. The stamens composing the outer whorl (af) are opposite to the petals: whilst the five inner stamens (as) alternate with them. The flower is therefore obdiplostemonous. Anthers POLYPETALA—CARYOPHYLLACE/ 131 introrse. /Vectaries (7) five, very small knobs standing outside the five inner stamens and, therefore, opposite the sepals. Fig. 159.—Vertical section of flower of Stellaria media. Carpels three, syncarpous, superior: styles three: ovary (ov) one-chambered, with many ovules on a central placenta. Fruit (fig. 124) a capsule, opening by six valves. Seed (fig. 117) small, kidney-shaped, with perisperm. Variations in the flower.—The sepals and carpels remain constant in number (ex- cepting that very rarely the sepals may be six in number). In some flowers the five stamens which should be opposite the petals are wanting: in others there are only three stamens, which are opposite three sepals : in still other flowers no stamens are present, so that the flower is carpellary. Again, in some cases the petals are wanting. Pollin- ation.—The plants are found in flower throughout the year. The honey is accessible to — J e Co S wf me © 4 D a Sa Fig. 160.—Floral diagram of Stellaria media. short-tongued insects, and the flowers are cross - pollinated 132 DICOTYLEDONS by the agency of many kinds of insects (bees, beetles, flies, etc.). Self-pollination often takes place in open flowers, because the stigmas come in contact with the anthers; but it also occurs in flowers which remain closed. These closed self- pollinating flowers are merely ordinary flowers which fail to open ; they are not reduced and altered as are the cleistogamic flowers of the Violet. OTHER Types: PINK (Dianthus): CATCHFLY (Silene): CAMPION (Lychnis). The flowers of these plants differ from those of the Chick- weed more particularly in having a tubular gamosepalous calyx and long-clawed petals. “Their honey is consequently con- cealed at the bottom of a long tube, and cannot be reached by short-tongued insects. These flowers are exclusively pollinated by insects with long tongues—z.e. mainly by butterflies and moths. The comparison between these flowers and those of Stellaria gives us additional evidence for the view that the shapes of insect-pollinated flowers bear relation to the sorts of insects which pollinate them (see pages 81, 82 and 119-121). It is important to note that Pinks are pollinated by butterflies flying during the daytime, and that they often have a pink colour and delicious scent. Contrast this with the white colour of the flowers of Lychnis vespertina, which open at dusk, give out their strongest scent at that time, and are pollinated by night- flying moths. The white colour renders flowers more conspicuous at night. MALVACEZ (Mallow Family) Herbs or shrubs. Leaves alternate, stipulate. Flowers regular, hypogynous, often showy. Sepals five, gamosepalous, valvate. Petals five, nearly polypetalous, joined to the stamens at the base. Stamens numerous, filaments united. Anthers with only two pollen-sacs each. Carpels from three to 0, syncarpous (or apocarpous). Ovary with from three to many chambers. Type: MALLOWS (Malwa sylvestris and M. rotundifolia). These two species may be treated together, as they are very similar. POLYPETALA—MALVACE/ 133 Vegetative characters.—Herbs with hairs. Leaves alternate, stipulate, simple, palmately-veined, lobed, margins scalloped. The leaves are folded in the bud. Inflorescence, axillary tufts 162 161 163 Fig. 161.—Vertical section of flower of Malva sylvestris. Fig. 162.—Upper part of stamen of ditto, showing dehiscence of anther. Fig. 163.—Portion of flower of ditto, showing calyx, epicalyx bc), and part of style : the stamens and petals are removed. too complicated for description here. Three bracts close beneath the calyx form an involucre, which is known as the epicalyx (dc). Flower (fig. 161) actinomorphic &%, cyclic, showy. Sepals (sp) five, combined, valvate in the bud. Vectaries five pits on the bases of the five sepals, protected by hairs on the margins of the bases of the petals. Petals five, contorted in the bud. The petals are united to one another and to the stamens by their bases. Stamens numer- ous, united by their filaments to form a tube (col), epi- petalous. The numerous stamens are in reality produced by a branching of five stamens placed opposite the five petals. Each anther has only two pollen-sacs, and represents only half a complete anther; it is kidney-shaped (fig. 162). Carpels (figs. 161, 163) several, syncarpous, superior. Ovary (ov) 134 DICOTYLEDONS © with several chambers, each representing one carpel and containing one ovule attached to the axile placenta. . Style (s¢) one, which divides above into as many branches as there are carpels and ovary-chambers: each branch of the style is stigmatic on its inner and upper surface. Fruit (fig. 164) a schizocarp splitting into one-seeded cocci (cc). Pollination. —In both these species of Mallows the stamensripen before the carpels, and their opened anthers form a group round the closed erect style-branches. As the stigmas ripen and commence to separ- ate, the filaments gradually bend backwards and outwards. In JZ. sylvestris the anthers are Fig. 164.—Fruit of Malva sylvestris : carried completely out of reach se= sepals; ¢c= cocci. of the stigmas, so that the flower cannot pollinate itself. But in AZ rotundifolia the anthers are not borne so far backwards, whilst the style- branches gradually curl over and bring the stigmas into contact with the open anthers: thus the flower can regularly pollinate itself. The flowers of JZ. sylvestris are more showy, and are visited more frequently by insects which cause cross-pollination. Thus we see that of these two flowers which are so much alike, the more conspicuous is more frequently visited by insects, and consequently more extensively cross-pollinated. This tends to prove that conspicuousness of flowers aids in attracting insects. On the other hand, the less conspicuous flower of MZ. rotun- difolia is more often self-pollinated. This fact goes to show that the more perfectly cross-pollination by insects is ensured, the more precautions are taken to avert self-pollination ; and that, on the other hand, when cross-pollination is not ade- quately secured, the flower makes provision for the formation of seeds by self-pollination. Putting both results together, we see that flowers are conspicuous in order to attract insects which shall effect cross-pollination. POLYPETALA—GERANIACE 135 GERANIACEA (Geranium Family) Herbs with stipulate leaves. Flowers usually regular, hypogynous. Sepals five. Petals five, polypetalous. Stamens 5+5, obdiplostemonous, or only five; filaments slightly united at their bases. Carpels five, syncarpous ; ovary, five- chambered. Fruit possessing a “beak.” Type: HERB ROBERT (Geranium robertianum). Vegetative characters._Herb, strongly scented, erect or spreading. Leaves alternate, stipulate, simple, deeply divided. The leaf is in the first place incompletely divided into three Fig. 165.—Vertical section ot flower of Herb Robert. primary divisions, thus showing that the venation is essentially palmate, though the finer nerves are pinnate. Branching and Infiorescence.—The branching at the summit of the stem is cymose: the primary method of branching is forked (dichasium), but the subsequent branches are monochasia. The flowers are ultimately arranged in pairs. Each pair represents a mono- chasium with a terminal flower and a lateral flower which arises in the axil of the larger of the two prophylls of that axis. Flower (fig. 165) actinomorphic, %, cyclic: purplish-red. DICOTYLEDONS Sepals (s) five, imbricate. Petals (f) five, separate. Stamens 5 +5, with their filaments slightly combined at their bases. an The stamens (fa) forming the outer whorl are opposite the petals (obdiplostemonous) and are shorter than those (sa) op- posite the sepals ; anthers, in- trorse. JVectaries (m) five lamps opposite the sepals, and lying 5 between them and thefiveinner stamens. Carpels five, syncar- pous, superior. Ovary (oz) five- lobed, five-chambered: each chamber contains two ovules attached to the axile placenta. ~ 4 Style single, but dividing above into five branches with stig- Fig. 166.—Floral diagram of Herb Robert. yas (sg). Itis important tonote that the ovary-chambers and five style-branches are opposite to the petals. Thus the five carpels are opposite to the petals instead of being opposite to the sepals: this is an additional peculiarity of many obdiplostemonous flowers. Fruit (fig. 167).—The main single part of the style elongates, and becomes a strong “beak.” Only one ovule in each chamber forms a seed. When the fruit is ripe, as it dries, the five carpels separate, one by one or simultaneously, from below upwards in such a manner that the five seed - containing chambers (cocci) are carried up by elastically curling strips of the “beak,” and are thrown off. The fruit is a peculiar schizocarp, because the carpels do _ not open whilst still attached to the mother-plant. In some of the British species of Geranium the Fig- 167-—Fruit of Herb Robert. POLYPETALZ—PAPILIONACE 137 carpels open, and the seeds are violently thrown out as the strips of the beak contract, so that their fruits are explosive capsules. OXALIDACEZ (Woodsorrel Family) This family is often included in the Geraniacee. The typical floral formula is the same in both families K5 C5 A5+5 G(5). The Oxalidacez differ from Geranium in the following respects :—(i.) The leaves are compound. (ii.) Often there are more than two ovules in each of the five chambers of the ovary. iii.) There are five styles. (iv.) The capsular fruit has no “beak.” TyPpE: WOODSORREL (Oxals acetoselia). Herb with a rhizome, which is a true axis and not a sympode. The leaves are compound, digitate, with three leaflets. Note their day- and night- movements (figs. 249, 250). Inflorescence is cymose. Flowers @ white. (i.) The petals are contorted in the bud. (ii.) The five nectaries are opposite the petals, and lie between them and the five outer stamens. (iii.) The plant produces small cleistogamic flowers in addition to ordinary white ones. (iv.) The fruit is a capsule dehiscing along the dorsal sutures: the seeds are ejected violently from it by the elastic contraction of a white fleshy coat which envelops each seed separately like an outer testa. PAPILIONACEZ (Pea Family). Herbs or shrubs. Leaves alternate, stipulate, usually com- pound. Flowers irregular, cyclic, weakly perigynous. Sepals five, gamosepalous. Petals five, polypetalous, consisting of a standard, two wings, and a keel. Stamens ten, weakly perigynous; filaments of all, or of all but one, combined. Carpel one, superior. Fruit usually a legume. Seed non- endospermic. Types: GARDEN PEA (Pisum sativum): WHITE CLOVER (Zrifolium repens). Vegetative characters.— Herbs, with alternate compound stipulate leaves. The Clover is a creeping perennial, its leaves (figs. 251, 252) having three leaflets and two small stipules 138 DICOTYLEDONS each. The pea is a climbing annual with pinnate leaves (fig. 59) and large green persistent stipules (); some of the leaflets are converted into tendrils (47). Inflorescences axillary: capitulum in the clover; peculiar, two-flowered in the pea. Flowers (figs. 96, 97) median-zygomorphic, irregular, 8, cyclic, perigynous. Sefa/s five, combined to form a five- toothed cup. /éetals five, polypetalous, irregular. The posterior petal (sd) is the largest, and is termed the standard a. ; the two lateral petals (w) are termed the wings ale) ; whilst the two anterior petals (4), which have separate claws, cohere by their blades, and form the boat-shaped keel (carina). The estivation (fig. 101) is descending-imbricate (see page 73). Stamens (fig. 87) ten, weakly perigynous. The single posterior stamen (fa) is separate, but the filaments of the nine others cohere to form a tube (az. ¢), which is open only along its: posterior face (as well as at the summit). Though the ten stamens represent two whorls of five each, all ten are inserted at the same level on the receptacle. The stamens lie hidden inside the keel, and they in turn conceal the single ovary. The base of the inner face of the staminal tube acts as a mectary. Carpel one, superior; ovary (ov) one- chambered, bearing a double line of ovules on the parietal placenta; style one; stigma (sg) simple. Fruit (fig. 119g), a legume. Seeds non-endospermic. Pollination.—Like the flowers of all the Papilionacez, these flowers are specially con- structed for pollination by means of bees. The bee alights on the flower in such a way as to use the ale asa platform. This depresses the ale, which in turn drag the keel (carina) down. In this manner the upwardly directed stigma and the pollen inevitably come into contact with the under-surface of the bee’s body. The bee thrusts its tongue into the slit on the upper (posterior) face of the staminal tube and sips the honey which accumulates between the base of the ovary and the base of the staminal tube. When the bee flies away, the two alze and the keel rise up again and assume their former positions. The bee, visiting flower after flower, may thus effect cross-pollination. The flowers may self-pollinate themselves. In these flowers we may note: (i.) How completely the alee and carina protect the honey and pollen from rain and marauding insects. (ii.) The honey can only be reached from above (from the posterior face of the staminal: column). (iii.) The alz, when forced down, POLYPETALACA—ROSACE 139 drag the carina with them, because they are inter-locked with (e.g. Pea), or actually joined to (e.g. Clover), the sides of the carina. [Try and see what causes the wings and keel to return to their places when the pressure of the bee is removed. ] OTHER TYPES OF PAPILIONACE. In the flower of the Broom and some other Papilionacez the filaments of all ten stamens are joined together, but there still remains a small window-like opening on each side of the base of the posterior stamen. These two openings render the honey accessible to bees. The White Clover has a creeping stem ; the Broad Bean (Vicia faba) is an erect plant; the Pea, Vetches, and others climb by tendrils, which are modified leaflets ; whilst the Scarlet Runner (Phaseolus) has a twining (left-handed) stem by which it climbs erect slender supports. The Papilionaceze have on their roots peculiar swellings or tubercles, which are caused by microscopic fungi. The com- pound leaves of many types display day- and night- movements. ROSACEAE (Rose Family) Herbs or shrubs. Leaves usually alternate, stipulate. Flowers regular, usually perigynous. Sepals usually 4 or 5. Petals usually 4 or 5, polypetalous. Stamens usually numerous, bent inwards in the bud. Carpels, from x to o, usually apocar- pous, usually superior; styles more or less separate; often I or 2 ovules in each carpel. Fruit various. Seeds with very little or no endosperm. Type I: DOG ROSE (Rosa canina).* Vegetative characters.—Shrub, with numerous prickles, which are “subsidiary outgrowths.” Leaves alternate, with persistent stipules, pinnately compound with a_ terminal leaflet ; margins of the leaf saw-like (serrate). Inflorescence terminal; the flower terminates a branch; in addition, one or two subjacent bracts may have a flower in the axil of each. [Look for the transitions between the foliage-leaves and bracts. ] Flower (fig. 168) actinomorphic, %, cyclic; coloured and scented. Sepals (cal) five.. The sepals are imbricate in the bud. The two external sepals have “beards” on both lateral * Any Rose, save a double variety, may be selected for examination. 140 DICOTYLEDONS margins; a third sepal has one exposed margin which is AKIN) SNe. NE Loa Qh WZ ] 168 169 Fig. 168.—Vertical section of flower of Dog Rose. Fig. 169.—A carpel of ditto, with the ovary cut down the centre, bearded, and the other margin concealed and not bearded (entire); finally, the fourth and fifth sepals are completely overlapped by the others, and have both margins even. Petals (cor) five, separate. Stamens (and) numerous, perigynous, curved inwards in the flower-bud. Receptacle (rc) [often termed the calyx-tube] deeply hollowed, so as to be urn-shaped, with its opening narrowed above. The sepals, petals, and stamens are inserted round the margin ‘of the opening ; they are all perigynous. A disk (d) clothes the lips and coats the lining of the receptacle-tube above the insertion of the carpels. The disk has not been seen to pour out honey. Cargels numerous, apocarpous ; the many separate i ovaries (ov) are concealed inside tube _ Fig. 170.—Vertical sec- of the receptacle, and are inserted on its hy RoomPound Mut of base and sides. They are superior, because of a simple fruit; ss= 3 ee i A testa of d3e= they are not indistinguishably fused with fStycr seed; coomtne POLYPETALA—ROSACEE 141 the receptacle. Each one-chambered ovary (fig. 169, ov) contains one ovule (0), and is surmounted by a single style (s/), which emerges through the mouth of the receptacular tube and bears a simple stigma (sg). Fruit (fig. 170) compound, con- sisting of numerous achenes concealed in the red hollowed receptacle, which bears a persistent calyx. (Each achene is, of course, developed from one of the separate carpels.) Seeds having no endosperm. Dissemination—The achenes are scattered by the agency of birds, which peck at the red receptacle and incidentally dislodge the achenes. The red colour serves to render the fruit easily visible to birds. Tyre II.: STRAWBERRY (/ragaria vesca). The floral formula is the same as for the Rose, K5 C5 Aoo Goo, Beneath the calyx, and alternating with the sepals, is a whorl of sepal-like members which forms an epicalyx (fig. 82). The epicalyx represents, in this case, the stipules of the sepals, which have joined .- together in pairs. The shape of the receptacle * . a is curious (compare fig. 173, representing the fy Blackberry flower), it is like a shallow saucer (7c) S with a large lump (7d) rising from its centre. eek The sepals, petals, and stamens are attached to carpelofStraw- the rim of the saucer, and are therefore perigynous. [i1"¥, spowing Numerous apocarpous carpels are inserted on the down ‘the central outgrowth. The disk (d) is like a ring, ™4* and lines the space between the rim of the saucer and the place of attachment of the central swelling ; it excretes honey, and is a nectary. Each carpel (fig. 171) has its style (sy) attached to the side of the ovary (ov). The ovary contains one ovule (0). Fruit (fig. 172).— After pollination, the central mass of the receptacle (7c) enlarges greatly, becomes first white in colour, and finally changes into the red, sweet, juicy “strawberry” which we eat. Each carpel remains small Fig. 172—Vertical section of and forms an achene (ac) with one compound fruit of Strawberry. seed (s) inside it. The complete fruit of the Strawberry is compound, and consists of many achenes 142 DICOTYLEDONS inserted upon an enlarged fleshy receptacle, to which the calyx (sp) and epicalyx (ef) still adhere. Dissemination.—The fruits are dispersed by birds, which eat the juicy receptacle and incidentally swallow the little dry achenes. These achenes have indigestible hard pericarps, and consequently pass uninjured through the bird’s body. Vegetative characters (fig. 54).— Note the “runners,” also the stipulate leaves with three leaflets. Types III.: BLACKBERRY (Rubus fruticosus) AND RASPBERRY (ubus deus). The flowers (fig. 173) are structurally very like those of the Strawberry, the only important distinctions being that there is Sg ~ SZ gut OM gy “at : Hh 173 174 Fig. 173.—Vertical section of flower of Blackberry (in the figure, the ue part of the receptacle (7f) is drawn more spherical than it is in reality). Fig. 174.—Cross-section of a single ovary of ditto. no epicalyx, and the carpels contain two ovules each (fig. 174). After pollination the behaviour is different, however. The central outgrowth (7) of the receptacle which bears the carpels does not develop into a large fleshy mass ; it remains relatively small. But the carpels enlarge considerably and become one-seeded stone-fruits (drupes), which conceal the receptacular lump in their midst. Thus the fruit (fig. 175) of the Blackberry or Raspberry is compound: it consists of a collection of small stone-fruits (¢) inserted upon a receptacle which bears"also a persistent calyx (sf). Dissemination.—The POLYPETALA'—ROSACEA 143 fruits are distributed by birds in the same manner as in the 176 Fig. 175.—Vertical section of compound fruit of Blackberry : sp=sepals ; st=shrivelled stamens; d=drupes. Fig. 176.—Vertical section of a single drupe of ditto: end =stony layer of pericarp; ¢s=testa of the seed; cof=coty- ledons. Strawberry, but the stony endocarps (fig. 176, ed) protect the seeds. Types IV.: CHERRY, PLUM, anp APRICOT (Prunus). Prunus (including the Cherry, Plums, and Apricot) has flowers (fig. 177) constructed on the same plan as those of the Rose; but there is only one carpel, containing two ovules, at the bottom of the deep -receptacular tube (rc) of each flower. After pollination great differences in the behaviour of Prunus and of the Rose set in. The receptacle-tube of Prunus drops off, and the _ single Y , : 1 o} Fig. 177.—Vertical section f flower of Cherry. carpel grows greatly and becomes a one-seeded stone-fruit 144 DICOTYLEDONS (drupe) (fig. 128). Thus the fruit is simple, and consists of one drupe. The stipules of Prunus are not persistent, but drop off. TABLE SHOWING SOME DISTINCTIONS BETWEEN DIFFERENT SPECIES oF Prunus. I. Leaves rolled } Plums (Prunus domestica), (a) Fruit smooth, with ce ” (convolute) Bloom: in the bud. (4) Fruit velvety, yellow.—Apricot (Pranus arimeniaca). (a) Fruit black, red, or yellow smooth, }Cherry (Prunus cerasus). ee eae este | __without “bloom.” greenish, usually (A smooth variety of the Peach is in the bud. (4) Fruit more or ay Peach (Prunus persica), velvety. known as the Nectarine.) Types V.: APPLE anp PEAR (Pyrus): VI.: HAWTHORN (Crategus). The genus Pyrus includes both Apples and Pears. The flower (fig. 178) of Pyrus possesses five sepals (cx), five petals (cor), numerous stamens (a), and usually five carpels (fig. 179 es Not only is the receptacle (7c) hollowed to form a cup (as in the Rose), but the outer faces of the carpels are fused with the lining of the receptacle-tube. Thus the flower is markedly epigynous. The five carpels are also united to one another by their sides, and, at the most, are only free from each other along their ventral sutures and styles; consequently, a five-chambered inferior ovary is produced. In the flower of the Pear the five styles are separate, but in the Apple the styles are united at their bases. Each of the five ovary-chambers contains not more than two ovules. As the fruit (figs. 180, 181, 182) ripens, the lining of each chamber of the ovary becomes a parchment-like endocarp (¢). The portion (7c) lying outside this core of five endocarps enlarges greatly, and is responsible for the production of the large, fleshy part of the Apple or Pear fruit. The fruit is a peculiar inferior fruit known as a pome. Dissemination.—The fruits are adapted 180 181 Figs. 178-181.—Apple. Fig. 178.— Vertical section of flower. Fig. 180.—Ditto of fruit. Fig. 179.—Cross-section of ovary. Fig. 181.—Ditto of fruit. 145 K 146 DICOTYLEDONS. to invite the visits of fruit-eating beasts, which inadvertently “th swallow the seeds as they eat the fleshy a parts of the fruit. The Hawthorn (Crategus oxyacantha) “ts has flowers very similar in plan to those of the Apple and Pear; but the ovary /_. consists of two carpels only, and has cot two chambers. In the fruit the endocarp around each chamber becomes hard and stony (not parchment-like), so that the fruit is a stone-fruit with two stones. Wena eee onparchment- Birds are responsible for the distribu- ike chamber removed from z : . fruit of apple, containing a tion of these red fruits, which are ar eda of seed 5