Qk47 sh | [400 ALBERT R. MANN LIBRARY NEW YORK STATE COLLEGES OF AGRICULTURE AND HOME ECONOMICS AT CORNELL UNIVERSITY St, Vp, (Carb __ DATE DUE DEMCO 38-297 csr University Library Ti ae TWENTIETH CENTURY TEXT-BOOKS EDITED BY A. F. NIGHTINGALE, Pu. D. SUPERINTENDENT OF HIGH SCHOOLS, CHICAGO AND CHARLES H. THURBER, A. M. ASSOCIATE PROFESSOR OF PEDAGOGY IN THE UNIVERSITY OF CHICAGO TWENTIETH CENTURY TEXT-BOOKS Pie y Ne A TEXT-BOOK OF BOTANY BY JOHN M. COULTER, A.M., Pu. D. HEAD OF DEPARTMENT OF BOTANY UNIVERSITY OF CHICAGO NEW YORK D. APPLETON AND COMPANY 1900 (@ GRY] CS |4 00 CopyRIGHT, 1899 By D. APPLETON AND COMPANY Citi Pind NLS A TEXT-BOOK OF BOTANY PREFATORY NOTE AutHovenH Plant Relations and Plant Structures have been prepared as independent volumes, chiefly to meet the needs of those schools which can give but one half year to Botany, they form together a natural introduction to the science. With this in view, the simple title Plants seems suitable, with the understanding that this volume is an introduction to the study of plants. . Either part of this combined volume may be used first, according to the views or needs of the teacher. In many cases it may be wise not to observe the order of the book, but to organize laboratory work as seems best, and to assign the appropriate readings wherever they may occur in the volume. The author isa stickler for independent teaching, and would not presume to prescribe an order or a method for teachers. His purpose is simply to offer those facts and suggestions which may be helpful to them in organizing and presenting their work. He would urge that intelligent contact with plants is the essential thing; that a clear understanding of a few large facts is better than the collec- tion of numerous small ones; and that “ getting through” should never sacrifice the leisure needed for digestion. The two parts of this work are indexed separately, and references to indexes are to be made at the end of each part. Joun M. Counter. Tue University or Cutcaco, November, 1899. TWENTIETH CENTURY TEXT-BOOKS PLANT RELATIONS A FIRST BOOK OF BOTANY BY JOHN M. COULTER, A.M., Px.D. HEAD PROFESSOR OF BOTANY UNIVERSITY OF CHICAGO NEW YORK D. APPLETON AND COMPANY 1900 COPYRIGHT, 1899, By D. APPLETON AND COMPANY. PREFACE. THE methods of teaching botany in secondary schools are very diverse, and in so far as they express the experience of successful teachers, they are worthy of careful considera- tion. As the overwhelming factor in successful teaching is the teacher, methods are of secondary importance, and may well vary. Itis the purpose of the present work to contribute another suggestion as to the method of teach- ing botany in secondary schools. The author does not intend to criticise other methods of teaching, for each teacher has his own best method, but it may be well to state the principles which underle the preparation of this work, The botany is divided into two parts, each representing work for half a year. The two books are independent, and opinions may differ as to which should precede. The first book, herewith presented, is dominated by Ecology, and also contains certain fundamentals of Physiology that are naturally suggested. The second book will be domi- nated by Morphology, but plant structure, function, and classification will be developed together in an attempt to trace the evolution of the plant kingdom. In the judg- ment of the author Ecology should precede Morphology, but this order brings to Ecology no knowledge of plant structures and plant groups, which is of course unfortu- nate. The advantages which seem to overbalance this dis- advantage are as follows: 1. The study of the most evident life-relations of plants gives a proper conception of the place of plants in 1* vi PREFACE. nature, a fitting background for subsequent more detailed studies. 2. Such a view of the plant kingdom is certainly of the most permanent value to those who can give but a half year to botany, for the large problems of Ecology are con- stantly presented in subsequent experience, when details of structure would be forgotten. 3. The work in Ecology herein suggested demands Lt- tle or no use of the compound microscope, an instrument ul adapted to first contacts with nature. The second book will demand the use of the compound microscope, and those schools which possess such an equip- ment may prefer to use that part first or exclusively. In reference to the use of this part something should be said, although such cautions are reiterated in almost every recent publication. .A separate pamphlet containing “Suggestions to Teachers” who use this book has been prepared, but a few general statements may be made here. This book is intended to present a connected, readable account of some of the fundamental facts of botany, and may serve to give a certain amount of information. If it performs no other service in the schools, however, its pur- pose will be defeated. It is entirely too compact for any such use, for great subjects, which should involve a large amount of observation, are often merely suggested. It is intended to serve as a supplemeut to three far more im- portant factors: (1) the teacher, who must amplify and suggest at every point; (2) the laboratory, which must bring the pupil face to face with plants and their strue- tures; (3) field-work, which must relate the facts observed in the laboratory to their actual place in nature, and must bring new facts to notice which can be observed nowhere else. Taking the results obtained from these three fac- tors, the book seeks to organize them, and to suggest explanations. It seeks to do this in two ways (1) dy means of the tect, which is intended to be clear and un- PREFACE. vii technical, but compact ; (2) dy means of the illustrations, which must be studied as carefully as the text, as they are only second in importance to the actual material. Espe- cially is this true in reference to the landscapes, many of which cannot be made a part of experience. Thanks are due to various members of the botanical staff of the University, who have been of great service in offering suggestions and in preparing illustrations. In this first book I would especially acknowledge the aid of Professor Charles R. Barnes and Dr. Henry C. Cowles. The professional botanist who may critically examine this first book knows that Ecology is still a mass of incho- ate facts, concerning which we may be said to be making preliminary guesses. It seems to be true, nevertheless, that these facts represent the things best adapted for pres- entation in elementary work. The author has been com- pelled to depend upon the writings of Warming and of Kerner for this fundamental material. From the work of the latter, and from the recent splendid volume of Schim- per, most useful illustrations have been obtained. The number of original illustrations is large, but those obtained elsewhere are properly credited. Joun M. COULTER. Tae University or Curcaco, /ay, 1899. CONTENTS. CHAPTER, I.—INTRODUCTION . é ‘ : ‘ : T].—Fo.iack LEAVES: THE LIGHT-RELATION If{]..—FoulaGe LEAVES: FuNcTIoN, STRUCTURE, AND PROTECTION 1V.—Snoots V.—Roors VI.—REPRODUCTIVE ORGANS VIT.—FLoweERS AND INSECTS VITIL.—AN INDIVIDUAL PLANT IN ALL OF ITS RELATIONS IX.—THE STRUGGLE FOR EXISTENCE X.—THE NUTRITION OF PLANTS XI.—PLANT SOCIETIES : EcoLOGICAL FACTORS AXITT.—HypDRoPHYTE SOCIETIES ‘ . XIITI.—XeEROPHYTE SOCIETIES 2 é ri XIV.—MEsoPpHYTE SOCIETIES 5 7 XV.—HALOPHYTE SOCIETIES a‘ : < : InDEX : ) ‘ : 3 e ‘ ; 5 - PAGE, BOTANY PART I.—PLANT RELATIONS CHAPTER I. INTRODUCTION. 1. General relations.—Plants form the natural covering of the earth’s surface. So generally is this true that a land surface without plants seems remarkable. Not only do plants cover the land, but they abound in waters as well, both fresh and salt waters. They are wonderfully varied in size, ranging from huge trees to forms so minute that the microscope must be used to discover them. They are also exceedingly variable in form, as may be seen by comparing trees, lilies, ferns, mosses, mushrooms. lichens, and the green thready growths (a/g@) found in water. 2. Plant societies—One of the most noticeable facts in reference to plants is that they do not form a monotonous covering for the earth’s surface, but that there are forests in one place, thickets in another, meadows in another, swamp growths in another, ete. In this way the general appear- ance of vegetation is exceedingly varied, and each appear- ance tells of certain conditions of hving. These groups of plants living together in similar conditions, as trees and other plants ina forest, or grasses and other plants in a meadow, are known as plunt societies, These societies are as 2 PLANT RELATIONS. numerous as are the conditions of living, and it may be said that each society has its own special regulations, which ad- mit certain plants and exclude others. The study of plant societies, to determine their conditions of living, is one of the chief purposes of botanical field work. 3. Plants as living things—Before engaging in a study of societies, however, one must discover in a general way how the individual plant lives, for the plant covering of the earth's surface is a living one, and plants must always be thought of as living and at work. They are as much alive as are animals, and so far as mere living is concerned they live in much the same way. Nor must it be supposed that animals move and plants do not, for while more animals than plants have the power of moving from place to place, some plants have this power, and those that do not can move cer- tain parts. The more we know of living things the more is it evident that life processes are alike in them all, whether plants or animals. In fact, there are some living things about which we are uncertain whether to regard them as plants or animals. 4, The plant body.—Every plant has a body, which may be alike throughout or may be made up of a number of different parts. When the green thready plants (alge), so common in fresh water, are examined, the body looks like a simple thread, without any special parts ; but the body of a lily is made up of such dissimilar parts us root, stem, leaf, and flower (see Figs. 75, 144, 155, 169). The plant without these special parts is said to be simple, the plant with them is called complex. The siniple plant lives in the same way and does the same kind of work, so far as living is concerned, as docs the complex plant. The differ- ence is that in the case of the simple plant its whole body does every kind of work; while in the complex plant different kinds of work are done by different regions of the body, and these regions come to look wnlike when differ- ent shapes are better suited to different work, as in the INTRODUCTION. 3 case of a leaf and a root, two regions of the body doing different kinds of work. 5. Plant organs—These regions of the plant body thus set apart for special purposes are called organs. The sim- plest of plants, therefore, do not have distinct organs, while the complex plants may have several kinds of organs. All plants are not either very simple or very complex, but beginning with the simplest plants one may pass to others not quite so simple, then to others more complex, and so on gradually until the most complex forms are reached. This process of becoming more and more complex is known as differentiation, which simply means the setting apart of different regions of the body to do different kinds of work. The advantage of this to the plant becomes plain by using the common illustration of the difference between a tribe of savages and a civilized community. The savages all do the same things, and each savage does everything. In the civilized community some of the members are farmers, others bakers, others tailors, others butchers, etc. This is what is known as “ division of labor,” and one great advan- tage it has is that every kind of work is better done. Dit- ferentiation of organs in a plant means to the plant just what division of labor means to the community ; it results in more work, and better work, and new kinds of work. The very simple plant resembles the savage tribe, the com- plex plant resembles the civilized community. It must be understood, however, that in the case of plants the differ- entiation referred to is one of organs and not of individuals. 6. Plant functions—Whether plants have many organs, or few organs, or no organs, it should be remembered that they are all at work, and are all doing the same essential things. Although many different kinds of work are being carried on by plants, they may all be put under two heads, nutrition and reproduction. Every plant, whether simple or complex, must care for two things: (1) its own support (nutrition), and (2) the production of other plants like 4 PLANT RELATIONS. itself (reproduction). To the great work of nutrition many kinds of work contribute, and the same is true of repro- duction. Nutrition and reproduction, however, are the two primary kinds of work, and it is interesting to note that the first advance in the differentiation of a simple plant body is to separate the nutritive and reproductive regions. In the complex plants there are nutritive organs and reproductive organs ; by which is meant that there are distinct organs which specially contribute to the work of nutrition, and others which are specially concerned with the work of reproduction. The different kinds of work are conveniently spoken of as functions, each organ having one or more functions. 7. Life-relations—In its nutritive and reproductive work the plant is very dependent upon its surroundings. It must receive material from the outside and get rid of waste material ; and it must leave its offspring in as favorable conditions for living as possible. As a consequence, every organ holds a definite relation to something outside of it- self, known as its life-relation. For example, green leaves are definitely related to light, many roots are related to soil, certain plants are related to abundant water. some plants are related to other plants or animals (living as parasites), etc. A plant with several organs, therefore, may hold a great variety of life-relations, and it is quite a complex problem for such a plant to adjust all of its parts properly to their necessary relations. The study of the life-relations of plants is a division of Botany known as Ecology, and presents to us many of the most important problems of plant life. It must not be supposed that any plant or organ holds a perfectly simple life-relation, for it is affected hy a great variety of things. A root, for instance, is affected by light, gravity, moisture, soil material, contact, etc. Every or- gan, therefore, must adjust itself to a very complex set of life-relations, and a plant with several organs has so many INTRODUCTION. 5 delicate adjustments to care for that it is really impossi- ble, as yet, for us to explain why ull of its parts are placed just as they are. In the beginning of the study of plants, only some of the most prominent functions and life-rela- tions can be considered. In order to do this, it seems bet- ter to begin with single organs, and afterwards these can be put together in the construction of the whole plant. CHAPTER II. FOLIAGE LEAVES: THE LIGHT-RELATION. 8. Definition—A foliage leaf is the ordinary green leaf, and is avery important organ in connection with the work of nutrition. It must not be thought that the work done by such a leaf cannot be done by green plants which have no leaves, as the algw, for example. A leaf is simply an or- gan set apart to do such work better. In studying the work of a leaf, therefore, we have certain kinds of work set apart more distinctly than if they were confused with other kinds. For this reason the leaf is selected as an in- troduction to some of the important work carried on by plants, but it must not be forgotten that a plant does not need leaves to do this work ; they simply enable it to work more effectively. 9. Position It is easily observed that foliage leaves grow only upon stems, and that the stems which bear them always expose them to light; that is, such leaves are aerial rather than subterranean (see Figs. 1, 75,169). Many stems grow underground, and such stems either bear no foliage leaves, or are so placed that the foliage leaves are sent above the surface, as in most ferns and many plants of the early spring (see Figs. £5, 46, 144). 10. Color.—Another fact to be observed is that foliage leaves have a characteristic green color, a color so universal that it has come to be associated with plants, and espe- cially with leaves. It is also evident that this green color holds some necessary relation to light, for the leaves of plants grown in the dark, as potatoes sprouting in a cellar, FOLIAGE LEAVES: THE LIGHT-RELA'TION. 7 do not develop this color. Even when leaves have devel- oped the green color they lose it if deprived of light, as is shown by the process of blanching cclery, and by the effect on the color of grass if a board has lain upon it for some time. It seems plain, therefore, that the green color found in working foliage leaves depends upon light for its existence. We conclude that at least one of the exseutial life-rela- tions of a foliage leaf is what may be called the light-rela- fion. his seems to explain satisfactorily why such leaves are not developed in a subterranean position, as are many stems and most roots, aud why plants which produce them do not grow in the dark, asin caverns. The sume green, and hence the sume light-relation, is observed in other parts of the plant as well, and in plants without leaves, the only difference being that leaves display it most conspicu- ously. Another indication that the green color is con- nected with light may be obtained from the fact that it is found only in the surface region of plants. If one cuts across a living twig or into a cactus body, the green color will be seen only in the outer part of the section. The con- clusion is that the leaf is a special organ for the lght-re- lation. Plants sometimes grow in such situations that it would be unsafe for them to display leaves, or at least large leaves. Insuch a case the work of the leaves can be thrown upon the stem. .\ notable illustration of this is the cactus plant, which produces no foliage leaves, but whose stem dis- plays the leaf color. 11. An expanded organ.—Another general fact in refer- ence to the foliage leaf is that in most cases it is an expanded organ. This means that it has a great amount of surface exposed in comparison with its mass. As this form is of such common occurrence it is safe to conclude that it is in some way related to the work of the leaf. and that whatever work the leaf doves demands an exposure of surface rather than thickness of body. It is but another step to say that 2 8 PLANT RELATIONS. the amount of work un active leaf can do will depend in part upon the amount of surface it exposes. THE LIGHT-RELATION, 12. The general relation —The ordinary position of the foliage leaf is more or less horizontal. This enables it to receive the direct rays of light upon its wpper surface. In Fig. 1. The leaves of this plant (7iews) are in general horizontal, but it will be seen that the lower ones are directed down- ward, and that the leaves hecome more horizontal as the stem is ascended. It will also be seen that the leaves are so broad that there are few vertical rows. this way more rays of light strike the leaf sur- face than if it stood ob- liquely or on edge. It is often said that leaf blades are so directed that the flat surface is at might angles to the iecident rays of light. While this may be true of horizon- tal leaves in a_ general way, the observation of almost any plant will show that it is a very general statement, to which there are numerous exceptions (see Fig. 1). Leaves must be arranged to receive as much light as possible to help in their work, but too much light will destroy the green substance (chloro- phyll), which is essential to the work. The adjust- ment to light, therefore, is a delicate one, for there must be just enough FOLIAGE LEAVES: THE LIGHT-RELATION. 9 and not too much. The danger from too much light is not the same in the case of all leaves, even on the same plant, for some are more shaded than others. Leaves also have « way of protecting themselves from too intense light by their structure, rather than by a change in their posi- tion. It is evident, therefore, that the exact position which any particular leaf holds in relation to ight depends upon many circumstances, and cannot be covered by a general rule, except that it seeks to get all the light it can without danger. 13. Fixed position.— Leaves differ very much in the power of adjusting their position to the direction of the light. Fie. 2. The day and night positions of the leaves of a member (Amicia) of the pea family.— After STRASBURGER. Most leaves when fully grown are in a fixed position and cannot change it, however unfavorable it may preye to he, except as they are blown about. Such leaves are said to have fixed light positions. This position is determined by the light conditions that prevailed while the leaf was grow- ing and able to adjust itself. If these conditions continue, the resulting fixed position represents the best one that can be secured under the circumstances. The leaf may not receive the rays of light directly throughout the whole period of daylight, but its fixed position is such that it probably receives more light than it would in any other position that it could secure. 10 PLANT RELATIONS. 14. Motile leaves— There are leaves, however, which have no fixed light position, but are so constructed that they can shift their position as the direction of the light changes. Such leaves are not in the same position in the afternoon as in the forenoon, and their night position may be very different from either (see Figs. 2, 5, 3b, £). Some of the common house plants show this power. In the cause of the com- mon Qralis the night Fie. 3a. The day position of the leaves of redbud position of the leaves (Cervis).—After ARTHUR. is remarkably different from the position in light. If such a plant is exposed to the light ina window and the positions of the leaves noted, and then turned half way around, so as to bring the other side to the light, the leaves may be observed to adjust them- selves gradually to the changed light-relations. Fic. 3b, The night position of the leaves 15. Compass plants.— A of redbud (Cervés),—After ARTHUR. striking illustration of a special light position is found in the so-called * compass plants.” The best known of these plants is the rosin-weed of the prairie region. Growing in situations exposed te intense light, the leaves are turned edeewise, the flat faces being turned away from the intense rays of midday, and directed towards the rays of less intensity ; that is, those of FOLIAGE LEAVES: THE LIGHT-RELATION. 11 . bY N N \ N iy we ST” ye Fig. 4. Two sensitive plants, showing the motile Jeaves. The plant to the left has its leaves and numerous leaflets expanded ; the one to the right shows the leaflets folded together and the leaves drooping.— After KERNER, the morning and evening (see Fig. 165). As a result, the apex of the leaf points in a general north or south direction. It is a significant fact that when the plant grows in shaded places the leaves do not assume any such position. It seems evident, therefore. that the position has something to do with avoiding the danger of too intense light. It 12 PLANT RELATIONS. must not be supposed that there is any ac- curacy in the north or south direction, as the edgewise position seems to be the signifi- cant one. In the ros- in-weed probably the north and south direc- tion is the prevailing one; but in the prickly lettuce, a very common weed of waste grounds, and one of the most striking of the compass plants, the edgewise position is frequently assumed without any special reference to the north or south direc- tion of the apex (see Fig. 5). 16. Heliotropism.— The influence of light upon the positions of leaves and other or- gans is known as /eli- otropism, and it is one of the most important of those external influ- ences to which plant organs respond (see Figs. 6, 43). Fie, 5. The common prickly lettuce (Lactuca It should be under- Scariola), showing the leaves standing edge- : ‘ : wise, and in a general north and south plane. stood cl early that this —After AnTHUR and MacDougau. is but a slight glimpse FOLIAGE LEAVES: THE LIGHT-RELATION, 13 Tia. 6. These plants are growing near a window. It will be noticed that the stems bend strongly towards the light, and that the leaves face the light. of the most obvious relations of foliage leaves to light, and that the important part which heliotropism plays, not only in connection with foliage leaves, but also in connection with other plant organs, is one of the most important and extensive subjects of plant physiology. RELATION OF LEAVES TO ONE ANOTHER. A. On erect stems. In view of what has been said, it would seem that the position of foliage leaves on the stem, and their relation to one another, must be determined to some extent by the necessity of a favorable light-relation. It is apparent that the conditions of the problem are not the same for an erect as for a horizontal stem. 17. Relation of breadth to number of vertical rows.— Upon an erect stem it is observed that the leaves are usu- 14 PLANT RELATIONS. ally arranged in a definite number of vertical rows. It is to the advantage of the plant for these leaves to shade one another as little as possible. Therefore, the narrower the leaves, the more numerous may be the vertical rows (see Figs. 7, 8); and the broader the leaves the fewer the vertical rows (xee Fig. 1), A relation exists, therefore, be- tween the breadth of leaves and the number of verti- cal rows, and the meaning of this becomes plain when the light-re- lation ix consid- ered. 18. Relation of length to the dis- tance between Fic. 7. An Easter lily, showing narrow leaves and leaves of the same numerous vertical rows. row.—The leaves in a vertical row may he close together or far apart. If they should be close together and at the same time long, it is evident that they will shade each other considerably, as the light cannot well strike in between them and reach the surface of the lower leaf. Therefore, the closer together the leaves of a verti- cal row, the shorter are the leaves; and the farther apart the leaves of a row, the longer may they be. Short leaves permit the light to strike hetween them cyen if they are close together on the stem; and long leaves permit the same thing only when they are far apart on the stem, A FOLIAGE LEAVES: THE LIGHT-RELATION. 15 relation is to be observed, therefore, between the length of leaves and their distance apart in the same vertical row. The same kind of relation cun be observed in reference to the breadth of leaves, for if leaves are not only short but narrow they can stand very close together. It is thus seen that the length and breadth of leaves, the number of ver- tical rows on the stem, and the distance between the leaves Fig. 8. A dragon-tree, showing narrow leaves extending in all directivns, and numer- ous vertical rows. of any row, all have to do with the light-relation and are answers to the problem of shading. 19. Elongation of the lower petioles—There is still another common arrangement by which an effective light- relation is secured by leaves which are broad and placed close together on the stem. In such a case the stalks (petioles) of the lower leaves become longer than those above and thus thrust their blades beyond the shadow (sce Fig. 9). It may be noticed that it is very common to 16 PLANT RELATIONS. find the lowest leaves of a plant the largest and with the longest petioles, even when the leaves are not very close together on the stem. It must not be supposed that by any of these devices shading is absolutely avoided. This is often impossible and sometimes undesirable. It simply means that by these Fie. 9. A plant (Seintpaulic) with the lower petioles elongated, thrusting the blades beyond the shadow of the upper leaves. A loose rosette. arrangements the most favorable light-relation is sought by avoiding too great shading. 20. Direction of leaves—Not only is the position on the stem to be observed, but the direction of leaves often shows a definite relation to light. It is a very common thing to find a plant with a cluster of comparatively large leaves at or near the ase, where they are in no danger of shading other leaves, and with the stem leaves gradually becoming FOLIAGE LEAVES: THE LIGHT-RELATION. 17 smaller and less horizontal toward the apex of the stem (see Figs. 10, 13). The common shepherd's purse and the mullein may be taken as illustrations. By this arrange- ment all the leaves are very completely exposed to the light. 21. The rosette habit.— The habit of producing a cluster or rosette of leaves at the base of the stem is called the rosette habit. Often this rosette of leaves at the hase, frequently lying flat on the ground or on the rocks, includes the only fo- liage leaves the plant pro- duces. It is evident that a rosette, in which the leaves must overlap one another more or less, is not a very favorable light arrange- ment, and therefore it must be that something is being Fie. 10. A plant (Echeveria) with fleshy provided for besides the leaves, showing large horizontal ones light-relation (see Figs. 1a at base, and: otis becomine, smaller ‘ . fea é and more directed upward as the 12, 13). What this is will sori ienecerdad. appear later. but even in this comparatively unfavorable light arrangement, there is evident adjustment to secure the most ight possible under the circumstances. The lowest leaves of the rosette are the longest, and the upper (or inner) ones become gradu- ally shorter, so that all the leaves have at least a part of the surface exposed to light. The overlapped base of such leaves is not expanded as much as the exposed apex, and hence they are mostly narrowed at the base and broad at the apex. This narrowing at the base is sometimes 18 PLANT RELATIONS. carried so far that most of the part which is covered is but a stem (petiole) for the upper part (blade) which is exposed. In many plants which do not form close rosettes a gen- Hie, 11. A eroup of live-for-evers, illustrating the rosette habit and the light-relation. In the rosettes it will be observed how the leaves are fitted together and diminish in size inwards, so that excessive shading is avoided. The individual leaves also become narrower where they overlap, andl are broadest where they are exposed to light. In the background is a plant showing leaves in very definite vertical rows. eral rosette arrangement of the leaves may be observed by looking down upon them from above (see Fig. 9), ax in some of the early buttercups which are so low that the large leaves would seriously shade one another, except that the lower leaves have longer petioles than the upper, and so reach beyond the shadow. FOLIAGE LEAVES: THE LIGHT-RELATION. 19 Fig. 12. Two clumps of roscttes of the house leek (Semperrirum), the one to the right showing the compact winter condition, the one to the left with rosettes more open after being kept indoors for several days. 22. Branched leaves.—Another notuble feature of foliage leaves, which has something to do with the lght-relation, is that on some plants the blade does not consist of one piece, but is lobed or even broken up into separate pieces. When the divisions are distinct they are called leaflets, and every gradation in leaves can be found, from distinct leaf- lets to lobed leaves, toothed leaves, and finally those whose margins are not indented at all (ev/irc). This difference in leaves probably has more important rea- sons than the light- relation, but its sig- nificance may be ob- served in this connec- tion. In those plants whose leaves are un- divided, the leaves generally either di- minish in size toward the top of the stem, or the lower ones de- Fie. 18. The leaves of a bellflower (Campanula), velop longer petioles. showing the rosette arrangement. The lower Bs tig Pevis petioles are successively longer, carrying their In this Cae the elt blades beyoud the shadow of the blades above. eral outline of the —After Kernen, dangerous shading, It will be seen that the larger blades or less-branched leaves are towards the bottom of the group, FOLIAGE LEAVES: THE LIGHT-RELATION. 21 plant is conical, a form very common in herbs with entire or nearly entire leaves. In plants whose leaf blades are broken up into leaflets (compound or branched leaves), however, no such diminution in size toward the top of the stem is necessary (see Fig. 17), though it may frequently a Teer Me ee Fig. 15. A plant showing much-branched leaves, which occur in great profusion with- out cutting off the light from one another. occur. When a broad blade is broken up into leaflets the danger of shading is very much less, as the light can strike through between the upper leaflets and reach the leaflets below. On the lower leaves there will be splotches of light and shadow, but they will shift throughout the day, so that probably a large part of the leaf will receive light at some time during the day (see Fig. 14). The 22 PLANT RELATIONS. general outline of such a plant, therefore, is usually not conical, as in-the other case, but cylindrical (sce Figs. 4, 15, 16, 22, 45, 83, 96, 155, 162, 169 for branched leaves). Many other factors enter into the light-relation of foli- age leaves upon erect stems, but those given may suggest Fie. 16. A cycad, showing much-branched leaves and palm-like habit. observation in this direction, and serve to show that the arrangement of leaves in reference to light depends upon many things, and is by no means a fixed and indifferent thing. The study of any growing plant in reference to this one relation presents a multitude of problems to those who know how to observe. B. On horizontal stems. 23. Examples of horizontal stems, that is. stems exposed on one side to the direct light, will be found in the ease of many branches of trees, stems prostrate on the ground, and FOLIAGE LEAVES: THE LIGHT-RELATION. 23 stems against a support, as the ivies. It is only necessary to notice how the leaves are adjusted to hght on an erect stem, und then to bend the stem into a horizontal posi- tion or against a support, to realize how unfavorable the sume arrangement would be. and how many new ad- justments must be made. The leaf blades must all be brought to the light side of the stem, so far as possible, and those that belong to the lower side of the stem must be fitted imto the spaces left by the leaves which belong to the upper This may be brought about by the twisting of the stem, the twisting of the petioles. the bending of the blade on the petiole, the lengthening of petioles, or in some other way. Every horizontal stem has its own special problems of leaf adjustment which may be observed (see Figs. 18, 50). Sometimes there is not space enough for the full development of every blade, and smaller ones are fitted side. into the spaces left by the larger ones (see Fig. 21). Fig. 17. lobed leaves, the rising of the petioles to adjust the blades to light, and the general cylindrical habit. A chrysanthemum, showing This sometimes resultsin what are called unequally paired leaves, where opposite leayes develop one large blade and one small 24 PLANT RELATIONS. one. Perhaps the most complete fitting together of leaves is found in certain ivies, where a regular layer of angular interlocking leaves is formed, the leaves fitting together like rm SB TRL REL EE a ome anaes ESET) Fie. 18. A plant (Pellionia) with drooping stems, showing how the leaves are all brought to the lighted side and fitted together. the pieces of a mosaic. In fact such an arrangement is known as the mosaic arrangement, and involves such an amount of twisting, displacement, elongation of petioles, “SUIPLYS Ploav 07 OYIASO) payy are Lay] MOY SULMOYS ‘saaval BIUOseg Jo orvsoUl Y “EL “OL 26 PLANT RELATIONS. Fre. 20. A spray of maple, showing the adjustment of the leaves in size and position of blades and length of petioles to secure exposure to light on « horizontal stem.— After KEnNER. etc., as to give ample evidence of the effort put forth by plants to secure a favorable light-relation for their foliage = SSS ‘ ~ = = Fig. 21. Two plants showing adjustment of Jeaves on a horizontal stem. The plant to the left is nightshade, in which small blades are fitted into spaces left by the large ones. The plant to the right ix Sclaginella, in which small leaves are dis- tributed along the sides of the stem, and oticrs are displayed along the upper sur- face.—After Kerner. FOLIAGE LEAVES: THE LIGHT-RELATION. OW. leaves (see Figs. 19, 22). In the case of ordinary shade trees every direction of branch may be found, and the resulting adjustment of leaves noted (see Fig. 20). Looking up into a tree in full foliage, it will be noticed that the horizontal branches are comparatively bare be- Fic. 22. A mosaic of fern (Adiantum) leaflets. neath, while the leaf blades have been carried to the upper side and have assumed a mosaic arrangement. Sprays of maidenhair fern (see Fig. 22) show a remark- able amount of adjustment of the leaflets to the light side. Another group of fern-plants, known as club-mosses, has horizontal stems clothed with numerous very small leaves. These leaves may he seen taking advantage of all the space on the lighted side (see Fig. 21). CHAPTER III. FOLIAGE LEAVES: FUNCTION, STRUCTURE, AND PROTEO- TION. A. Functions of foliage leaves. 24, Functions in general We have observed that foliage leaves are light-related organs, and that this relation is an important one is evident from the various kinds of adjust- ment used to secure it. We infer, therefore, that for some important function of these leaves light is necessary. It would be hasty to suppose that light is necessary for every kind of work done by a foliage leaf, for some forms of work might be carried on by the leaf that light neither helps nor hinders. Foliage leaves are not confined to one function, but are concerned in « variety of processes, all of which have to do with the great work of nutrition. Among the variety of functions which belong to foliage leaves some of the most important may he selected for mention. It will be possible to do little more than indicate these functions until the plant with all its organs is considered, but some evidence can be obtained that various processes are taking place in the foliage leaf. 25. Photosynthesis—The most important function of the foliage leaf may be detected by a simple experiment. If an active leaf or a water plant be submerged in water ina glass vessel, and exposed to the hght, bubbles may be seen coming from the leaf surface and rising through the water (see Fig. 23). The water is merely a device by which the bubbles of gas may be seen. If the leaf is very active the FOLIAGE LEAVES: FUNCTION, STRUCTURE, ETC. 29 bubbles are numerous. That this activity holds a definite relation to light may be proved by gradually removing the vessel containing the leaf from the light. As the light diminishes the bubbles diminish in number, and when a Fig. 23. An experiment to illustrate the giving off of oxygen in the process of photo. synthesis. certain amount of darkness has been reached the bubbles will cease entirely. If now the vessel be brought back gradually into the light. the bubbles will reappear, more and more numerous as the light increases. That this gas being given off is oxygen may be proved by collecting the 30 PLANT RELATIONS. bubbles in a test tube, as in an ordinary chemical experi- ment for collecting gas over water, and testing it in the usual way. Some very important things are learned by this experi- ment. It is evident that some process is going on within the leaf which needs light and which results in giving off oxygen. It is further evident that as oxygen is eliminated, the process indicated is dealing with substances which contain more oxygen than is needed. The amount of oxygen given off may be taken as the measure of the work. The more oxygen, the more work; and, as we have observed, the more light, the more oxygen; and no light, no oxygen. Therefore, light must be essential to the work of which the elimination of oxygen is an external indication. That this process, whatever it may be, is so essentially related to light, suggests the idea that it is the special process which demands that the leaf shall be a light-related organ. If so, it isa dominating kind of work, as it chiefly determines the life-relations of foliage leaves. The process thus indicated is known as photosynthesis, and the name suggests that it has to do with the arrange- ment of material with the help of hght. It is really a pro- cess of food manufacture, by which raw materials are made into plant food. This process is an exceedingly important one, for upon it depend the lives of all plants and animals. The foliage leaves may be considered, therefore, as spectul organs of photosynthesis. They are special organs, not ex- clusive organs, forany green tissue, whether on stem or fruit or any part of the plant body, may do the same work. It is at once apparent, also, that during the night the process of photosynthesis is not going on, wnd therefore during the night oxygen is not being given off. Another part of this process is not so easily observed, but is so closely related to the elimination of oxygen that it must be mentioned. Carbon dioxide occurs in the air to which the foliage leaves are exposed. It is given off from FOLIAGE LEAVES: FUNCTION, STRUCTURE, ETC. 81 our lungs in breathing, and also comes off from burning wood or coal. It is a common waste product, being a com- bination of carbon and oxygen so intimate that the two elements are separated from one another with great dif- ficulty. During the process of photosynthesis it has been discovered that carbon dioxide is being absorbed from the air by the leaves. As this gas is absorbed chiefly by green parts and in the light, in just the conditions in which oxy- gen is being given off, it is natural to connect the two, and to infer that the process of photosynthesis involves not only the green color and the light, but also the absorption of carbon dioxide and the elimination of oxygen. When we observe that carbon dioxide is a combination of carbon and oxygen, it seems reasonable to suppose that the carbon and oxygen are separated from one another in the plant, and that the carbon is retained and the oxygen given back to the air. The process of photosynthesis may be partially defined, therefore, as the breaking up of carbon dioxide by the green parts of the plants in the presence of light, the retention of the carbon, and the elimination of the oxygen. The carbon retained is combined into real plant food, in a way to be described later. We may con- sider photosynthesis as the most important function of the foliage leaf, of which the absorption of carbon dioxide and the evolution of oxygen are external indications ; and that light and chlorophyll are in some way essentially connected with it. 26, Transpiration.—One of the easiest things to observe in connection with a working leaf is the fact that it gives off moisture. A simple experiment may demonstrate this. If a glass vessel (bell jar) be inverted over a small active plant the moisture is seen to condense on the glass, and even to trickle down the sides. A still more convenient way to demonstrate this is to select a single vigorous leaf with a good petiole ; pass the petiole through a perforated card- board resting upon a tumbler containing water, and invert 32 PLANT RELATIONS. a second tumbler over the blade of the leaf, which projects above the cardboard (see Fig. 24). It will be observed that moisture given off from the surface of the working leaf is condensed on the inner surface of the inverted tumbler. The cardboard is to shut off evaporation from the water in the lower tumbler. When the amount of water given off by a single leaf is noted, some vague idea may be formed as to the amount ot moisture given off by a great mass of vegetation, such as a meadow or a forest. It is evident that green plants at work are contributing a very large amount of moisture to the air in the form of water vapor, moisture which has been absorbed by some region of the plant. The foliage leaf, therefore, may be regarded as an organ of transpiration, not that the leaves alone are engaged in transpiration, for many parts of the plant do the same thing, but because the foliage leaves are the chief seat of transpiration. The important fact in connection with transpiration is not that moisture is given off by active foliage leaves, but that this escaping moisture is the external indication of some work going on within the leaf. Transpiration, therefore, may not be regarded so much as work, as the result, and hence the indication of work. In case the leaves are submerged, as is true of many plants, it is evi- dent that transpiration is practically checked, for the leaves are already bathed with water, and under such cir- cumstances water vapor is not given off. The same is true of green water plants without leaves (such as alge). It is evident that under such circumstances leaf work must be carried on without transpiration. 2. Respiration ——.\nother kind of work also may be de- tected in the foliage leaf, but not so easily described. In fact it escaped the attention of hotanists long after they had discovered photosynthesis and transpiration. Itis work that goes on so long as the leaf is alive, never ceasing day ornight. The external indication of it is the absorption Fra. 24. Experiment illustrating transpiration. 34 PLANT RELATIONS. of oxygen and the giving out of carbon dioxide. It will be noted at once that this is exactly the reverse of what takes place in photosynthesis. During the day, therefore, carbon dioxide and oxygen are both being absorbed and evolved. It will also be noted that the taking in of oxygen and the giving out of carbon dioxide is just the sort of exchange which takes place in our own respiration. In fact this pro- cess is also called respiration in plants. It does not depend upon light, for it goes on in the dark. It does not depend apon chlorophyll, for it goes on in plants and parts of plants which are not green. It is not peculiar to leaves, but goes on in every living part of the plant. A process which goes on without interruption in all living plants and animals must be very closely related to their living. We conclude, therefore, that while photosynthesis is peculiar to green plants, and only takes place in them when light is present, respiration is necessary to all plants in all conditions, and that when it ceases life must soon cease. The fact is, respiration supplies the energy which enables the living substance to work. Once it was thought that plants differ from animals in the fact that plants absorb carbon dioxide and give off oxygen, while animals absorb oxygen and give off carbon dioxide. Tt is seen now that there is no such difference, but that respiration (absorption of oxygen and evolution of carbon dioxide) is common to both plants and animals. The difference is that green plants have the added work of photosynthesis. We may also call the foliage leaf, therefore, an organ of respiration, because so much of such work is done hy it, but it must be remembered that respiration is going on in every living part of the plant. This by no means completes the list of functions that might he made out for foliage leaves, but it serves to indicate both their peculiar work (photosynthesis) and the fact that they are doing other kinds of work as well. FOLIAGE LEAVES: FUNCTION, STRUCTURE, ETC. 85 B. Structure of foliage leaves. 28. Gross structure.—It is evident that the essential part of a foliage leaf is its expanded portion or blade. Often the leaf is all blade (sce Figs. 7, 8, 18) ; frequently there is a longer or shorter leaf-stalk (petiolv) which helps to put Pile fs Mh iG eathpcrta: ne V eS ee Ten ae, = See l ! cn Fie. 25. Two types of leaf venation. The figure to the left is a leaf of Solomon’s seal (Polygonatum), and shows the principal veins parallel, the very minute cross veinlets being invisible to the naked cye, being a monocotyl type. The figure to the right is a leaf of a willow, and shows netted veins, the main central vein (mid- rib) sending out a series of parallel branches, which are connected with one another by a network of veinlets, being a dicotyl type.—After ErrInGsHAUSEN. the blade into better light-relation (see Figs. 1, 9,17, 20, 26); and sometimes there are little leaf-like appendayes (stip- ules) on the petiole where it joins the stem, whose fune- tion is not always clear. Upon examining the blade it is seen to consist of a green substance through which a 86 PLANT RELATIONS, framework of veins is variously arranged. The large veins which enter the blade send off smaller branches, and these send off still smaller ones, until the smallest veinlets are Fic. 26. A leaf of hawthorn, showing a short petiole, and a broad toothed blade with a conspicuous network of veins. Note the relation between the veins and the tecth.— After SrRASBURGER. invisible, and the framework is a close network of branching veins. This is plainly shown bya ‘‘skel- eton” leaf, one which has been so treated that all the green sub- stance has disap- peared, and only the network of veinsremains. It will be noticed that in some leaves the veins and yveinlets are very prominent, in others only the main veins are prominent, while in some it is hard to detect any veins (see Figs. 25, 26). 20. Significance of leaf veins,—It is clear that the framework of veins is doing at least two things for the blade: (1) it mechanically supports the spread out green sub- stance ; and (2) if conducts material to and from the green substance. So complete is the network of veins that this FOLIAGE LEAVES: FUNCTION, STRUCTURE, ETC. 37 support and conduction are very perfect (see Fig. 27). It is also clear that the green substance thus supported and supplicd with material is the important part of the leaf, the part that demands the light-relation, Study the various plans of the vein systems in Figs. 3, 9, 13, 18, 19, 20, 21, 20, 20, d1, 70, 76, 52, 83, 92, 161. e ne BS EAS Maas a a Ve Fie. 27. A plant (Fittonia) whose leaves show a network of veins, and also an adjust- ment to one another to form a mosaic. 30, Epidermis.—If a thick leaf be taken, such as that of a hyacinth, it will be found possible to peel off from its surface a delicate transparent skin (epidermis). This epidermis completely covers the leaf, and generally shows no green color. It is a protective covering, but at the same time it must not completely shut off the green substance beneath from the outside. It is found, therefore, that three important parts of an ordinary foliage leaf are: (1) 88 PLANT RELATIONS. a network of veins; (2) a green substance (mesophyll) in the meshes of the network ; and (3) over all an epidermis. 31. Stomata.—If a compound microscope is used, some very important additional facts may be discovered. The thin, transparent epidermis is found to be made up of a layer of cells which fit closely together, sometimes dovetailing with each other. Curious openings in the epidermis will also be discovered, sometimes in very great numbers. Guarding each opening are two crescent-shaped cells, known as fii Ba ik oP eats guard-cells, and between them a of Meranta, showing the Slit-like opening leads through the interlocking walls, and a enidermis. The whole apparatus stoma (s) with its two guard- , cells. is known as a stoma (plural stomata), Which really means “mouth,” of which the guard-cells might he called the lips (see Figs. 28, 29). Sometimes stomata are found only on the under side of the leaf, sometimes only on the upper side, and sometimes on both sides. The important fact about stomata is that the guard-cclls can change their shape, and so regulate the size of the opening. Itis not certain just how the guard-cells change their shape and just what stomata do for leaves. They are often called ‘ breathing pores,” but the name is very inappropriate. Stomata Fi. 29 A single : : ‘ stoma from the are not peculiar to the epidermis of foliage epidermis of a leaves, for they are found in the cpidermis lily leaf, show- of any green part, as stems, young fruit, ae on ete. It is evident, therefore, that they hold of chlorophyl, an important relation to green tissue which ene is covered by epidermis. Also, if we examine between, FOLIAGE LEAVES: FUNCTION, STRUCTURE, ETC. 39 foliage leaves and other green parts of plants which live submerged in water, we find that the epidermis contains no stomata. Therefore, stomata hold a definite relation to green parts covered by epidermis only when this epider- mis is exposed to the air. It would seem that the stomata supply open passage- ways for material from the green tissue through the epider- mis to the air, vr from the air to the green tissue, or both. It will be remembered. however, that quite a number of substances are taken into the leaf and given out from it, so that it is hard to determine whether the stomata are specially for any one of these movements. For instance, the leaf gives out moisture in transpiration, oxygen in photosynthesis, and carbon dioxide in respiration ; while it takes in carbon dioxide in photosynthesis, and oxygen in respiration. It is thought stomata specially favor transpira- tion, and, if so, ‘‘ breathing pores” is not a happy phrase, for they certainly assist in the other exchanges. 32. Mesophyll—If a cross-section be made of an ordi- nary foliage leaf, such as that of a lily, the three leaf regions can be secn in their proper relation to cach other. Bounding the section above and below is the layer of trans- parent epidermal cells. pierced here and there by stomata, marked by their peculiar guard-cells. Between the epi- dermal layers is the green tissue, known as the mesophyll. made up of cells which contain numerous small green bodies which give color to the whole leaf, and are known as chlorophyll bodies ov chloroplasts. The mesophyll cells are usually arranged differently in the upper and lower regions of the leaf. In the upper region the cells are elongated and stand upright, present- ing their narrow ends to the upper leaf surface. forming the palisade tissue. In the lower region the cells are irreg- ular, and so loosely arranged as to leave passageways for air between, forming the spongy tissue. The air spaces among the cells communicate with one another, so that a system of 4 40 PLANT RELATIONS. air chambers extends throughout the spongy mesophyll. It is into this system of air chambers that the stomata open, and so they are put into direct communication with the mesophyll or working cells. The peculiar arrangement of the upper mesophyll, to form the palisade tissue, has to do with the fact that that surface of the leaf is exposed to the direct rays of light. This light, so necessary to the mesophyll, is also dangerous for at least two reasons. If J st Fig. 30. A section through the leaf of lily, showing upper epidermis (we), lower cpi- dermis (Ze) with its stomata (sé), mesophyll (dotted cells) composed of the palisade region (p) and the spongy region (sp) with air spaces among the cells, and two veins (v) cut across. the light is too intense it may destroy the chlorophyll, and the heat may dry out the cells. By presenting only nar- row ends to this direct light the cells are less exposed to intense light and heat. Study Fig. 30. 33. Veins.—In the cross-section of the leaf there will also be seen here and there, embedded in the mesophyll, the cut ends of the veinlets, made up partly of thick- walled cells, which hold the leaf in shape and conduct material to and from the mesophyll (see Fig. 30). FOLIAGE LEAVES: FUNCTION, STRUCTURE, ETC. 41 C. Leuf protection. 34. Need of protection.—Such an important organ as the leaf, with its delicate active cells well displayed, is ex- posed to numerous dangers. Chief among these dangers are intense light, drought, and cold. ATI leaves are not exposed to these dangers. For example, plants which grow in the shade are not in danger from intense light ; many rater plants are not in danger from drought ; and plants of the tropical lowlands are in no “Zs. Fig. 31. Sections through leaves of the same plant, showing the effect of exposure to light upon the structure of the mesophyll. In both cases os indicates upper surface, and ws under surface. In the section at the left the growing leaf was exposed to direct and intense sunlight, and, as a consequence, all of the mesophyll cells have assumed the protected or palisade position. In the section at the right the leaf was grown in the shade, and none of the mesophyll cells have organized in palisade fashion.—After STAHL. danger from cold. The danger from all these sources is be- cause of the large surface with no great thickness of body, and the protection against all of them is practically the same. Most of the forms of protection can be reduced to two general plans: (1) the development of protective structures between the endangered mesophyll and the air ; (2) the diminution of the exposed surface. 35. Protective structures—The palisade arrangement of mesophyll may be regarded as an adaptation for protection, 42 PLANT RELATIONS. but it usually occurs, and does not necessarily imply ex- treme conditions of any kind. However, if the cells of the palisade tissue are unusually narrow and elongated, or C_ QW yyy : Ea eit Fie. 82. Section through a portion of the leaf of the yew (7axus), showing cuticle (c), epidermis (e), and the upper portion of the palisade cells (). form two or three layers, we might infer the probability of exposure to intense light or drought. The accompanying illustration (Fig. 31) shows in a striking way the effect of light intensity upon the structure of the mesophyll, by contrasting leaves of the same plant exposed to the extreme conditions of ight and shade. The most usual structural adaptations, however, are connected with the epidermis. The outer walls of the epi- dermal cells may become thickened, sometimes excessively so; the other epidermal walls may wlso become more or less thickened; or even what seems to be more than one epi- dermal laver is found protecting the meso- phyll. If the outer Fig. 338. Section through a portion of the leaf of walls of the epidermal carnation, showing the heavy cuticle (ew) HELLS ti formed by the outer walls of the epidermal eclis continue to eclls (ey). Through the cuticle a pussageway thicken, the outer re- leads to the stoma, whose two guard-cells are fs ne secu lying between the two epidermal cells S/on of the thick wall shown in the figure. Below the epidermal loses its structure cells some of the palisade cells (pad) are shown i ie containing chloroplasts, and below the stoma and forms the cuticle, is seen the air chamber into which it opens. which is one of the FOLIAGE LEAVES: FUNCTION, STRUCTURE, ETC. 48 Fie, 34. A hair from the leaf of Potentilla. It is seen to grow out from the epi- dermis, best protective substances (see Fig. 32). Sometimes this cuticle be- comes so thick that the passage- ways through it leading down to the stomata become regular canals (see Fig. 33), Another very common protective structure upon leaves is to be found in the great variety of hairs de- veloped by the epidermis. These may form but «a slightly downy covering, or the leaf may be cov- ered by a woolly or felt-like mass so that the epidermis is entirely concealed. The common mullein is a good illustration of a felt- covered leaf (see Fig. 36), In cold or dry regions the hairy covering of leaves is very noticeable, often giving them a brillant silky white or bronze look (see Figs. 34, 35). Sometimes, instead of a hair-like cover- ing, the epidermis develops scales of various patterns, often overlapping, and forming an excellent protection (see Fig. 37). In all these cases it should be remembered that these hairs and scales may serve other purposes also, as well as that of protection. 36, Diminution of exposed surface.— It will be impossible to give more than a few illustrations of this large subject. In very dry regions it has always been noticed that the leaves are small and Fie. 35. A section through the leaf of bush clover (Lespedeza), showing upper and lower epidermis, palisade cells, and cells of the spongy region. The lower epidermis produces numerous hairs which bend sharply and lie along the leaf surface (appressed), forming a close covering. 44 PLANT RELATIONS. Fig. 36. A branching hair from the leaf of common mullein. The whole plant has a felt-like covering composed of such hairs. comparatively thick, although they may be very numerous (see Figs. 4, 167). In this way each leaf exposes a small Fie. 37. A scale from the leaf of Shepherdia. These scales overlap and form a complete covering. surface to the dry- ing air and intense sunlight. In our southwestern dry regions the cactus abounds, plants which have reduced their leaves so much that they are no longer used for chlorophyll work, and are not usually recognized as leaves. In their stead the globular or eylin- drical or flattened stems are green and do leaf work (Figs, ‘svoond aes aq 07 adv 4] JO apIS Jay}LO UO pue “qand jrasop PEALo[-[[BUIS B ST SOSNJOVI IBMUIN[OS OA} YI WAEMJO|T “sNyORO vad ATYoLd B SL PuNOASYorgy atuonysa ay} ul puv { saioy snjovo [worrayds [[wUUs 918 puNOIS ayy UO Yo, puL IY oy) ye $ sutZOy sMyovo TVUUL[OD BIB 1]U9d 9Y} NT “SaAveT Yoryy {79a YALA “SOAUSE aTU JJo[ PUB ISH omayxX9 oy} YY ‘oovysns Jeol poonpas Surmoys “s}lasap suyjouo ay} MOI syuuld Jo dnowS y “ge ‘Ola Fic. 39. A group of cactus forms (slender cylindrical, columnar, and globular), all of them spiny and without leaves ; an agave in front ; clusters of yucca flowers in the background. FOLIAGE LEAVES: FUNCTION, STRUCTURE, ETC. 47 38, 89, 40, 185, 186, 187, 188). In the same regions the agaves and yuccas retain their leaves, but they become so thick that they serve as water reservoirs (see Figs. 38, 39, “A Fig. 40. A globular cactus, showing the ribbed stem, the strong spines, and the entire absence of leaves. 189). In all these cases this reduced surface is supple- mented by palisade tissue, very thick epidermal walls, and an abundant cuticle. 37. Rosette arrangement.—The rosette arrangement of leaves is a very common method of protection used by 48 PLANT RELATIONS. small plants growing in exposed situations, as bare rocks and sandy ground. ‘he cluster of leaves, flat upon the ground, or nearly so, and more or less overlapping, is very effectively arranged for resisting intense light or drought or cold (see Figs. 11, 12, 4s). 3x. Protective positions—In other cases, a position is assumed by the leaves which directs their flat surfaces so that they are not exposed to the most intense rays of light. The so-called “‘ com- Fie. 41. A leaf of a sensitive plant in two conditions. In the figure to the left the leaf is fully expanded, with its four main divisions and numerous leaflets well spread. In the figure to the right is shown the same leaf aftcr it has been “‘shocked”? by » sndden touch, or by sudden heat, or in some other way. The leaflets have been thrown together forward aud upward ; the four main divisions have been moved together; and the main leaf-stalk has been directed sharply downward. The whole change has very much reduced the surface of exposure.— After DUCHARTRE. pass plants,’ already mentioned, are illustrations of this, the leaves standing edgewise and receiving on their surface the less intense rays of light (see Figs. 5, 165). In the dry regions of Australia the leaves on many of the forest trees and shrubs have this characteristic edgewise position, known as the profile posilion, giving to the foliage a very curious appearance. Some leaves have the power of shifting their position according to their necds, directing their flat surfaces to- ward the light, or more or less inchning them, according Fie. 42. The telegraph plant (Desmodium gyrans). Each leaf is made up of three leaflets, a large terminal one, and a pair of small lateral ones. In the lowest figure the large leaflets are spread out in their day position ; in the central figure they are turned sharply downward in their night position. The name of the plant refers to the peculiar and constant motion of the pair of lateral leaflets, each one of which describes a curve with u jerking motion, like the second-hand of a watch, as indicated in the uppermost figure. 50 PLANT RELATIONS. to the danger. Perhaps the most completely adapted leaves of this kind are those of the ‘‘sensitive plants,” whose leaves respond to various external influences by changing their positions. The common sensitive plant abounds in dry regions, and may be taken as a type of such plants (see Figs. 4, £1, 156). The leaves are divided into very numerous small leaflets, sometimes very small, which stretch in pairs along the leaf branches. When drought approaches, some of the pairs of leaflets fold to- gether, slightly reduc- ing the surface expo- sure. As the drought continues, more leaflets fold together, then still others, until finally all the leaflets may be folded together, and the leaves themselves may Fie. 43. Colyledons of squash seedling, show- bend. aginst the stem. diskness Gight Ngure)—Atter Atkinson. It is like a sailing vessel gradually tuking in sail as a storm approaches, until finally nothing is exposed, and the vessel weathers the storm by presenting only bare poles. Sensitive plants can thus regulate the exposed sur- face very exactly to the need. Such motile leaves not only behave in this manner at the coming of drought, but the positions of the leaflets are shifted throughout the day in reference to light, and at night a very characteristic position is axsumed (sce Pigs. 2, 3, 42), once called a “sleeping position.” The danger from night exposure comes from the radiation of heat which oceurs, which may chill the leaves to the danger point. The night position of the leaflets of Ovel/x hag heen re- ferred to already (see $14). Similar changes in the direc- tion of the leaf planes at the coming of night may be observed in most of the Leyuminose, even the common FOLIAGE LEAVES: FUNCTION, STRUCTURE, ETC. 51 white clover displaying it. It can be observed that the expanded seed leaves (codyledons) of many young germinat- ing plants shift their positions at night (see Fig. 43), often assuming a vertical position which brings them in contact with one another, and also covers the stem bud (pluie). Certain leaves with well-developed protective structures are able to en- dure the winter, as in the case of the so-called evergreens. In the case of juniper, however, the winter and summer positions of the leaves are quite different (sce Fig. 44). In the winter the leaves le close against the stem and overlap one another; while with the coming of warmer conditions they become widely spreading. 39. Protection against rain.—It is also necessary for leaves to avoid Fis. 4 Two twiss of junt- = per, showing the effect of becoming wet by rain. If the water heat and cold upon the is allowed to soak in there is danger positions of the lcaves. ree 7 = The ordinary protected of filling the stomata and interfering qintee qiosition “of the with the air exchanges. Hence it leaves is shown by 4; hi ] Sewel that ay eaed aie while in B, in response to will be noticed that most leaves are varmer iconditious) the able to shed water, partly by their leaves have spread apart and have become freely ex- positions, partly by their structure. eae Ate h Gener: In many plants the leaves are so ar- ranged that the water runs off towards the stem and so reaches the main root system: in other plants the rain is shed outwards, as from the eaves of a house. Some of the structures which prevent the rain from soaking in are a smooth epidermis, a cuticle layer, waxy secretions. felt-like coverings, etc. Interesting experi- ments may be performed with different leaves to test their power of shedding water. If a gentle spray of water is allowed to play upon different plants, it will be observed 52 PLANT RELATIONS. that the water glances off at once from the surfaces of some leaves, runs off more slowly from others, and may be more or less retained by others. In this same connection it should be noticed that in most horizontal leaves the two surfaces differ more or less in appearance, the upper usually being smoother than the lower, and the stomata occurring in larger numbers, some- times exclusively, upon the under surface. While these differences doubtless have a more important meaning than protection against wetting, they are also suggestive in this connection. CHAPTER IV. SHOOTS. 40. General characters.—The term shoot is used to include both stem and leaves. Among the lower plants, such as the alge and toadstools, there is no distinct stem and leaf. In such plants the working body is spoken of as the thallus, which does the work done by both stem and leaf in the higher plants. These two kinds of work are separated in the higher plants, and the shoot is differentiated into stem and leaves. 41. Life-relation—In seeking to discover the essential life-relation of the stem, it is evident that it is not neces- sarily a light-relation, as in the case of the foliage leaf, for many stems are subterranean. Also, in general, the stem is not an expanded organ, as is the ordinary foli- age leaf. his indicates that whatever may be its essential life-relation it has little to do with exposure of surface. It becomes plain that the stem is the great leaf-hearing organ, and that its life-relation is a leaf-relation. Often stems branch, and this increases their power of producing leaves. In classifying stems, therefore, it seems natural to use the kind of leaves they bear. From this standpoint there are three prominent kinds of stems: (1) those bearing foli- age leaves ; (2) those bearing scaly leaves ; and (3) those bearing floral leaves. There are some peculiar forms of stems which do not bear leaves of any kind, but they need not be included in this general view. b4 PLANT RELATIONS. A. Stems bearing foliage leaves. 42. General character.—.\s the purpose of this stem is to display foliage leaves, and as it has been discovered that the essential life-relation of foliage leaves is the light-relation, it follows that a stem of this type must be able to relate its leaves to light. Itis, therefore, commonly aerial, and that it may properly display the leaves it is generally elongated, with its joints (xodes) bearing the leaves well separated (see Figs. 1, 4, 18, 20). The foliage-bearing stem is generally the most conspicu- ous part of the plant and gives style to the whole body. Qne’s impression of the forms of most plants is obtained from the foliage-bearing stems. Such stems have great range in size and length of life, from minute size and very short life to’ huge trees which may endure for centuries. Branching is also quite a feature of foliage-bearing stems ; and when it occurs it is evident that the power of displiy- ing foliave is correspondingly increased. Certain promi- nent types of foliage-bearing stems may be considered. +5. The subterranean type.—It may seem strange to in- clude any subterranean stem with those that bear foliage, as such a stem seems to be away from any light-relation. Ordinarily subterranean stems send foliage-bearing branches above the surface, and such stems are not to be classed as foliage-bearing stems. But often the only stem possessed by the plant is subterranean, and no branches are sent to the surface. In such cases only foliage leaves appear above ground, and they come directly from the subterranean stem. The ordinary ferns furnish a conspicuous illustration of this habit, all that is seen of them above ground being the characteristic leaves, the commonly called ++ stem” being only the petiole of the leaf (see Figs. 45, £6, 144). Many seed plants can also be found which show the same habit, especially those which flower early in the spring. This cannot be regarded as avery favorable type of stem for TES SDHFOS HAS AM oe SOS SO SSS = sspuoue . we $ 2% ow Fie. 45. A fern (Aspidium), showing three large branching leaves coming from a hori- zontal subterranean stem (rootstock) ; growing leaves are also shown, which are gradually unrolling. The stem, young leaves, and petioles of the large leaves are thickly covered with protecting hairs. The stem gives rise to numerous small roots from its lower surface. The figure marked 3 represents the under surface of a portion of the leaf, showing seven groups of spore cases; at 5 is represented a section through one of these groups, showing how the spore cases are attached and protected by a flap ; while at 6 is represented a single spore case opening and dis- charging its spores, the heavy spring-like ring extending along the back and over the top.—After WossIDLo, 5 d6 PLANT RELATIONS. leaf display, and as a rule such stems do not produce many foliage leaves, but the leaves are apt to be large. Fie. 46. A common fern, showing the underground stem (rootstock), which sends the few large foliage leaves above the surface.—After ATKINSON. The subterranean position is a good one, however, for purposes of protection against cold or drought, and when the foliage leaves are killed new ones can be put out by SHOOTS. 57 the protected stem. This position is also taken advantage of for comparatively safe food storage, and such stems are apt to become more or less thickened and distorted by this food deposit. 44. The procumbent type.—In this case the main body of the stem lies more or less prostrate, although the advanc- ing tip is usually erect. Such stems may spread in all directions, and become interwoven into a mat or carpet. They are found especially on sterile and exposed soil, G Fie. 47. A strawberry plant, showing a runner which has devel- oped a new plant, which in turn has sent out another run- ner.—After SEUBERT. and there may be an important relation between this fact and their habit, as there may not be sufficient building material for erect stems, and the erect position might result in too much exposure to light, or heat, or wind, etc. Whatever may be the cause of the procumbent habit, it has its advan- tages. As compared with the erect stem, there is economy of building material, for the rigid structures to enable it to stand upright are not necessary. On the other hand, such a stem loses in its power to display leaves. Instead of being free to put out its leaves in every direction, one side is against the ground, and the space for leaves is diminished at least one-half. All the leaves it bears are necessarily directed towards the free side (see Fig. 18). We may be sure, however, that any disadvantage com- ing from this unfavorable position for leaf display is over- balanced by advantages in other respects. The position is 58 PLANT RELATIONS. certainly one of protection, and it has a further advantage in the way of migration and vegetative propagation. As the stem advances over the ground, roots strike out of the nodes into the soil. In this way fresh anchorage and new soil supplies are secured ; the old parts of the stem may Fie. 48. Two plants of a saxifrage, showing rosette habit, and also the numerous runners sent out from the base, which strike root at tip and produce new plants. —After Kerner. ie, but the newer portions have their soil connection and continue to live. So effective is this habit for this kind of propagation that plants with erect stems often make use of it, sending out from near the base special prostrate branches, which advance over the ground and form new plants. A very familiar illustration is furnished by the straw- berry plant, which sends out peculiar naked ‘ runners” to strike root and form new plants, which then become SHOOTS. 59 independent plants by the dying of the runners (see Figs. ae, 45. The floating type.—In this case the stems are sus- tained by water. Numerous illustrations can be found in small inland lakes and slow-moving streams (see Fig. 41). Beneath the water these stems often seem quite erect, but Fie, 49. A submerged plant (Ceratophyllum) with floating stems, showing the stem joints bearing finely divided leaves. when taken out they collapse, lacking the buoyant power of the water. (irowing free and more or less upright in the water, they seem to have all the freedom of erect stems in displaying foliage leaves, and at the same time they are not called upon to build rigid structures. Economy of building material and entire freedom to display foliage would seem to be a happy combination for plants. It must be noticed, however, that another very important condition is introduced. To reach the leaf surfaces the light must pass through the water, and this diminishes its intensity so 60 PLANT RELATIONS. greatly that the working power of the leaves is reduced. At no very great depth of water a limit is reached, beyond which the light is no longer able to be of service to the leaves in their work. Hence it is that water plants are Fig. 50. A vine or liana climbing the trunk of a tree. The leaves are all adjusted to face the light and to ayoid shading one an- other as far as possible, restricted to the surface of the water, or to shoal places ; and in such places vegetation is very abundant. Water is so serious an impediment to light that very many plants bring their working leaves to the surface and float them, as seen in water lilies, thus obtaining light of undiminished intensity. 46. The climbing type.—Climb- ing stems are developed especially in the tropics, where the yvegeta- tion is so dense and overshadow- ing that many stems have learned to climb upon the bodies of other plants, and so spread their leaves in better light (see Figs. 50, 55, 98, 201). Great woody vines fairly interlace the vegetation of tropical forests, and are known as ‘‘lianas,” or ‘‘lianes.*” The same habit is noticeable, also, in our temperate vegetation, but it is by no means so extensively dis- played as in the tropics. There are a good many forms of climb- ing stems. Remembering that the habit refers to one stem de- pending upon another for mechanical support, we may in- clude many hedge plants in the SHOOTS. 61 list of climbers. In this case the stems are too weak to stand alone, but by interlacing with one another they may keep an upright position. There are stems, also, which climb by twining about their support, as the hop vine and Fie, 51. A cluster of smilax, showing the tendrils which enable it to climb, and also the pricklcs.—After KERNER. morning glory : others which put out tendrils to grasp the support (see Figs. 51, 52), as the grapevine and star cucumber ; and still others which climb by sending out suckers to act as holdfasts, as the woodbine (see Figs. 53, 54). In all these cases there is an attempt to reach towards 62 PLANT RELATIONS. the light without developing such structures in the stem as would enable it to stand upright. 47. The erect type—This type seems altogether the best adapted for the proper display of foliage leaves. Leaves Piece Eee a Fig. 52. Passion-flower vines climbing supports by means of tendrils, which may be seen more or less extended or coiled, The two types of leaves upon a single stem may also be noted. can be sent out in all directions and carried upward to- wards the light ; but it is at the expense of developing an elaborate mechanical system to enable the stem to retain this position, There is an interesting relation between these erect bodies and zones of temperature. At high alti- SHOOTS. Fie. 538. Woodbine (.4 mpelopsis) in a deciduous forest. The tree trunks are almost covered by the dense masses of woodbine, whose leaves are adjusted so as to form compact mosaics. A lower stratum of vegetation is visible, composed of shrubs and tall herbs, showing that the forest is somewhat open.—After SCHIMPER. tudes or latitudes the subter- ranean and prostrate types of foliage-bearing stems are most common ; and as one passes to lower altitudes or latitudes the erect stems become more nu- merous and more lofty. Among stems of the erect type the tree is the most impressive, and it has developed into a great vari- ety of forms or ‘‘ habits.” Any one recognizes the great differ- ence in the habits of the pine and the elm (see [igs. 56, 57, 48, 59), and many of our Fic. 54. A portion of a woodbine (Ampelopsis). The stem tendrils have attached themselves to a smooth wall by means of disk-like suckers.—After STRASBURGER. “AHANIHOY 19}J} Y¥—'SOUlA 9} JO S}IqVY SUIAIVA 9Y} BION *}8aI0J pvordow v UI svUBI[ Jo Av[dsIP Y “Sg ‘Ol, eT * << Tao an = * eS Fie. 56. A tree of the pine type (larch), showing the continuous central shaft and the horizontal branches, which tend to become more upright towards the top of the tree. The general outline is distinctly conical. such trees in periodically shedding its leaves. The larch is peculiar among Fie. 57. A pine tree, showing the central shaft and also the bunching of the needle leaves toward the tips of the branches where there is the best exposure to light. SHOOTS. 67 common trees may be known, even at a distance, by their characteristic habits (see Figs. 60, 61, 62). The difficulty of the mechanical problems solved by these huge bodies is very great. They maintain form and position and en- dure tremendous pressure and strain. Fie. 58. An elm in its winter condition, showing the absence of a continuous central shaft, the main stem soon breaking up into branches, and giving a spreading top. On each side in the background are trees of the pine type, showing the central shaft and conical outline, 68 PLANT RELATIONS. 48, Relation to light.—As stems bearing foliage leaves hold a special relation to light, it is necessary to speak of the influence of light upon the direction of growth, an ah ee Fie. 59. An elm in foliage, showing the breaking up of the trunk into branches and the spreading top. influence known as heliotropism, already referred to under foliage leaves. In the case of an erect stem the tendency is to grow towards the source of light (see Figs. 1, 64). SHOOTS. 69 This has the general result of placing the leaf blades at right angles to the rays of light, and in this respect the heliotropism of the stem aids in securing a favorable leaf position (see Figs. 63, 63a). Prostrate stems are differently affected by the light, however, being directed transversely to the rays of light. The same is true of many foliage ne Fig. 60. An oak in its winter condition, showing the wide branching. The various directions of the branches have been determined by the light-relations. branches, as may be seen by observing almost any tree in which the lower branches are in the general transverse posi- tion. These branches generally tend to turn upwards when they are beyond the region of shading. Subterranean stems are also mostly horizontal, but they are out of the influence of light, and under the influence of gravity, known as geotropism, which guides them into the trans- verse position, The climbing stem, like the erect one, 70 PLANT RELATIONS. ee we OL SoU Fie. 61. Cottonwoods, in winter condition, on a sand dune, showing the branching habit, and the tendency to grow in groups. grows towards the light, while floating stems may be either erect or transverse. B. Stems bearing scale leuves. 49, General character.—.\ scale leaf is one which does not serve as foliage, as it does not develop the necessary chlorophyll. This means that it does not need such an exposure of surface, and hence scale leaves are usually much smaller, and certainly are more inconspicuous than foliage leaves. A good illustration of scale leaves is furnished hy the ordinary scaly buds of trees, in which the covering of overlapping scaly leaves is very conspicuous (see Fig. 65). As there is no development of chlorophyll in such leayes, SHOOTS. 71 they do not need to be exposed to the light. Stems bearing only scale leaves, therefore, hold no necessary light-relation, and may be subterranean as well as aerial. For the same Fie. 62. A group of weeping birches, showing the branching habit and the peculiar hanging branchlets. The trunks also show the habit of birch bark in peeling off in bands around the stem. reason scale leaves do not need to be separated from one another, but may overlap, as in the buds referred to. Sometimes scale leaves occur so intermixed with foliage 6 a “a Fia. 63. Sunflowers with the upper part of the stem sharply bent towards the light, giving the leaves better exposure.—After SCHAFFNER. SHOOTS. 73 leaves that no peculiar stem type is developed. In the pines scale leaves are found abundantly on the stems which are developed for foliage purposes. In fact, the main stem axes of pines bear only scale leaves, while short spur-like branches bear the characteristic needles, or foliage leaves, but the form of the stem is controlled by the needs of the foliage. Some very distinct types of scale-bearing stems may be noted. 50. The bud type. —TIn this case the nodes bearing the leaves remain close together, not sepa- rating, as is neces- sary in ordinary foliage-bearing stems, and the leaves overlap. In it a stem of this char- Fie. 63a. Cotyledons of castor-oil bean ; the seedling acter the later joints to the left showing the ordinary position of the may become s epa- cotyledons, the one to the right showing the curva- J . ture of the stem in response to light from one rated and bear foli- side.—After ATKINSON. age leaves, so that one finds scale leaves below and foliage leaves above on the same stem axis. This is always true in the case of branch buds, in which the scale leaves serve the purpose of protection, and are aerial, not because they need a light-relation, but because they are protecting young foli- age leaves which do. Sometimes the scale leaves of this bud type of stem do not serve so much for protection as for food storage, and become fleshy. Ordinary bulbs, such as those of lilies, etc., Fie. 64. An araucarian pine, showing the central shaft, and the regular clusters of branches spreading in every direction and bearing numerous small leaves. The low- ermost branches extend downwards and are the largest, while those above become more horizontal and smaller. These dif- ferences in the size and direction of the branches secure the largest light expo- sure, 74 PLANT RELATIONS. are of this character ; and as the main pur- pose is food storage the most favorable position is a subter- ranean one (see Fig. 66). Sometimes such scale leaves become very broad and not merely overlap but en- wrap one another, as in the case of the onion. 51. The tuber type. —The ordinary potato may be taken as an il- lustration (see Fig. 67). The minuie scale leaves. to be found at the ‘‘eyes” of the potato, do not overlap, which means that the stem joints are farther apart than in the bud type. The whole form of the stem results from its use as a place of food storage. and hence such stems are gencrally subterra- nean. Food storage, subterranean position, and reduced scale leaves are facts which seem to follow each other naturally. SHOOTS. 52. The rootstock type.—This is prob- ably the most common form of subter- ranean stem. It is elongated, as are foli- age stems, and hence the scale leaves are well separated. It is prominently used for food storage, and is also admirably adapted for subterranean migration (see Fig. 68). It can do for the plant, in the way of migration, what prostrate foliage- bearing stems do, and isinamore protected position. Advancing beneath the ground, it sends up a succession of branches to the surface. It is a very efficient method for the “‘spreading” of plants, and is extensively used by grasses in coy- ering areas and forming turf. The persist- ent continuance of the worst weeds is often due to this habit (see Figs. 69, 70). It is impossible to remove all of the indefinitely branching rootstocks from the soil, 75 Fie. 65. Branch buds of elm. Three buds (k) with their over- lapping scales are shown, each just above the scar (d) of an old leaf.— After BEHRENS. Fie. 66. A bulb, made up of overlap- ping scales, which are fleshy on account of food storage. — After Gray. and any fragments that remain are able to send up fresh crops of aerial branches. 53. Alternation of rest and activity.—In all of the three stem types just mentioned, it is important to note that they are associated with a remark- able alternation between rest and vigorous activity. From the branch buds the new leaves 76 Fie. 67. A potato plant, showing thesubterranean tubers.— After STRASBURGER. be covered suddenly with young vegetation. PLANT RELATIONS. emerge with great rapidity, and trees be- come covered with new foliage in a few days. From the sub- terranean stems the aerial parts come up so speedily that the surface of the ground seems to This sudden change from comparative rest to great activity has been well spoken of as the ‘“‘awakening ” of vegetation. C. Stems bearing floral leaves. 54. The flower.—The so-called “flowers” which certain plants produce represent another type of shoot, being stems with peculiar leaves. So attractive are flowers that they have been very much studied; and this fact has led many people to believe that flowers are the only parts of plants worth studying. Aside from the fact that a great many plants do not produce flowers, even in those that do the flowers are connected with only one of the plant pro- cesses, that of reproduction. Every one knows that flowers are exceedingly variable, and names Fig. 68. The rootstock of Solo- mon’s seal; from the under side roots arc developed ; and on the upper side are seen the scars which mark the positions of the successive aerial branches which bear the leaves. The advanc- ing tip is protected by scales (forming a bud), and the posi- tions of previous buds are in- dicated by groups of ring-like scars which mark the attach- ment of former scales. Advanc- ing in front and dying behind such a rootstock may give rise to an indefinite succession of acrial plants.—After Gray. SHOOTS. QT have been given to every kind of variation, so that their study is often not much more than learning the definitions of names. However, if we seek to discover the life-rela- tions of flowers we find that they may be stated very simply. 55. Life-relations—The flower is to produce seed. It must not only put itself into proper relation to do this, but Fic. 69. The rootstock of a rush (Juncus), showing how it advances beneath the ground and sends above the surface a succession of branches. The breaking up of such a rootstock only results in so many separate individuals.—After CowLes. there must also be some arrangement for putting the seeds into proper conditions for developing new plants. In the production of seed it is necessary for the flower to secure a transfer of certain yellowish, powdery bodies which it pro- duces, known as pollen or pollen-grains, to the organ in which the seeds are produced, known as the pisti/. This transfer is called pollination. One of the important things, therefore, in connection with the flower, is for it to put 18 PLANT RELATIONS. Fie. 70. An alpine willow, showing a strong rootstock developing aerial branches and roots, and capable of long life and extensive migration.—After SCHIMPER. itself into such relations that it may secure pollination. Fia. 71. A flower of peony, showing the four sets of floral organs: i, the sepals, together called the calyx ; c, the petals, together called the corolla ; wu, the numerous stamens; g, the two carpels, which contain the ovules.—After STRASBURGER. Besides pollination, which is necessary to the production of seeds, there must be an arrangement for seed distribution. It is always well for seeds to he scattered, so as to be separated from one another and from the parent plant. The two great external prob- lems in connection with the flower, therefore, are polli- SHOOTS. nation and seed-distribution. It is necessary to call attention to certain peculiar features of this type of stem. 56. Structures.—The joints of the stem do not spread apart, so that the peculiar leaves are kept close together, usually forming a rosette-like cluster (see Fig. 71). These leaves are of four kinds: the lowest (outermost) ones (indi- vidually sepals, collectively calyx) mostly resemble small foliage leaves ; the next higher (inner) set (individually petals, collectively corolla) are usually the most conspicuous, delicate in texture and brightly col- ored; the third set (stamens) produces the pollen; the highest (innermost) set (car- pels) form the pistil and pro- duce the ovules, which are to become seeds. These four sets may not all be present in the same flower; the members of the same set may be more or less blended with one another, forming tubes, urns, etc. (see Figs. 72, 78, 74); or the dif- ferent members may be modi- fied in the greatest variety of ways. Another peculiarity of this type of stem is that when the © 19 Fie.72. A group of flowers of the rose family. The one at the top (Poten- tilla) shows three broad sepals, much smaller petals alternating with them, a group of stamens, and a large receptacle bearing numer- oussmall carpels. The central one (Alchemilla) shows the tips of two small sepals, three larger petals united below, stamens arising from the rim of the urn, and.a single pe- culiar pistil. The lowest flower (the common apple) shows the sepals, petals, stamens, and three styles, all arising from the ovary part of the pistil.—After Focke. 80 PLANT RELATIONS. Fie, 73. 0—S—o—G==8 > o—S—o— G23 > 0—n, ete. In the case of heterosporous plants (some Pteridophytes and all Spermatophytes) it would be modified as follows : G_-0 > 0S $—§—8 > 0- SGT i=5 > 04K, ete. In this case two gametophytes are involved, one pro- ducing a sperm, the other an egg, which fuse and form the oospore, which in germination produces the sporophyte, which produces two kinds of asexual spores (megaspores and microspores), which in germination produce the two gametophytes again. One additional fact connected with heterospory should be mentioned, and that is the great reduction of the gam- etophyte. In the homosporous ferns the spore develops a small but free and independent prothallium which pro- duces both sex organs. When in heterosporous plants this work of producing sex organs is divided between two gam- etophytes they become very much reduced in size and lose their freedom and independence. They are so small that they do not escape entirely, if at all, from the embrace of the spores which produce them, and are mainly dependent for their nourishment upon the food stored up in the spores (Figs. 140, 141). As the spore is produced by the sporo- phyte, heterospory brings about a condition in which the gametophyte is dependent upon the sporophyte, an exact reversal of the condition in Bryophytes. The relative importance of the gametophyte and the sporophyte throughout the plant kingdom may be roughly indicated by the accompanying diagram, in which the c Ss shaded part of the parallelogram represents the gameto- phyte and the unshaded part the sporophyte. Among the 154 PLANT STRUCTURES lowest plants the gametophyte is represented by the whole plant structure. When the sporophyte first appears it is dependent upon the gametophyte (some Thallophytes and the Bryophytes), and is relatively inconspicuous. Later the sporophyte becomes independent (most Pteridophytes), the gametophyte being relatively inconspicuous. Finally (heterosporous Pteridophytes) the gametophyte becomes dependent upon the sporophyte, and in Spermatophytes is so inconspicuous and concealed that it is only observed by means of laboratory appliances, while the sporophyte is the whole plant of ordinary observation. CHAPTER X THE GREAT GROUPS OF PTERIDOPHYTES 82. The great groups—At least three independent lines of Pteridophytes are recognized: (1) Filicales (Ferns), (2) Equisetales (Scouring rushes, Horsetails), and (3) Ly- copodiales (Club-mosses). The Ferns are much the most abundant, the Club-mosses are represented by a few hun- dred forms, while the Horsetails include only about twenty- five species. These three great groups are so unlike that they hardly seem to belong together in the same division of the plant kingdom. Frnicaes (/erns) 83. General characters—The Ferns were used in the preceding chapter as types of Pteridophytes, so that little need be added. They well deserve to stand as types, as they contain about four thousand of the four thousand five hundred species belonging to Pteridophytes. Although found in considerable numbers in temperate regions, their chief display is in the tropics, where they form a striking and characteristic feature of the vegetation. In the trop- ics not only are great masses of the low forms to be seen, from those with delicate and filmy moss like leaves to those with huge leaves, but also tree forms with cylindrical trunks encased by the rough remnants of fallen leaves and sometimes rising to a height of thirty-five to forty-five feet, with a great crown of leaves fifteen to twenty feet long (Fig. 120). 155 ‘TITMAIVO —"(punru 2uojhv)) Dpunusg) surdj Jo yueq vy" SEE OL THE GREAT GROUPS OF PTERIDOPHYTES 157 There are also epiphytic forms (air plants)—that is, those which perch “upon other plants” but derive no nourishment from them (Fig. 112). This habit belongs chiefly to the warm and moist tropics, where the plants can absorb sufficient moisture from the air without send- ing roots into the soil. In this way many of the tropical ferns are found growing upon living and dead trees and other plants. In the temperate regions the chief epi- phytes are Lichens, Liverworts, and Mosses, the Ferns be- ing chiefly found in moist woods and ravines (Fig. 132), although a number grow in comparatively dry and exposed situations, sometimes covering extensive areas, as the com- mon brake (Péeris) (Fig. 125). The Filicales differ from the other groups of Pterido- phytes chiefly in having few large leaves, which do chloro- phyll work and bear sporangia. In a few of them there isa differentiation of functions in foliage branches and sporo- phyll branches (Figs. 127-180), but even this is excep- tional. Another distinction is that the stems are un- branched. 84. Origin of sporangia—An important feature in the Ferns is the origin of the sporangia. In some of them a sporangium is developed from a single epidermal cell of the leaf, and is an entirely superficial and generally stalked affair (Fig. 118, 5) ; in others the sporangium in its devel- opment involves several epidermal and deeper cells of the leaf, and is more or less of an imbedded affair. In the first case the ferns are said to be leptosporangiate ; in the sec- ond case they are eusporangiate. The leptosporangiate Ferns are overwhelmingly abun- dant as compared with the Eusporangiates. Back in the Coal-measures, however, there was an abundant fern vege- tation which was probably all eusporangiate. The Lep- tosporangiates seem to be the modern Ferns, the once abundant Enusporangiates being represented now in the temperate regions only by such forms as moonwort (Bo- 158 PLANT STRUCTURES trychium) (Fig. 129) and adder’s tongue (Ophioglossum) (Fig. 130). It is important to note, however, that the Horsetails and Club-mosses are Eusporangiates, as well as all the Seed-plants. Another small but interesting group of Ferns includes the ‘‘ Water-ferns,” floating forms or sometimes on muddy flats. The common Jursilia may be taken as a type (Fig. 133). The slender creeping stem sends down numerous roots into the mucky soil, and at intervals gives rise to a comparatively large leaf. This leaf has a long erect petiole and a blade of four spread- Fig. 133.—A water-fern (Marsilia), Fie. 184. One of the floating water-ferns (Sa?- showing horizontal stem, with vinia), showing side view (4) and view from descending roots, and ascend- above (B). The dangling root-like processes ing leaves; a, a young leaf are the modified submerged leaves. In A, showing circinate vernation ; near the top of the cluster of submerged 8,8, 8porophyl]l branches (‘‘spo- leaves, some sporophyll branches (‘‘ sporo- rocarps"’).—After BIscHorr. carps’’) may be seen.—After BiscHorr. ing wedge-shaped leaflets like a “ four-leaved clover.’ The dichotomous venation and circinate vernation at once sug- gest the fern alliance. From near the base of the petiole THE GREAT GROUPS OF PTERIDOPHYTES 159 another leaf branch arises, in which the blade is modified as a sporophyll. In this case the sporophyll incloses the sporangia and becomes hard and nut-like. Another com- mon form is the floating Salvinia (Fig. 134). The chief interest lies in the fact that the water-ferns are heteros- porous. As they are leptosporangiate they are thought to have been derived from the ordinary leptosporangiate Ferns, which are homosporous. Three fern groups are thus outlined: (1) homosporous- eusporangiate forms, now almost extinct ; (2) homosporous- leptosporangiate forms, the great overwhelming modern group, not only of Filicales but also of Pteridophytes, well called true Ferns, and thought to be derived from the pre- ceding group; and (3) heterosporous-leptosporangiate forms, the water-ferns, thought to be derived from the pre- ceding group. EQuiseraves (Horsetatls or Scouring rushes) 85. General characters—The twenty-five forms now rep- resenting this great group belong to a single genus (Hquwise- tum, meaning ‘‘horsetail”), but they are but the linger- ing remnants of an abundant flora which lived in the time of the Coal-measures, and helped to form the forest vegeta- tion. The living forms are small and inconspicuous, but very characteristic in appearance. They grow in moist or dry places, sometimes in great abundance (Fig. 135). The stem is slender and conspicuously jointed, the joints separating easily; it is also green and fiuted with small longitudinal ridges ; and there is such an abundant deposit of silica in the epidermis that the plants feel rough. This last property suggested its former use in scouring, and its name ‘‘ scouring rush.” At each joint is a sheath of minute leaves, more or less coalesced, the individual leaves some- times being indicated only by minute teeth. This arrange- ment of leaves in a circle about the joint is called the cyclic Fie. 135. Equisetum arvense, a common horsetail: 1, three fertile shoots rising from the dorsiventral stem, showing the cycles of coalesced scale-leaves at the joints and the terminal strobili with numerous sporophylls, that at a@ being mature; 2, a sterile shoot from the same stem, showing branching; 3, a single peltate sporo- phyll bearing sporangia; 4, view of sporophyll from beneath, show ing dehiscence of sporangia; 5, 6, 7, spores, showing the unwinding of the outer coat, which aids in dispersal.—After WossIDLo, THE GREAT GROUPS OF PTERIDOPHYTES 161 arrangement, or sometimes the whorled arrangement, each such set of leaves being called a cycle or a whorl. These leaves contain no chlorophyll and have evidently abandoned chlorophyll work, which is carried on by the green stem. Such leaves are known as sca/es, to distinguish them from foliage leaves. The stem is either simple or profusely branched (Fig. 135). st. The strobilus.—One of the distinguishing characters of the group is that chlorophyll-work and spore-formation are completely differentiated. Although the foliage leaves Fie. 136. Dicecious gametophytes of Hguisetum:; A. the female gametophyte, show- ing branching, rhizoids. and an archegonium (ar); B, the male gametophyte, showing several antheridia ( 2 ).—After CAMPBELL. are reduced to scales, and the chlorophyll-work is done by the stem, there are well-organized sporophylls. The sporo- phylls are grouped close together at the end of the stem in a compact conical cluster which is called a strodilus, the Latin name for “pine cone,” which this cluster of sporo- phylis resembles (Fig. 135). Each sporophyll consists of a stalk-like portion and a shield-like (peltate) top. Beneath the shield hang the 162 PLANT STRUCTURES sporangia, which produce spores of but one kind, hence these plants are homosporous ; and as the sporangia origi- nate in eusporangiate fashion, Ayuisetum has the homospo- rous-eusporangiate combination shown by one of the Fern groups. It is interesting to know, however, that some of the ancient, more highly organized members of this group were heterosporous, and that the present forms have dicecious gametophytes (Fig. 136). LycopopiaLes (('Jub-mosses) 87. General characters—This group is now represented by about five hundred species, most of which belong to the two genera Lycopodium and Selaginella, the latter being much the larger genus. The plants have slender, branching, prostrate, or erect stems completely clothed with small foliage leaves, having a general moss-like appearance (Fig. 137). Often the erect branches are terminated by conspicuous conical or cylindrical strobili, which are the ‘‘ clubs” that enter into the name ‘ Club- mosses.” There is also a certain kind of resemblance to miniature pines, so that the name ‘‘ Ground-pines” is sometimes used. Lycopodiales were once much more abundant than now, and more highly organized, forming a conspicuous part of the forest vegetation of the Coal-measures. One of the distinguishing marks of the group is that the sperm does not resemble that of the other Pteridophytes, but is of the Bryophyte type (Fig. 140, 7’). That is, it consists of a small body with two cilia, instead of a large spirally coiled body with many cilia. Another distinguish- ing character is that there is but a single sporangium pro- duced by each sporophyll (Fig. 137). This is in marked contrast with the Filicales, whose leaves bear very numer- ous sporangia, and with the Equisetales, whose sporophylls bear several sporangia. THE GREAT GROUPS OF PTERIDOPHYTES 163 Fic. 187. A common club-moss (Lycopodium clavatum): 1, the whole plant, showing horizontal stem giving rise to roots and to erect branches bearing strobili; 2, a single sporophyll with its sporanginm; 3, spores, much magnified.—After Wos- SIDLO. 88. Lycopodium.—This genus contains fewer forms than the other, but they are larger and coarser and more charac- teristic of the temperate regions, being the ordinary Club- mosses (Fig. 137). They also more commonly display conspicuous and distinct strobili, although there is every 164 PLANT STRUCTURES gradation between ordinary foliage leaves and distinct sporophylls. The sporangia are borne either by distinct sporophyils or by the ordinary foliage leaves near the summit of the stem. At the base of each of these leaves, or sporophylls, on the upper side, is a single sporangium (Fig. 137). The sporangia are eusporangiate in origin, and as the spores are all alike, Lycopodium has the same homosporous-eusporan- giate combination noted in Equisetales and in one of the groups of Filicales. 89. Selaginella—This large genus contains the smaller, more delicate Club-mosses, often being called the “ little Club-mosses.” They are especially displayed in the trop- Fie. 188, Selaginella, showing general spray-like habit, and dangling leafless stems which strike root (rhizophores).—From “ Plant Relations.” ics, and are common in greenhouses as delicate, mossy, decorative plants (Fig. 138). In general the sporophylls are not different from the ordinary leaves (Fig. 139), but sometimes they are modified, though not so distinct as in certain species of Lycopodium. THE GREAT GROUPS OF PTERIDOPHYTES 165 The solitary sporangium appears in the azils (upper angles formed by the leaves with the stem) of the leaves and sporophylls, but arise from the stem instead of the Fic. 139. Selaginella Martensii; A, branch bearing strobili; B, a microsporophy]] with a microsporangium, showing microspores through a rupture in the wall; C, a megasporophyll with a megasporangium ; J, megaspores: Z£, microspores.— CALDWELL. 29 166 PLANT STRUCTURES leaf (Fig. 139). This is important as showing that sporan- gia may be produced by stems as well as by leaves, those being produced by leaves being called foliar, and those by stem cauline. The most important fact in connection with Selaginella, however, is that it is heterosporous. Megasporangia, each usually containing but four megaspores, are found in the axils of a few of the lower leaves of the strobilus, and more numerous microsporangia occur in the upper axils, con- taining very many microspores (Fig. 139). The character of the gametophytes of heterosporous Pteridophytes may be well illustrated by those of Selaginella. The microspore germinates and forms a male gameto- phyte so small that it is entirely included within the spore Fig. 140 Male gametophyte of Selaginella; in each case p is the prothallial cell, w the wall cells of the antheridium, s the sperm tissue: 7, the bicilfate sperms.— After BELAJEFF. wall (Fig. 140). A single small cell is all that represents the ordinary cells of the prothallium, while all the rest is an antheridium, consisting of a wall of a few cells sur- rounding numerous sperm mother cells. In the presence THE GREAT GROUPS OF PTERIDOPHYTES 167 of water the antheridium wall breaks down, as also do the walls of the mother cells, and the small biciliate sperms are set free. The much larger megaspores germinate and become filled with a mass of numerous nutritive cells, representing the ordinary cells of a prothallium (Fig. 141). The spore wall is broken by this growing prothallium, a part of which thus protrudes and becomes exposed, although the main part of it is still invested by the old megaspore wall. In this exposed portion of the female gameto- phyte the archegonia appear, and thus be- come accessible to the sperms. In the case of Isoetes (see § 90) the reduction of the female gametophyte is even greater, as it does not project from the megaspore wall at all, and the archegonia are made accessible through cracks in the wall immediately over Fie. 141. Female gametophyte of a Selaginella: spm, wall of megaspore ; pr, gametophyte; them. ar, an archegonium; emd, and eh, em- The embryo of Se- bryo sporophytes ; «f, suspensors ; the gam- ‘5 3 a etophyte bas developed a few rhizoids,— laginella is also impor- ‘After Prnken: tant to consider. Be- ginning its development in the venter of the archegonium, it first hes upon the exposed margin of the prothallium, while the mass of nutritive cells lie deep within the mega- spore (Fig. 141, emd,, emb,). It first develops an elongated cell, or row of cells, which thrusts the embryo cell deeper among the nutritive cells. This cell or row of cells, formed by the embryo to place the real embryo cell in better rela- 168 PLANT STRUCTURES tion to its food supply, is called the suspensor, and is a temporary organ of the embryo (Figs. 141, 142, et). At the end of the suspensor the real embryo develops, and when its regions become organized it shows the following parts: (1) a large foot buried among the nutritive cells of the prothallium and absorbing nourishment; (2) a root stretching out toward the substratum ; (3) a stem extend- CPS TK » Soeclibem tp, Fig. 142. Embryo of Selaginella removed from the gametophyte, showing suspensor (et), root-tip (w), foot (f), cotyledons (dl), stem-tip (s¢), and ligules (/ég).—After PFEFFER. ing in the other direction, and bearing just behind its tip (4) a pair of opposite leaves (cotyledons) (Fig. 142). As the sporangia of Selayinella are eusporangiate, this genus has the heterosporous-eusporangiate combination—a combination not mentioned heretofore, and being of special interest as it is the combination which belongs to all the Spermatophytes. For this and other reasons, Selaginella is one of the Pteridophyte forms which has attracted special attention, as possibly representing one of the an- cestral forms of the Seed-plants. THE GREAT GRUUPS OF PTERIDOPHYTES 169 90. Isoetes—This little group of aquatic plants, known as “‘quillworts,” is very puzzling as to its relationships among Pteridophytes. By some it is put with the Ferns, forming a distinct division of Filicales ; by others it is put \ y i ‘ Lak LAN Lf AW ANS PAINS Aye i VAAN Fig. 143. A common quillwort (Jsoetes lacus- Fie. 144. Sperm of Isoetes, show- tris), showing cluster of roots dichoto- ing spiral body and seven long mously branching, and cluster of leaves cilia arising from the beak.— each enlarged at base and inclosing a sin- After BELAJEFF. gle sporangium.—After ScHENCK. with the Club-mosses, and is associated with Selayinella. It resembles a bunch of fine grass growing in shoal water or in mud, but the leaves enlarge at the base and overlap one another and the very short tuberous stem (Fig. 143). Within each enlarged leaf base a single sporangium is formed, and the cluster contains both megasporangia and microsporangia. The sporangia are eusporangiate, and therefore Jscetes shares with Selaginella the distinction of 170 PLANT STRUCTURES having the heterosporous-eusporangiate combination, which is a feature of the Seed-plants. The embryo is also peculiar, and is so suggestive of the embryo of the Monocotyledons (see § 114) among Seed- plants that some regard it as possibly representing the ancestral forms of that group of Spermatophytes. The peculiarity lies in the fact that at one end of the axis of the embryo is a root, and at the other the first leaf (cotyledon), while the stem tip rises as a lateral outgrowth. This is exactly the distinctive feature of the embryo of Monocoty- ledons. The greatest obstacle in the way of associating these quillworts with the Club-mosses is the fact that their sperms are of the large and spirally coiled multiciliate type which belongs to Filicales and Equisetales (Fig. 144), and not at all the small biciliate type which characterizes the Club- mosses (Fig. 140). To sum up, the short unbranched stem with comparatively few large leaves, and the coiled multi- ciliate sperm, suggest Filicales; while the solitary spo- rangia and the heterosporous-eusporangiate character sug- gest Selaginella. CHAPTER XI SPERMATOPHYTES: GYMNOSPERMS 91. Summary from Pteridophytes.—In considering the important contributions of Pteridophytes to the evolution of the plant kingdom the following seem worthy of note : (1) Prominence of sporophyte and development of vuscu- lar system.—This prominence is associated with the display of leaves for chlorophyll work, and the leaves necessitate the work of conduction, which is arranged for by the vas- cular system. This fact is true of the whole group. (2) Differentiation of sporuphylls.—The appearance of sporophylls as distinct from foliage leaves, and their or- ganization into the cluster known as the strobilus, are facts of prime importance. This differentiation appears more or less in all the great groups, but the strobilus is distinct only in Horsetails and Club-mosses. (3) Introduction of heterospory and reduction of gameto- phytes.—Heterospory appears independently in all of the three great groups—in the water-ferns among the Fili- cales, in the ancient horsetails among the Equisetales, and in Seluginella and Jsoetes among Lycopodiales. All the other Pteridophytes, and therefore the great majority of them, are homosporous. The importance of the appear- ance of heterospory lies in the fact that it leads to the development of Spermatophytes, and associated with it is a great reduction of the gametophytes, which project little, if at all, from the spores which produce them. 92. Summary of the four groups—It may be well in this connection to give certain prominent characters which will 171 172 PLANT STRUCTURES serve to distinguish the four great groups of plants. It must not be supposed that these are the only characters, or even the most important ones in every case, but they are convenient for our purpose. Two characters are given for each of the first three groups—one a positive character which belongs to it, the other a negative character which distinguishes it from the group above, and becomes the positive character of that group. (1) Thallophytes.—Thallus body, but no archegonia. (2) Bryophytes.—Archegonia, but no vascular system. (3) Pteridephytes.—Vascular system, but no seeds. (+) Spermatophytes.—Seeds. 93. General characters of Spermatophytes.—This is the greatest group of plants in rank and in display. So con- spicuous are they, and so much do they enter into our experience. that they have often been studied as ‘‘ botany,” to the exclusion of the other groups. The lower groups are not meiely necessary to fill out any general view of the plant kingdom, but they are absolutely essential to an understanding of the structures of the highest group. This great dominant group has received a variety of names. Sometimes they are called .{nxthophytes, meaning “Flowering plants,” with the idea that they are distin- guished by the production of “flowers.” A flower is diffi- cult to define, but in the popular sense all Spermatophytes do not produce flowers, while in another sense the strobilus of Pteridophytes is a flower. Hence the flower does not accurately limit the group, and the name Anthophytes is not in general use. Much more commonly the group is called Phanerogams (sometimes corrupted into Phenogams or even Phenogams), meaning ‘evident sexual reproduc- tion.” At the time this name was proposed all the other groups were called Crypfogams, meaning “hidden sexual reproduction.” It is a curious fact that the names ought to have been reversed, for sexual reproduction is much more evident in Cryptogams than in Phanerogams, the mistake SPERMATOPHYTES: GYMNOSPERMS 1%3 arising from the fact that what were supposed to be sexual organs in Phanerogams have proved not to be such. The name Phanerogam, therefore, is being generally abandoned ; but the name Cryptogam is a useful one when the lower groups are to be referred to; and the Pteridophytes are still very frequently called the Vascular Cryptogams. The most distinguishing mark of the group seems to be the production of seeds, and hence the name Spermatophytes, or ‘** Seed-plants,” is coming into general use. The seed can be better defined after its development has been described, but it results from the fact that in this group the single megaspore is never discharged from its megasporangium, but germinates just where it is devel- oped. The great fact connected with the group, therefore, is the retention of the megaspore, which results in a seed. The full meaning of this will appear later. There are two very independent lines of Seed-plants, the Gymnosperms and the Angiosperms. The first name means ‘‘naked seeds,” referring to the fact that the seeds are always exposed; the second means ‘‘inclosed seeds,” as the seeds are inclosed in a seed vessel. GYMNOSPERMS 94. General characters—The most familiar Gymnosperms in temperate regions are the pines, spruces, hemlocks, cedars, etc., the group so commonly called ‘‘ evergreens.” It is an ancient tree group, for its representatives were associated with the giant club-mosses and horsetails in the forest vegetation of the Coal-measures. Only about four hundred species exist to-day as a remnant of its for- mer display, although the pines still form extensive forests. The group is so diversified in its structure that all forms can not be included in a single description. The common pine (Pinus), therefore, will be taken as a type, to show the general Gymnosperm character. 174 PLANT STRUCTURES 95, The plant body.—The great body of the plant, often forming a large tree, is the sporophyte; in fact, the gametophytes are not visible to ordinary observation. It should be remembered that the sporophyte is distinctly a sexless generation, and that it develops no sex organs. This great sporophyte body is elaborately organized for nutritive work, with its roots, stems, and leaves. These organs are very complex in structure, being made up of various tissue systems that are organized for special kinds of work. The leaves are the most variable organs, being differentiated into three distinct kinds—(1) foliage leaves, (2) scales, and (3) sporophylls. 96. Sporophylls——The sporophylls are leaves set apart to produce sporangia, and in the pine they are arranged in a strobilus, as in the Horsetails and Club-mosses. As the group is heterosporous, however, there are two kinds of sporophylls and two kinds of strobili. One kind of strobilus is made up of megasporophylls bearing mega- sporangia ; the other is made up of microsporophylls bear- ing microsporangia. These strobili are often spoken of as the “‘ flowers” of the pine, but if these are flowers, so are the strobili of Horsetails and Club-mosses. 97. Microsporophylls—In the pines the strobilus com- posed of microsporophylls is comparatively small (Figs. 145, /, 164). Each sporophyll is like a scale leaf, is nar- rowed at the base, and upon the lower surface are borne two prominent sporangia, which of course are microspo- rangia, and contain microspores (Fig. 146). These structures of Need-plants all received names before they were identified with the corresponding struc- tures of the lower groups. The microsporophyll was called a stumen, the microsporangia pollen-saes, and the microspores pollen grains, or simply pollen, These names are still very convenient to use in connection with the Spermatophytes, but it should be remembered that they are simply other names for structures found in the lower groups. Fie. 145. Pinus Laricio, showing tip of branch bearing needle-leaves, scale-leaves, and cones (strobili): @, very young carpellate cones. at time of pollination, borne at tip of the young shoot upon which new leaves are appearing; 5, carpellate cones one year old; ¢, carpellate cones two years old, the scales spreading and shedding the seeds; d, young shoot bearing a cluster of staminate cones.—CaLDWELL. 176 PLANT STRUCTURES The strobilus composed of microsporophylls may be called the stamitnate strobilus—that is, one composed of stamens; it is often called the staminate cone, “‘ cone” being the English translation of the word “strobilus.” Frequently the staminate cone is spoken of as the ‘‘ male cone,” as it was once supposed that the stamen is the Fie. 146. Staminate cone (strobilus) of pine (Pinus): A, section of cone, showing microsporophylls (stamens) bearing microsporangia; B, longitudinal section of a single stamen, showing the large sporangium beneath; (C, cross-section of a sta- men, showing the two sporangia; D, a single microspore (pollen grain) much en- larged, showing the two wings, and a male gametophyte of two cells, the lower and larger (wall cell) developing the pollen tube, the upper and smaller (genera- tive cell) giving rise to the sperms.—After SciuMPER. male organ. This name should, of course, be abandoned, as the stamen is now known to be a microsporophyll, which is an organ produced by the sporophyte, which never pro- duces sex organs. It should be borne distinctly in mind that the stamen is not a sex organ, for the literature of botany is full of this old assumption, and the beginner is in SPERMATOPHYTES: GYMNOSPERMS 7% danger of becoming confused and of forgetting that pollen grains are asexual spores. 98. Megasporophylls—The strobili composed of mega- sporophylls become much larger than the others, forming Fie. 147. Pinus sylvestris, showing mature cone partly sectioned, and showing car- pels (sg, sg}, sg?) with seeds in their axils (g), in which the embryos (e771) may be distinguished; 1, a young carpel with two megaspcrangia; B, an old carpel with mature seeds (ch), the micropyle being below (J/).—After BEssEY. the well-known cones so characteristic of pines and their allies (Figs. 145, a, 6, c, 163). Each sporophyll is some- what leaf-like, and at its base upon the upper side are two megasporangia (Fig. 147). It is these sporangia which are peculiar in each producing and retaining a solitary large megaspore. This megaspore resembles a sac-like cavity in 178 PLANT STRUCTURES the body of the sporangium (Fig. 148, 7), and was at first not recognized as being a spore. These structures had also received names before they were identified with the corresponding structures of the lower groups. The megasporophyll was called a carpet, the megasporangia ovules, and the megaspore an embryo- sac, because the young embryo was observed to develop within it (Fig. 147, em). The strobilus of megasporophylls, therefore, may be ealled the carpellate strobilus or curpellate cone. As the carpel enters into the organization of a structure known as the pistil, to be described later, the cone is often called the pistillate cone, As the staminate cone is sometimes wrongly called a ‘‘male cone,” so the carpellate cone is wrongly called a ‘‘female cone.” the old idea being that the carpel with its ovules represented the female scx organ. The structure of the megaspo- rangium, or ovule, must be known. The main body is the nucellus (Figs. 148, ¢, 149, nc); this sends out from near its base an outer membrane (ufegument) which is distinct above (Figs. 148 6, 149 7), covering the main part of the nucellus and projecting ‘esti Bee. erate beyond its apex as a prominent neck, carpel structures of pine, the passage through which to the apex corn ie a of the nucellus is called the mirropyle ovule CB). inwhich ame CC Little. Bate) (Mie, 44s; @). Dens seen the micropyle «@, — trally placed within the body of the integument (7), nncellus é : (©), embryo sac or megn. TUCellus is the conspicuous cavity spore ().—Carpwett. called the embryo-sac (Fig. 148, «/), in reality the retained megaspore. The relations between integument, micropyle, nucellus, and embryo-sac should be kept clearly in mind. In the SPERMATOPHYTES: GYMNOSPERMS 179 pine the micropyle is directed downward, toward the hase of the sporophyll (Figs. 147, 148). 99. Female gametophyte—The female gametophyte is always produced by the germination of a megaspore, and therefore it should be produced by the sc- called embryo-sae with- in the ovule. This im- bedded megaspore ger- minates, just as does the megaspore of v- laginella or Isoetes, by cell division becoming filled with a compact mass of nutritive tissue representing the ordi- nary cells of the female prothallium (Fig. 149, e). This prothallium naturally does not protrude beyond the boundary of the mega- spore wall, beg com- pletely surrounded by the tissues of the sporangium. It must be evident that this gametophyte is abso- lutely dependent upon the sporophyte for its nutrition, and remains not merely attached to it, but is actually im- bedded within its tis- Fie. 149. Diagrammatic section through ovule (megasporangium) of spruce (Picea), showing integument (i), nucellus (7c), endosperm or female gametophyte (e) which fills the large megaspore imbedded in the nucellus, two archegonia (@) with short neck (¢) and. venter containing the egg (0), and position of ger- minating pollen grains or microspores (p) whose tubes (f) penetrate the nucellus tissue and reach the archegonia,—After “i HIIPER. sues like an internal parasite. So conspicuous a tissue within the ovule, as well as in the seed into which the 180 PLANT STRUCTURES ovule develops, did not escape early attention, and it was called endosperm, meaning ‘‘ within the seed.” The endo- sperm of Gymnosperms, therefore, is the female gameto- phyte. At the margin of the endosperm nearest the micropyle regular flask-shaped archegonia are developed (Fig. 149, «), making it sure that the endosperm is a female gameto- phyte. It is evident that the necks of these archegonia (Fig. 149, c) are shut away from the approach of sperms by swimming, and that some new method of approach must be developed. 100. Male gametophyte.—The microspores are developed in the sporangium in the usual tetrad fashion, and are pro- duced and scattered in very great abundance. It will be remembered that the male gametophyte developed by the microspore of Selaginella is contained entirely within the spore, and consists of a single ordinary prothallial cell and one antheridium (see § 89). In the pine it is no bet- ter developed. One or two small cells appear, which may be regarded as representing prothallial cells, while the rest of the gametophyte seems to be a single antheridium (Fig. 146, D). At first this antheridium seems to consist of a large cell called the wall cell, and a small one called the generative cell. Sooner or later the generative cell divides and forms two small cells, one of which divides again and forms two cells called mule cells. which seem to represent the sperm mother cells of lower plants. The three active cells of the completed antheridium, therefore. are the wall cell, with a prominent nucleus, and two small male cells which are free in the large wall cell. These sperm mother cells (male cells) do not form sperms within them, as there is no water connection be- tween them and the archegonia, and a new method of transfer is provided. This is done by the wall cell, which develops a tube, known as the podlen-fube. Into this tube the male cells enter, and as it penetrates among the cells SPERMATOPHYTES: GYMNOSPERMS 181 which shut off the archegonia it carries the male cells along, and so they are brought to the archegonia (Fig. 150). Fic. 150. Tip of pollen tube of pine, Fic. 151. Pollen tube passing through the showing the two male cells (4, B), neck of an archegonium of spruce (Picea), two nuclei ((’) which accompany and containing near its tip the two male them, and the numerous food nuclei, which are to be discharged into the granules (D): the tip of the tube egg whose cytoplasm the tube is just en- is just about to enter the neck of tering.—After STRASBURGER. the archegonium,—CaLDWELL. 101. Fertilization.—Before fertilization can take place the pollen-grains (microspores) must be brought as near as possible to the female gametophyte with its archegonia. The spores are formed in very great abundance, are dry and powdery, and are scattered far and wide by the wind. In the pines and their allies the pollen-grains are winged (Fig. 146, D), so that they are well organized for wind dis- tribution. This transfer of pollen is called pollination, and those plants that use the wind as an agent of transfer are said to be anemophilous, or ‘* wind-loving.” The pollen must reach the ovule, and to insure this it must fall like rain. To aid in catching the falling pollen the scale-like carpels of the cone spread apart, the pollen grains slide down their sloping surfaces and collect in a 30 182 PLANT STRUCTURES little drift at the bottom of each carpel, where the ovules are found (Fig. 147, A, B). The flaring lips of the micro- pyle roll inward and outward as they are dry or moist, and by this motion some of the pollen-grains are caught and pressed down upon the apex of the nucellus. In this position the pollen-tube develops, crowds its way among the cells of the nucellus, reaches the wall of the embryo-sac, and penetrating that, reaches the necks of the archegonia (Fig. 149, p, ¢); crowding into them (Fig. 151), the tip of the tube opens, the male cells are Fie. 152. Fertilization in spruce (Picea): B is an egg, in the tip of which a pollen tube (p) has entered and has discharged into the cytoplasm a male nucleus (sz), which is to unite with the egg (female) nucleus (on); C, a later stage in which the two nuclei are uniting.—After ScHIMPER. discharged, one male cell fuses with the egg (Fig. 152), and fertilization is accomplished, an oospore being formed in the venter of the archegonium. It will be noticed that the cell which acts as a male gamete is really the sperm mother cell, which does not organize a sperm in the absence of a water connection. This peculiar method of transferring the male cells by means of a special tube developed by the antheridium is SPERMATOPHYTES: GYMNOSPERMS 183 called siphonogamy, which means “sexual reproduction by means of a tube.” So important is this character among Spermatophytes that some have proposed to call the group Siphonogams. 102. Development of the embryo.—The oospore when formed lies at the surface of the endosperm (female gameto- phyte) nearest to the micropyle. As the endosperm is to supply nourishment to the em- bryo, this position is not the most favorable. Therefore, as in Selaginella, the oospore first develops a suspensor, which in pine and its allies becomes very long and often tortuous (Fig. 153, d,s). At the tip of the suspensor the cell or cells (em- bryo cells) which are to develop the embryo are carried (Fig. 153, dA, ka), and thus become deeply buried, about centrally placed, in the endosperm. Fie. 153. Embryos of pine: A, Several suspensors may start very young embryos (ka) at the from as many archegonia in the tips of long and contorted sus- pensors (s); B, older embryo, same ovule, and several embryos showing attachment to snspen- may begin to develop, but as a sor (x), the extensive root sheath I A d th (wh), root tip (ws), stem tip rule only one survives, an e Go) anil eoiyledons qi -Ater solitary completed embryo (Fig. STRASBURGER. 153, B) les centrally imbedded in the endosperm (Fig. 153). The development of more than one embryo in a megasporangium (ovule)is called polyembryony, a phenomenon natural to Gymnosperms with their several archegonia upon a single gametophyte. 103. The seed.—While the embryo is developing some important changes are taking place in the ovule outside of the endosperm. The most noteworthy is the change which transforms the integument into a hard bony covering, 184 PLANT STRUCTURES known as the seed coat, or testa (Fig. 153a). The devel- opment of this testa hermetically seals the structures with- in, further development and activity are checked, and the living cells pass into the resting condition. This pro- Fie. 158. Pine seca, tected structure with its dormant cells is the seed. In a certain sense the seed is a transformed ovule (mega- sporangium), but this is true only as to its outer configura- Fra. 154. Pine seedlings, showing the long hypocotyl and the numerous cotyledons, with the old seed case still attached.—After ATKINSON, SPERMATOPHYTES: GYMNOSPERMS 185 tion. If the internal structures be considered it is much more. It is made up of structures belonging to three gen- erations, as follows: (1) The old sporophyte is represented by seed coat and nucellus, (2) the endosperm is a gameto- phyte, while (3) the embryo is a young sporophyte. It can hardly be said that the seed is simple in structure, or that any real conception of it can be obtained without approach- ing it by way of the lower groups. The organization of the seed checks the growth of the embryo, and this development within the seed is known as Fie. 155. A cycad, showing the palm-like habit. with much branched leaves and scaly stem.—From “ Plant Relations.” the intra-seminal development. In this condition the em- bryo may continue for a very long time, and it is.a ques- tion whether it is death or suspended animation. Is a seed alive ? is not an easy question to answer, for it may be kept in a dried-out condition for years, and then when placed in suitable conditions awaken and put forth a living plant. “TIEMMTVY Q— SAARI] aBBI[OJ plo Surpwaids Lpopra oyy aay asoyy MOTaq pur ‘png Ul Weyy paiaaod YT S9avol o[WOS OY} AB MOL ‘soALAT BBBI[OS Sunod JU Lo}SNfI Jood APAVoU otf} ST sooo oY] UT “Ways oy} JO JLWITUNS oY] 7B ASVIOF OY BuLMOYS “Ysjouas svg “9ST “OTA SPERMATOPHYTES: GYMNOSPERMS 187 This ‘‘ awakening ” of the seed is spoken of as its ‘‘ ger- mination,” but this must not be confused with the germi- nation of a spore, which is real germination. In the case of the seed an oospore has germinated and formed an embryo, which stops growing for a time, and then resumes it. This resumption of growth is not germination, but is what Fie. 157. Tip of pollen tube of Cycas revoluta, containing the two spiral, multiciliate sperms.—After IKENO. happens when a seed is said to ‘‘ germinate.” This second period of development is known as the exfra-seminal, for it is inaugurated by the escape of the sporophyte from the seed (Fig. 154). 104. The great groups of Gymnosperms.—There are at least four living groups of Gymnosperms, and two or three Fig. 158. A pine (Pinus) showing the central shaft and also the bunching of the needle leaves toward the tips of the branches.—From “ Plant Relations.” SPERMATOPHYTES: GYMNOSPERMS 189 extinct ones. The groups differ so widely from one an- other in habit as to show that Gymnosperms can be very much diversified. They are all woody forms, but they may be trailing or straggling shrubs, gigantic trees, or high-climbing vines ; and their leaves may be nee- dle-like, broad, or ‘‘ fern- like.” For our purpose it will be only necessary to define the two most prom- inent groups. 105. Cycads, — Cycads are tropical, fern - like forms, with large branched (compound) leaves. The stem is either a columnar shaft crowned with a ro- sette of great branching leaves, with the general habit of tree-ferns and palms (Figs. 155, 156); or they are like great tu- bers, crowned in the same way. In ancient times (the Mesozoic) they were very abundant, forming a conspicuous feature of the vegetation, but now they are represented only by about eighty forms scattered through both the oriental and occiden- tal tropics. Fie. 159. The giant redwood (Sequoia gi- They are very fern- gantea) of California: the relative size ; s is indicated by the figure of a man stand- like in structure as well ing at the right.—After WILL1amson. 190 PLANT STRUCTURES as in appearance, but they produce seeds and must be associated with Spermatophytes, and as the seed is ex- posed they are Gymnosperms. A discovery has been made Fie. 160. An araucarian pine (Araucaria), showing the central shaft, and the regular cycles of branches spreading in every direc- tion and bearing numerous small leaves.— From “ Plant Relations.” recently that strikingly emphasizes their fern- like structure. In fer- tilization a pollen-tube develops, as described for pine and its allies, but the male cells (sperm mother - cells) which it contains or- ganize sperms, and these sperms are of the coiled multiciliate type (Fig. 157) charac- teristic of all the Pter- idophytes except Club- mosses. This associa- tion of the old ciliated sperm habit with the new pollen-tube habit is a very interesting in- termediate or transition condition. It should be said that these sperms havebeen actually found in but two species of the Cycads, but there are reasons for suppos- ing that they may be found in all. Another one of the Gymnosperm groups, represented to- day only by the com- monly cultivated maid- SPERMATOPHYTES: GYMNOSPERMS 191 enhair tree (Gingko), with broad dichotomously veined leaves, also develops multiciliate sperms. The testa of the seed, instead of being entirely hard as described for pine and its allies, develops in two layers, the inner hard and bony, and the outer pulpy, making the ripe fruit resemble a plum. 106. Conifers—This is the great modern Gymnosperm group, and is characteristic of the temperate regions, where it forms great forests. Some of the forms are widely dis- tributed, as the great genus of pines (Pinus) (Fig. 158), while some are now very much restricted, although for- merly very widely distributed, as the gigantic redwoods (Sequoia) of the Pacific slope (Fig. 159). The habit of the body is quite charac- teristic, a central shaft extending continuously to the very top, while the lateral branches spread horizontally, with dimin- ishing length to the top, forming a conical outline (Figs. 160, 162). This habit of firs, pines, etc., Fie. 161.—Cross-section of a needle-leaf of gives them an appearance very distinct from that of other trees. Another peculiar fea- ture is furnished by the characteristic ‘“‘needle- pine, showing epidermis (¢) in which there are sunken stomata (sp), heavy- walled hypodermal tissue (es) which gives rigidity, the mesophyll region (7) in which a few resin-ducts (2) are seen, and the central region (stede) in which two vascular bundles.are developed.— After Sacus. leaves,” which seem to be poorly adapted for foliage. These leaves have small spread of surface and very heavy protecting walls, and show adaptation for enduring hard conditions (Fig. 161). As they have no regular period of falling, the trees are always clothed with them, and have been called ‘‘ evergreens.” There are some notable exceptions to this, however, as in Hie. 162. A larch (Zaria), showing the continuous central shatt and horizontal branches, the general outline being distinctly conical. The larch is peculiar among Conifers in periodically shedding its leaves.—From *t Plant Relations,” SPERMATOPHYTES: GYMNOSPERMS 193 the case of the common larch or tamarack, which sheds its leaves every season (Fig. 162). There are Conifers, also, which do not produce needle-leaves, as in the com- mon arbor-vite, whose leaves consist of small closely-over- lapping scale-like bodies (Fig. 163). The two types of leaf arrangement may also be noted. In most Conifers the leaves are arranged along the stem in spiral fashion, no two leaves being at the same level. This is known as the spi- ral or alternate arrange- ment. In other forms, as the cypresses, the leaves are in cycles, as was men- tioned in connection with the Horsetails, the ar- rangement being known as the cyclic or whorled. The character which gives name to the group is the ‘‘cone”—that is, the prominent carpellate cone which becomes so conspicuous in connec- Fie. 163. Arbor-vite (Thuja), showing a tion with the ripening of branch with scaly overlapping leaves, and some carpellate cones (strobili).— the seeds. These cones After EIcHen. generally ripen dry and hard (Figs. 145, 147, 163), but sometimes, as in junipers, they become pulpy (Fig. 164), the whole cone forming the so-called ‘ berry.” There are two great groups of Conifers. One, repre- sented by the pines, has true cones which conceal the 194 PLANT STRUCTURES ovules, and the seeds ripen dry. The other, represented by the yews, has exposed ovules, and the seed either ripens fleshy or has a fleshy investment. Fia. 164. The common juniper (.Jivniperus communis), the branch to the left bearing staminate strobili; that to the right bearing staminate strobili above and earpel- late strobili below, which latter have matured into the fleshy, berry-like fruit. —After Bere and Scumiprt. CHAPTER XII SPERMATOPHYTES: ANGIOSPERMS 107. Summary of Gymnosperms.—Before beginning An- giosperms it is well to state clearly the characters of Gym- nosperms which have set them apart as a distinct group of Spermatophytes, and which serve to contrast them with Angiosperms. (1) The microspore (pollen-grain) by wind-pollination is brought into contact with the megasporangium (oyule), and there develops the pollen-tube, which penetrates the nucellus. This contact between pollen and ovule implies an exposed or naked ovule and hence seed, and therefore the name “‘ Gymnosperm.” (2) The female gametophyte (endosperm) is well organ- ized before fertilization. (3) The female gametophyte produces archegonia. 108. General characters of Angiosperms,— This is the great- est group of plants, both in numbers and importance, being estimated to contain about 100,000 species, and forming the most conspicuous part of the vegetation of the earth. It is essentially a modern group, replacing the Gymnosperms which were formerly the dominant Seed-plants, and in the variety of their display exceeding all other groups. The name of the group is suggested by the fact that the seeds are inclosed in a seed case, in contrast with the exposed seeds of the Gymnosperms. These are also the true flowering plants, and the ap- pearance of true flowers means the development of an 195 196 PLANT STRUCTURES elaborate symbiotic relation between flowers and insects, through which pollination is secured. In Angiosperms, therefore, the wind is abandoned as an agent of pollen transfer and insects are used; and in passing from Gym- nosperms to Angiosperms one passes from anemophilous to entomophilous (‘‘insect-loving”) plants. This does not mean that all Angiosperms are entomophilous, for some are still wind-pollinated, but that the group is prevailingly ento- mophilous. This fact, more than anything else, has re- sulted in a vast variety in the structure of flowers, so char- acteristic of the group. 109. The plant body.—This of course is a sporophyte, the gametophytes being minute and concealed, as in Gym- nosperms. Thesporophyte represents the greatest possible variety in habit, size, and duration, from minute floating forms to gigantic trees; herbs, shrubs, trees; erect, pros- trate, climbing ; aquatic, terrestrial, epiphytic ; from a few days to centuries in duration. Roots, stems, and leaves are more elaborate and vari- ously organized for work than in other groups, and the whole structure represents the high- est organization the plant body has attained. As in the Gymnosperms, the leat is the most variously used organ, showing at least four distinct modifications: (1) foliage leaves, (2) scales, (3) sporophylls, and (4) floral leaves. The first three are present in Gymnosperms, and even in Pteri- dophytes, but floral leaves are pecul- Fre. 103. Stamens of hen. iar to Angiosperms, making the true bane (Llyoseyamus): A, flower, and being associated with en- moor view, Eee ala: tomophily. ment (7) and anther (p); B, Wack view, showing 110. Microsporophylls—The micro- the connective () be snorophyll of Angiosperms is more tween the pollen-sacs. ~ : —After ScumreEn. definitely known asa ‘‘ stamen ” than SPERMATOPHYTES: ANGIOSPERMS 197 that of Gymnosperms, and has lost any semblance to a leaf. It consists of a stalk-like portion, the filament; and a sporangia - bearing portion, the anther (Figs. 165, 167a). Fig. 166. Cross-section of anther of thorn apple (Datura), showing the four imbedded sporangia (a, p) containing microspores; the pair on each side will merge and dehisce along the depression between them for the discharge of pollen.—After FRANK. The filament may be long or short, slender or broad, or variously modified, or even wanting. The anther is simply the region of the sporophyll which bears sporangia, and is Fig. 167. Diagrammatic cross-sections of anthers: A, younger stage, showing the four imbedded sporangia, the contents of two removed, but the other two con- taining pollen mother cells (pm) surrounded by the tapetum (¢); B, an older stage, in which the microspores (pollen grains) are mature, and the pair of sporangia on each side are merging together to form a single pollen-sac with longitudinal dehiscence.—After BaiLLon and LUERSSEN. therefore a composite of sporophyll and sporangia and is often of uncertain limitation. Such a term is convenient, but is not exact or scientific. ol 198 PLANT STRUCTURES _If a young anther be sectioned transversely four sporan- gia will be found imbedded beneath the epidermis, a pair on each side of the axis (Figs. 166, 167). When they reach maturity, the paired sporangia on each side usually merge to- gether, forming two spore-containing cavities (Fig. 167, B). These are generally called ‘‘ pollen-sacs,” and each anther is said to consist of two pollen-sacs, although each sac is made up of two merged sporangia, and is not the equivalent of the pollen-sac in Gymnosperms, which is a single sporangium. Fie. 1674. Various forms of stamens: A, from Solanum, showing dehiscence by terminal pores; B, from Ardufus, showing anthers with terminal pores and “horns”; C, from Berberas; D, from Atherosperma, showing dehiscence by uplifted valves; £, from Aqvilegia, showing longitudinal dehiscence ; #, from Popowia, showing pollen-sacs near the middle of the stamen.—After ENGLER and PRaNTL. SPERMATOPHYTES: ANGIOSPERMS 199 The opening of the pollen-sac to discharge its pollen- grains (microspores) is called dehiscence, which means “a splitting open,” and the methods of dehiscence are various (Fig. 167a). By far the most common method is for the wall of each sac to split lengthwise (Fig. 168), which is called longitudinal dehiscence ; an- other is for each sac to open by a terminal pore (Fig. 167a), in which case it may be prolonged above into a tube. 111. Megasporophylls, — These are the so-called *‘ carpels” of Seed- plants, and in Angiosperms they are organized in various ways, but always so as to inclose the mega- sporangia (ovules). In the simplest cases each carpel is independent (Fig. Fig. 168. Cross-section of anther of a lily (Butomus), showing the separating walls between the members of each pair of sporangia broken down at z, forming a con- tinuous cavity (pollen sac) which opens by a longitudi- nal slit.—After Sacus. 169, 4), and is dif- ferentiated into three regions: (1) a hollow bulbous base, Fie. 169. Types of pistils: .4, three simple pistils (apocarpous), each showing ovary and style tipped with stigma; 2, a compound pistil (syncarpous), showing ovary (f), separate styles (g), and stigmas (n); C, a compound pistil (syncarpous), showing ovary (f), single style (g), and stigma ().—After Bere and ScuHmiptT. which contains the ovules and is the real seed case, known as the ovary; (2) sur- mounting this is a slender more or less elongated process, the style; and (3) usually at or near the apex of thestyle a special receptive surface for the pol- len, the stigma. In other cases several carpels to- 200 PLANT STRUCTURES gether form a common ovary, while the styles may also combine to form one style (Fig. 169, (’), or they may remain more or less distinct (Fig. 169, 2). Such an ovary may contain a single chamber, as if the carpels had united edge to edge (Fig. 170, 4); or it may contain as many chambers as there are constituent carpels (Fig. 170, 4), as though each carpel had formed its own ovary before coalescence. In ordinary phrase an ovary is either ‘‘one-celled” or ** several-celled,” but as the word “cell” has a very differ- ent application, the ovary chamber had better be called a loculus, meaning “‘a compartment.” Ovaries, A B C Fic. 170. Diagrammatic sections of ovaries: 1, cross-section of an ovary with one loculus and three carpels, the three scts of ovules said to be attached to the wall (parietal); B, cross-section of an ovary with three loculi and three carpels, the ovules being in the center (central); C, longitudinal section of B.—After Scuim- PER. therefore, may have one loculus or several loculi. Where there are several loculi each one usually represents a con- stituent carpel (Fig. 170, B); where there is one loculus the ovary may comprise one carpel (Fig. 169, 1), or several (Fig. 170, 4). There is a very convenient but not a scientific word, which stands for any organization of the ovary and the accompanying parts, and that is p/sti7. A pistil may be one carpel (Fig. 169, .!), or it may be several carpels or- ganized together (Fig. 169, B, ('), the former case being a stmple pistil, the latter a compound pistil. Tn other words, SPERMATOPHY TES: any organization of carpels which ap- pears as a single organ with one ovary ds a pistil. The ovules (megasporangia) are developed within the ovary (Fig. 170) either from the carpel wall, when they are foliar, or from the stem axis which ends within the ovary, when they are cauline (see § 89). They are similar in structure to those of Gymnosperms, with integument and micropyle, nu- cellus, and embryo-sac (megaspore), except that there are often two integu- ments, an outer and an inner (Fig. 171). ANGIOSVERMS Fic. 171. A diagrammatic section of an ovule of Angiosperms, showing outer integument (ai), inner integument (iz), micropyle (m), nucellus (k), and embryo sac or megaspore (em).—After Sacus. 112. The male gametophyte.— When the pollen-grain (microspore) germinates there is formed within it the sim- plest known gametophyte (Fig. 172). No trace of the Fie. 172, Germination of microspore (pollen grain) in duckweed (Lemna): A, mature spore with its nucleus; B, nucleus of spore dividing; C, two nuclei resulting from the division; D, a large and small cell following the nuclear division, forming the two-celled male gametophyte; #, division of smaller cell (generative) to form the two male cells; F, the two male cells completed and lying near the large tube nucleus, CALDWELL. 902 PLANT STRUCTURES ordinary nutritive cells of the gametophyte remains, and the whole structure seems to represent a single antherid- ium. At first it consists of two cells, the large wall cell and the small free generative cell (Fig. 172, 2). Later g 9: i Tr ti t Ey Hf b ai Lt Pa } ( : 2 Mi 2 ‘> : oo i k Fig. 173. Diagram of a longitudinal section through a carpel, to illustrate fertilization with all parts in place: s, stigma; g, style; 0, ovary ; ai, ii, outer and inner integuments; 7, base of nucel- lus; f, funiculus ; 4, antipodal cells; ¢, endo- sperm nucleus; 4, egg and one synergid; p, pol- len-tube, having grown from stigma and passed through the micropyle (m) to the egy.—After LUERSSEN. the generative cell di- vides (Fig. 172, £), either while in the pollen-grain or after entrance into the pol- len-tube, and two male cells (sperm mother- cells) are formed (Fig. 172, #), which do not organize sperms, but which function direct- ly as gametes. When pollination occurs, and the pollen has been transferred from the pollen-sacs to the stigma, it is de- tained by the minute papille of the stig- matic surface, which also excretes a sweet- ish sticky fluid. This fluid is a nutrient so- lution for the micro- spores, which begin to put out their tubes. A pollen-tube pene- trates through the stigmatic surface, en- ters among the tissues of the style, which is sometimes very long, slowly or rap- idly traverses the length of the style supplied with food by SPERMATOPHYTES: ANGIOSPERMS 203 its cells but not penetrating them, enters the cavity of the ovary, passes through the micropyle of an ovule, penetrates the tissues of the nucellus (if any), and finally reaches and pierces the wall of the embryo-sac, within which is the egg awaiting fertilization (Fig. 173). This remarkable ability of the pollen-tube to make its way through so much tissue, directly to the micropyle of an inclosed ovule, can only be explained by supposing that it is under the guidance of some strong attraction. 113. The female gametophyte—The megaspore (embryo- sac) occupies the same position in the ovule as in Gymno- sperms, but its germination is remarkably modified. The development of the female gametophyte shows two distinct Fic. 174. Lilium Philadelphicum; to the left a young megasporangium (ovule), showing integuments (C’), nucellus (A), and megaspore (B) containing a large nu- cleus. To the right a megaspore whose nucleus is undergoing the first division in the formation of the gametophyte.—CALDWELL. periods, separated from one another by the act of fertiliza- tion. If fertilization is not accomplished the second stage of the gametophyte is usually not developed. First period.—The megaspore nucleus divides (Fig. 174), and one nucleus passes to each end of the embryo- 204 PLANT STRUCTURES sac (Fig. 175, at left). Each of these nuclei divide (Fig. 175, at right), and two nuclei appear at each end of the sac (Fig. 175, at middle). Each of the four nuclei divide Fie. 175. Liliwmn Philadelphicum; to the left is an embryo-sac with a gametophyte nucleus in each end; to the right these two nuclei are dividing to form the two nuclei shown in each end of the sac in the middle figure.—CaLDWELL. (Fig. 176, at left), and four nuclei appear at each end (Fig. 176, at middle). When eight nuclei have appeared, nuclear division stops. Then a remarkable phenomenon occurs. One nucleus from each end, the two being called ‘+ polar nuclei,” moves toward the center of the sac, the two meet and fuse (Fig. 176, at right, C’), and a single large nucleus is the result. The three nuclei at the end of the sac nearest the micro- pyle are organized into cells, each being definitely sur- rounded by cytoplasm, but there is no wall and the cells remain naked but distinct. These three cells constitute the egg-apparatus (Fig. 176, at right, .!), the central one, which usually hangs lower in the sac than the others, being the egg, the two others being the sywergids, or ‘+ helpers.” Here, therefore, is an egg without an archegonium, a dis- tinguishing feature of Angiosperms. SPERMATOPILYTES: ANGIOSPERMS 905 The three nuclei at the other end of the sac are also or- ganized into cells, and usually have walls. These cells are known as untipodal cells (Fig. 176, at right, B). The large nucleus near the center of the sac, formed by the fusion of the two Fie. 176. Lilium Philadelphicum, showing last stages of germination of megaspore before fertilization: the embryo sac to the left contains the pair of nuclei in each end in a state of division preparatory to the stage represented by the middle figure, in which there are four nuclei at each end; the figure to the right shows an embryo- sac containing a gametophyte about ready for fertilization, with the egg apparatus (A) composed of the two synergids and egg (central and lower), the three antipo- dal cells (B), and the two polar nuclei fusing (¢’) to form the primary endosperm nucleus.—CALDWELL. polar nuclei, is known as the primary endosperm nucleus or the definitive nucleus. 206 PLANT STRUCTURES Fic. 177. Fertilization in the cotton plant, a Dicotyledon, showing the pollen tube (P) passing throngh the micropyle and con- taining a single sperm (male cell), and hay- ing entered the embryo-sac is in contact with one of the synergids (.S) on its way to the egg (#).—After Duaaar. This completes the first period of gametophyte de- velopment, and it is ready for fertilization. Fertilization. — The pollen-tube, carrying the two male cells, has passed down the style and en- tered the micropyle (Fig. 173). It then reaches the wall of the embryo-sac, pierces it, and is in con- tact with the egg-appa- ratus. Usually it passes along the side of one of the synergids (Fig. 177), feeding upon and disor- ganizing it. When it comes near the conspicu- ous nucleus of the egg, the tip of the tube breaks and one male cell is dis- charged into the cyto- plasm of the egg (Fig. 178). The egg and the male cell now fuse, and an oospore, which invests itself with a wall, is the result. Second pertod.—After fertilization the gameto- phyte begins its second period of development. The primary endosperm nucleus begins a series of divisions, and as a result SPERMATOPHYTES: ANGIOSPERMS DOT the sac becomes more or less filled with nutritive cells, which are often organized into a compact tissue (Fig. 179). These nutri- tive cells correspond to the endo- sperm of Gymnosperms, and re- ceive the same name. In Gymno- sperms, therefore, the endosperm (the nutritive body of the female gametophyte) is mainly formed before fertilization, while in An- glosperms it is mainly formed after fertilization. This means that in Angiosperms eggs are formed and fertilization takes lace in a yery youn ameto- Fie. 178. End of embryo-sac of P 2 8 8 lily (Lilium Philadelphicum): phyte, while in Gymnosperms and a pollen tube has entered the heterosporous Pteridophytes the sac and has discharged a male cell, whose nucleus is seen egss appear much later. uniting with the nucleus of The antipodal cells also proba- the egg; near the tip of the . a: lls of th tube is the disorganizing nu- bly represent nutritive cells o e cleus of one of the synergids. gametophyte. Sometimes they dis- —CALDWELL. Fie. 179. One end of the embryo-sac in wake-robin (77rillium). showing endosperm (shaded cells) in which a young embryo is imbedded.—After ATKINSON. 208 PLANT STRUCTURES appear very soon after they are formed; but sometimes they become very active and even divide and form a con- siderable amount of tissue, aiding the endosperm in nour- ishing the young embryo. 114. Development of embryo.—While the endosperm is forming, the oospore has germinated and the sporophyte embryo is developing (Fig. 180). Usually a suspensor, more or less distinct, but never so prominent as in Gymnosperms, is formed; at the end of it the embryo is developed (Fig. 181), which, when completed, is more or less surrounded by nourish- ing endosperm (Fig. 183). The two groups of Angio- sperms differ widely in the struc- ture of the embryo. In Mono- cotyledons the axis of the em- bryo develops the root-tip at one end and the ‘seed-leaf ” (coty- ledon) at the other, the stem-tip arising from the side of the axis as a lateral member (Fig. 182). re nm coed ammo of This relation of orgs recall ing in the upper right enda the embryo of Jsoetes (see § 90). young embryo, in the other Naturally there can be but one end the antipodal cells cut off s by a partition, and seatterea COtyledon under such cireum- through the sac a few free en- stances, and the group has been Seren aptiatee Monocotyledons. In Dicotyledons the axis of the embryo develops the root-tip at one end and the stem- tip at the other, the cotyledons (usually two) appearing as a pair of opposite lateral members on either side of the stem-tip (Fig. 181). This recalls the relation of parts in the embryo of Se/uyinella (see § 89). As the cotyledons are lateral members their number may vary. In Gymno- sperms, whose embryos are of this type, there are often SPERMATOPHYTES: ANGIOSPERMS 209 several cotyledons in a cycle (Fig. 154); and in Dicotyle- dons there may be one or three cotyledons; but as a pair of opposite cotyledons is almost without exception in the group, it is named Dicotyledons. The axis of the embryo between the root-tip and the cotyledons is called the hypocotyl (Figs. 154, 193,194), which Fie. 181. Development of embryo of shepherd's purse (Capsella), a Dicotyledon: beginning with J, the youngest stage, and following the sequence to VJ, the old- est stage, v represents the suspensor, ¢ the cotyledons, s the stem-tip, w the root, h the root-cap. Note the root-tip at one end of the axis and the stem-tip at the other between the cotyledons.—After HANSTEIN. means ‘‘ under the cotyledon,” a region which shows pecul- iar activity in connection with the escape of the embryo from the seed. Formerly it was called either cawlicle or radicle. In Dicotyledons the stem-tip between the coty- 910 PLANT STRUCTURES ledons often organizes the rudiments of subsequent leaves, forming a little bud which is called the plumule. Embryos differ much as to com- pleteness of their development within the seed. In some plants, especially those which are parasitic or sapro- phytic, the embryo is merely a small mass of cells, without any organiza- tion of root, stem, or leaf. In many cases the embryo becomes highly de- veloped, the endosperm being used up and the cotyledons stuffed with food material, the plumule contain- ing several well-organized young leaves, and the embryo completely filling the seed cavity. The com- mon bean is a good illustration of this last case, the whole seed within Fie. 188. Young embryo of the integument consisting of the two Water plantain (Alisma@),€ Jayoe, fleshy cotyledons, between Monocotyledon, the root a c being organized at one Which lie the hypocotyl and a plu- end (next the suspensor), mule of several leaves. atthe other and thestem, 115. The seed,— As in Gymno- tip arising from a lateral sperms, while the processes above notch (#).— After HAN” deseribed are taking place within the ovule, the integument or integu- ments are becoming transformed into the testa (Fig. 183). When this hard coat is fully developed, the activities within cease, and the whole structure passes into that con- dition of suspended animation which is so little under- stood, and which may continue for a long time. The testa is variously developed in seeds, sometimes being smooth and glistening, sometimes pitted, sometimes rough with warts or ridges. Sometimes prominent append- ages are produced which assist in seed-dispersal, as the wings in Catulpa or Bignonia (Fig. 184), or the tufts of SPERMATOPHYTES; ANGIOSPERMS O11 Fig. 183. The two figures to the left are seeds of violet, one showing the black, hard testa, the other being sectioned and showing testa, endosperm, and imbedded embryo; the figure to the right is a section of a pepper fruit (Piper), showing modified ovary wall (pc), seed testa (sc), nucellus tissue (py), endosperm (en), and embryo (em).—After ATKINSON. hair on the seeds of milkweed, cotton, or fireweed (Fig. 185). For a fuller account of the methods of seed-dispersal see Plant Relations, Chapter VI. Fie. 184. A winged seed of Bignonia.—After STRASBURGER. 116. The fruit.—The effect of fertilization is felt beyond the boundaries of the ovule, which forms the seed. The ovary is also involved, and becomes more or less modified. It enlarges more or less, sometimes becoming remarkably enlarged. It also changes in structure, often becoming hard or parchment-like. In case it contains several or numerous seeds, it is organized to open in some way and discharge them, as in the ordinary pods and capsules (Fig. 185). In case there is but one seed, the modified ovary 212 ¥ Ze Yj = Fig. 185. A pod of fireweed (EHpilobium) opening and exposing its plumed seeds which are transported by the wind.-—After Brau. PLANT STRUCTURES wall may invest it as closely as another integument, and a seed-like fruit is the result—a fruit which never opens and is practically a seed. Such a fruit is known as an akene, and is very characteristic of the greatest Angiosperm family, the Composite, to which sunflowers, asters, golden- rods, daisies, thistles, dandelions, ete., belong. Dry fruits which do not open to discharge the seed often bear appendages to aid in dispersal by wind (Figs. 186, 187), or by animals (Fig. 188). Capsules, pods, and akenes are said to be dry fruits, but in many cases fruits ripen fleshy. In the peach, plum, cherry, and all ordinary ‘‘ stone fruits,” the modified ovary wall or- ganizes two layers, the inner being very hard, forming the ‘‘ stone,” the outer being pulpy (Fig. 189), or vari- ously modified (Fig. 190). In the true berries, as the grape, currant, tomato, etc., the whole ovary becomes a thin-skinned pulpy mass in which the seeds are imbedded. In some cases the effect of ferti- lization in chang- ing structure is felt beyond the ovary. Intheap- « / ple, pear, quince, and such fruits, the pulpy part is the modified calyx (one of the Fie. 186. Winged fruit of maple.—After KERNER, SPERM ATOPHYTES: ANGIOSPERMS 913 floral leaves), the ovary and its contained seeds being repre- sented by the “core.” In other cases, the end of the stem bearing the ovaries (receptacle) becomes enlarged and pulpy, as in the strawberry (Fig. 191). This effect some- times involves even more than the parts of a single flower, a whole flower-cluster, with its axis and bracts, becoming an enlarged pulpy mass, as in the pineapple (Fig. 192). The term “fruit,” therefore, Fig. 188. An akene of beg- gar ticks, showing the two barbed appendages which lay hold of animals.—Af- ter BEAL. 32 Fig. 187. A ripe dandelion head, showing the mass of plumes, a few seed-like fruits (akenes) with their plumes still attached to the receptacle, and two fallen off.—After KERNER. Fie. 189. To the left a section of a peach (fruit), showing pulp and stone formed from ovary wall, and the contained seed (kernel); to the right the fruit of almond, which ripens dry.—After Gray. 214 PLANT STRUCTURES is a very indefinite one, so far as the structures it includes are concerned. It is simply an effect which follows fer- tilization, and involves more or less of the structures adja- Fie. 190. Fruit of nutmeg (Iyristica): A, section of fruit, showing seed within the heavy wall; B, section of seed, showing peculiar convoluted and hard endosperm (m) in which an embryo (7) is imbedded.—After BERG and ScuMiptT. cent to the seeds. As has been seen, this effect may extend only to the ovary wall, or it may include the calyx, or it Fie, 191. Fruit of straw- berry, showing the per- sistent calyx, and the en- Jarged pulpy receptacle in which numerous sim- ple and dry fruits (a- kenes) are imbedded.— After BAILEY. lodgment. If the may be specially directed toward the receptacle, or it may embrace a whole flower-cluster. It is what is called a physiological effect rather than a defi- nite morphological structure. 117. Germination of the seed.—lIt has been pointed out (§ 103) that the so-called “ germination of the seed” is not true germination like that of spores. It is the awakening and es- cape of the young sporophyte, which has long before passed through its germination stage. By various devices seeds are sepa- rated from the parent plant, are dis- persed more or less widely, and find lodgment is suitable, there are many devices for burial, such as twisting stalks and awns, bur- SPERMATOPHYTES: ANGIOSPERMS 915 rowing animals, etc. The period of rest may be long or short, but sooner or later, under the influence of moisture, suitable temperature, and oxygen the quiescent seed begins to show signs of life. The sporophyte within begins to grow, and the seed coat is broken or penetrated through some thin spot or Fig. 192, Pineapple: 4, the cluster of fruits forming the so-called ‘‘fruit”; B, single flower, showing small calyx and more prominent corolla; (, section of flower, showing the floral organs arising above the ovary (epigynous).—4, B after Koc; C after LE Maovut and DECAISNE. opening. The root-tip emerges first, is protruded still farther by the rapid elongation of the hypocotyl, soon curves toward the earth, penetrates the soil, and sending out rootlets, becomes anchored. After anchorage in the 216 PLANT STRUCTURES soil, the hypocotyl again rapidly elongates and develops a strong arch, one of whose limbs is anchored, and the other is pulling upon the cotyledons (Fig. 193). This pull finally frees the cotyledons, the hypocotyl straightens, the cotyle- Fie. 193. Germination of the garden bean, showing the arch of the hypocotyl] above ground, its pull on the seed to extricate the cotyledons and plumule, and the final straightening of the stem and expansion of the young leaves.—After ATKINSON. dons are spread out to the air and light, and the young sporophyte has become independent (Fig. 194). In the grain of corn and other cereals, so often used in the laboratory as typical Monocotyledons, but really excep- tional ones, the embryo escapes easily, as it is placed on one side of the seed near the surface. The hypocotyl and stem split the thin covering, and the much-modified cotyle- don is left within the grain to absorb nourishment. In some cases the cotyledons do not escape from the seed, either being distorted with food storage (oak, buck- eye, etc.), or being retained to absorb nourishment from the endosperm (palms, grasses, etc.). In such cases the stem-tip is liberated by the elongation of the petioles of the SPERMATOPHYTES: ANGIOSPERMS O17 cotyledons, and the seed coat containing the cotyledons remains like a lateral appendage upon the straightened axis. It is also to be observed in many cases that the young root system, after gripping the soil, contracts, drawing the young plant deeper into the ground. 118. Summary from Angio- sperms.—At the beginning of this chapter (§ 107) the characters of the Gymnosperms were summar- ized which distinguished them from Angiosperms, whose con- trasting characters may be stated as follows: (1) The microspore (pollen- grain), chiefly by insect pollina- tion, is brought into contact with the stigma, which is a receptive region on the surface of the car- pel, and there develops the pollen- tube, which penetrates the style to reach the ovary cavity which contains the ovules (megasporan- gia). The impossibility of con- tact between pollen and ovule im- plies inclosed ovules and hence seeds, and therefore the name “« Angiosperm.” (2) The female gametophyte is but slightly developed before fertilization, the egg appearing very early. Fic. 194. Seedling of hazel ( Car- pinus), showing primary root (iw) bearing rootlets (sw) upon which are numerous root hairs (r), hypocotyl (%), cotyledons (¢), young stem (e), and first (/) and second (/) true leaves.—After Scumm- PER. (3) The female gametophyte produces no archegonia, but a single naked egg. CHAPTER AIII THE FLOWER 119. General characters——In general the flower may be regarded as a modified branch of the sporophyte stem bear- ing sporophylls and usually floral leaves. Its representa- tive among the Pteridophytes and Gymnosperms is the stro- bilus, which has sporophylls but not floral leaves. Among Angiosperms it begins in a simple and somewhat indefinite way, gradually becomes more complex and modified, until it appears as.an elaborate structure very efficient for its purpose. This evolution of the flower has proceeded along many lines, and has resulted in endless diversity of structure. These diversities are largely used in the classification of Angiosperms, as it is supposed that near relatives are indi- cated by similar floral structures, as well as by other fea- tures. The significance of these diversities is supposed to be connected with securing proper pollination, chiefly by insects, and favorable seed distribution. Although the evolution of flowers has proceeded along several lines simultaneously, now one feature and now another being emphasized, it will be clearer to trace some of the important lines separately. 120. Floral leaves.—In the simplest flowers floral leaves do not appear, and the flower is represented only by the sporophylls. Both kinds of sporophylls may be associated, in which case the flower is said to be perfect (Fig. 195); or they may not both occur in the same flower, in which case one flower is staminate and the other pistillute (Fig. 196). 218 THE FLOWER 919 When the floral leaves first appear in connection with the sporophylls they are inconspicuous, scale-like bodies. In higher forms they become more prominent and inclose Fie. 196. Naked flowers of dif- ferent willows (Salix), each from the axil of a bract: a, 6, ¢, staminate flowers ; d, e, f, pistillate flowers, the pistil composed of two car- pels (syncarpous). — After WARMING. Fic. 195. Lizard’s tail(Saururus): A, tipof branch pPy¢g, 197, Flower of calamus bearing leaves and elongated cluster of flowers; (Acorus), showing simple B, a single naked flower from A, showing sta- perianth, stamens, and syn- mens and four spreading and stigmatic styles; carpous pistil: a hypogynous C, flower from another species, showing sub- flower without differentiation tending bract, absence of floral leaves, seven of calyx and corolla.—After stamens, and a syncarpous pistil; the flowers . Byer. naked and perfect.—After ENGLER. Fie. 199. Common flax (Linum): 1. entire flower, showing calyx and corolla; B, floral leaves re- moved, showing stamens and syncarpous p‘stil; @, a mature Fie. 198, Flowers of elm (Ulmus): A, branch capsule splitting open. — After hearing clusters of flowers and scaly buds ; ScHIMPER. B, single flower, showing simple perianth and stamens, being a stamirate flower; (', flower showing perianth, stamens. and the two divergent styles stigmatic on inner surface, being a perfect flower; JD, section through perfect flower, showing peri- anth, stamens, and pistil with two loculi each with a single ovnle —After ENGLER. Fie. 200. A flower of peony, showing the four sects of floral organs: k, the sepals, to- gether called the calyx; cv, the petals, together called the corolla; a, the numerous stamens; g, the two carpels, which contain the ovules.—After STRASBURGER. THE FLOWER 991 the young sporophylls, but they are all alike, forming what is called the perianth (Figs. 197, 198). In still higher forms the perianth differentiates, the inner floral leaves become more delicate in texture, larger and generally brightly colored (Fig. 199, 1). The outer set may remain scale-like, or become like small foliage leaves. When the dif- ferentiation of the peri- anth is distinct, the outer set of floral leaves is called the calyz, each leaf being a sepal; the inner set is the corolla, each leaf being a petal (Fig. 200). Sometimes, as in the lily, all the floral leaves become uniformly large and brightly colored, in which case the term perianth is retained (Fig. 201). In other cases, the calyx may be the large and colored set, but whenever there is a clear distinction between sets, the outer is the calyx, the inner the corolla. Both floral sets may not appear, and it has become the custom to regard the missing set Fie. 201.—An easter-lily. a Monocotyledon, as the corolla, such showing perianth (a), stamens (4), stigma (c), i . flower bud (d@), and a carpel after the peri- o flowers being called anth has fallen (7), with its knob-like stigma, ape talou 8, meaning long style, and slender ovary.—CALDWELL. 222, PLANT STRUCTURES “without petals.” It is not always possible to tell whether a flower is apetalous—that is, whether it has lost a floral set which it once had—or is simply one whose perianth has not yet differentiated, in which case it would be a ‘‘ primi- tive type.” The line of evolution, therefore, extends from flowers without floral leaves, or naked flowers, to those with a dis- tinctly differentiated calyx and corolla. 121. Spiral to cyclic flowers.—In the simplest flowers the sporophylls and floral leaves (if any) are distributed about an elongated axis in a spiral, like a succession of leaves. That part of the axis which bears the floral organs is for convenience called the receptacle (Fig. 202). As the recep- Fie. 202. A buttercup (Ranwneulus): a, complete flower, showing sepals, petals, sta- mens, and head of numerous carpels on a large receptacle; 6, section showing relation of parts; a hypogynous, polypetalous, apocarpous, actinomorphic flower. —After BarLion. tacle is elongated and capable of continued growth, an in- definite number of each floral organ may appear, especially of the sporopbylls. With the spiral arrangement, there- fore, there is no definiteness in the number of floral organs ; there may be one or very many floral leaves, or stamens, or carpels. The spiral arrangement and indefinite numbers are features of the ordinary strobilus, and therefore such flowers are regarded as more primitive than the others. In higher forms the receptacle becomes shorter, the spiral more closely coiled, until finally the sets of organs THE FLOWER 2923 appear to be thrown into rosettes or cycles. This change does not necessarily affect all the parts simultaneously. For example, in the common buttercup the sepals and petals are nearly in cycles, while the carpels are spirally arranged and indefinitely numerous on the head-lke recep- tacle (Fig. 202). On the other hand, in the common water- IM Fie. 203. Flower of water-lily (Vymphea), showing numerous petals and stamens.— After CasParRy. lily the petals and stamens are spiral, and indefinitely re- peated, while the sepals and carpels are approximately cyclic (Fig. 203). Finally, in the highest forms, all the floral organs are in definite cycles, and there is no indefinite repetition of any part. All through this evolution from the spiral to the cyclic arrangement there is constantly appearing a tend- ency to ‘‘settle down” to certain definite numbers. When the complete cyclic arrangement is finally established these numbers are established, and they are characteristic of great groups. In cyclic Monocotyledons there are nearly always just three organs in each cycle, forming what is called a ¢rimerous flower (Fig. 204) ; while in cyclic Dicot- 994 PLANT STRUCTURES 4 yledons the number five prevails, but often four appears, forming pentumerous or tetramerous flowers (Fig. 199). This does not mean that there are necessarily just three, four, or five of each organ in the flower, for there may be two or more cycles of some one organ. For example, in the common lily there are six floral leaves in two sets, six sta- mens in two sets, and three carpels (Fig. 204). In the cyclic flowers it is also to be noted that each set alternates with the next set outside (Fig. 204). The petals are not directly opposite the se- fo pals, but are opposite the spaces between sepals; the stamens in OS turn alternate with the petals; if (o =) there is a second set of stamens, Be) 2 it alternates with the outer set, % and so on. If two adjacent sets are found opposing one another, it is usually due to the fact that Fic. 204. Diagram of such a @ Set between has disappeared. flower as the lily, showingre- Foy example, if a set of stamens lation of parts: uppermost . : . oraan is the bract intheaxil 18 opposite the set of petals, either of which the flower occurs; an outer stamen set or an inner black dot below indicates po- : sition of stem ; floral parts in petal set has disappeared. threes and in five alternating This line of evolution, there- cyeles (two stamen sets), being — fore, extends from flowers whose a trimerous, pentacyclic flow- 2 ‘ cr.—After SCHIMPER. parts are spirally arranged upon an elongated receptacle and in- definite in number, to those whose parts are in cycles and definite in number. 122. Hypogynous to epigynous flowers—In the simpler flowers the sepals, petals, and stamens arise from beneath the ovary (Figs. 197, 202, 205, 7). As in such cases the ovary or ovaries may be seen distinctly above the origin (insertion) of the other parts, such a flower is often said to have a ‘‘ superior ovary.” The more usual term, however, is hypogynous, meaning in effect “‘ under the ovary,” refer- THE FLOWER lo 25 ring to the fact that the insertion of the other parts is under the ovary. Hypogyny is very largely displaved among flowers, but there is to be observed a tendency in some to carry the insertion of the outer parts higher up. When the outer parts arise from the rim of an urn-like outgrowth from the Fiz, 205. Flowers of Rose family: 1, a hypogynous flower of Pofentilia, sepals. petals, and stamens arising from beneath the head of carpels; 2, a perigynous flower of Alchemilia. sepals. petals, and stamens arising from rim of urn-like pro- longation of the receptacle. which surrounds the carpel; 3. an epizynons flower of the common apple, in which all the parts seem to arise from the top of the ovary, two of whose loculi are seen.—After FockKE. receptacle, which surrounds the pistil or pistils, the flower is said to be perigynous (Figs. 205, 2, 206), meaning * around the pistil.” Finally, the insertion is carried above the ovary. and sepals. petals. and stamens seem to arise from the top of the ovary (Fig. 205, 2), such a flower being epigynovs. the outer parts appearing “‘upon the ovary.” In such a case the ovary does not appear within the flower, but below it (Figs. 205, 252, 261), and the flower is often said to have an ‘* inferior ovary.” 123. Apocarpous to syncarpous flowers——In the simpler flowers the carpels are entirely distinct, each carpel organ- 926 PLANT STRUCTURES izing a simple pistil, a single flower containing as many pistils as there are carpels, as in the buttercups (Figs. 200, 202). Such a flower is said to be apocarpous, meaning “carpels separate.” There is a very strong tendency, Fie. 206. Sweet-scented shrub (Calycanthus): A, tip of branch bearing flowers; B, section through flower, showing numerous floral leaves, stamens, and carpels, and also the development of the receptacle about the carpels, making a perigynous flower.—After THIEBAULT. however, for the carpels of a flower to organize together and form a single compound pistil. In such a flower there may be several carpels, but they all appear as one organ (Figs. 195, C, 197, 198, D, 199, B), and the flower is said to be syncarpous, Meaning ‘‘ carpels together.” 124. Polypetalous to sympetalous flowers—The tendency for parts of the same set to coalesce is not confined to the carpels. Sepals often coalesce (Fig. 208), and sometimes stamens, but the coalescence of petals seems to be more important. Among the lower forms the petals are entirely separated (Figs. 109, .f, 202, 203, 207), a condition which THE FLOWER has received a variety of names, but probably the most common is poly- petalous, meaning “petals many,” although elewtheropetalous, meaning ‘petals free,” is much more to the point. In the highest Angiosperms, how- ever, the petals are coalesced, form- ing a more or less tubular organ (Figs. 208-210). Such flowers are said to be sympetalous, meaning “petals united.” The words gamo- petalous and monopetalous are also Fic, 207. Flower of straw- berry, showing sepals, pet- als, numerous stamens, and head of carpels; the flower is actinomorphic, hypogynous, and with no coalescence of parts.—Af- ter BaILEY. much used, but all three words refer to the same condition of the flower. Often the sympetalous corolla is differenti- Fie. 208. A flower of the tobacco plant: a, a complete flower, showing the calyx with its sepals blended below, the funnelform corolla made up of united petals, and the stamens just showing at the month of the corolla tube; 5. a corolla tube split open and showing the five stamens attached to it near the base; c, a syncarpous pistil made up of two carpels, showing ovary, style, and stigma.—After STRASBURGER. 298 PLANT STRUCTURES ated into two regions (Fig. 210, 6), a more or less tubular portion, the ¢wbe, anda more or less flaring portion, the (im. 125. Actinomorphic to zygomorphic flow- ers.—In the simpler flowers all the mem- bers of any one cycle are alike; the petals are all alike, the stamens are all alike, etc. Looking at the center of the flower, all the parts are re- peated about it like the parts of a radi- ate animal. Such a flower is actinomor- Fie 209. Flower of morning-glory (Ipomea), with phic, meaning ra sympetalous corolla split open, showing the five 3 ” : attached stamens, and the superior ovary with diate, and 1S often prominent style and stigma; the flower is hy- called ai ‘“* regular pogynons, sympetalous, and actinomorphic.— » After MBISsSNER. flower. Although the term actinomor- phic strictly applies to all the floral organs, it is especially noteworthy in connection with the corolla, whose changes will be noted. Fie. 210. A group of sympetalous flower forms: @, a flower of harebell, showing a bell-shaped corolla; &, a lower of phlox, showing a tube and spreading limb; ¢, a flower of dead-nettle, showing a zygomorphic two-lipped corolla; d, a flower of toad-flax, showing a two-lipped corolla, and also a spur formed by the base of the corolla; é, a flower of the snapdragon, showiug the two lips of the corolla closed. —After GRay, THE FLOWER 929 In many cases the petals are not all alike, and the radi- ate character, with its similar parts repeated about a cen- ter, is lost. In the common violet, for example, one of the petals develops a spur (Fig. 211); in the sweet pea the petals are remarkably un- like, one being broad and erect, two small- er and drooping downward, and the other two much modi- fied to form together a boat-like structure which incloses the Fie. 211. The pansy (Violu tricolor): A, section showing sepals (/,/’), petals (¢) one of which produces a spur (cs). the flower being zygomor- phic; B, mature fruit (a cap-ule) and persistent calyx (k); C, the three boat-shaped valves of the fruit open, most of the seeds (s) having been discharged.— After Sacus. sporophylls. Such flowers are called zygomorphir, meaning “ yoke-form,” and they are often called * irregular flowers.” When zygomorphic flowers are also sympetalous the corolla is often curiously shaped. A very common form Fig. 212. Flower of a mint (Jutha aquaticas: A, the entire flower. showing calyx of united sepals, unequal petals. stamens, and style with two stigma lobes; B,a corolla split open, showing petals united and the four stamens attached to the tube; the flower is sympetalous and zygomorphic.—After WERMING. 33 230 PLANT STRUCTURES is the dilabiate, or ** two-lipped,” in which two of the petals usually organize to form one lip, and the other three form Fic. 213. Flower of a Labiate (Teucrium), showing the calyx of coalesced sepals, the sympetalous and two-lipped (bilabi- ate) corolla with three petals (middle one largest) in the lower lip and two small ones in the upper, and the stamens and style emerging through a slit on the up- per side of the tube; a sympctalous and zygomorphic flower.—After Briquert. the other lip (Figs. 210, ¢, d, é, 212, 213). The two lips may be nearly equal, the upper may stand high or overarch the lower, the lower may project more or less conspicuously, etc. 126. Inflorescence— Very often flowers are soli- tary, either on the end of a stem or branch (Figs. 231, 236), or in the axil of a leaf (Fig. 258). But such cases grade insensibly into others where a definite region of the plant is set aside to produce flowers (Figs. 253, 260). Such a region forms what is called the znflo- rescence. The various ways in which flowers are arranged in an inflorescence have received technical names, but they do not enter into our purpose here. They are simply dif- ferent ways in which plants seek to display their flowers so as to favor pollination and seed distribution. There are several tendencies, however, which may be noted. Some groups incline to loose clusters, either elon- gated (Fig. 260) or flat-topped (Fig. 253); others prefer large and often solitary flowers (Fig. 258) to a cluster of smaller ones; but in the highest groups there is a distinct tendency to reduce the size of the flowers, increase their number, and mass them into a compact cluster. This ten- dency reaches its highest expression in the greatest family of the Angiosperms, the Composite, of which the sunflower or dandelion can be taken as an illustration (Figs. 261, 262), in which numerous small flowers are closely packed together in a compact cluster which resembles a single large flower. It does not follow that all very compact inflorescences in- THE FLOWER 231 dicate plants of high rank, for the cat-tail flag (Fig. 221) and many grasses have very compact inflorescences, and they are supposed to be plants of low rank. It is to be noted, however, that the very highest groups have settled upon this as the best type of inflorescence. 127. Summary.—In tracing the evolution of flowers, therefore, the following tendencies become evident: (1) from naked flowers to those with distinct calyx and corolla ; (2) from spiral arrangement and indefinite numbers to cyclic arrangement and definite numbers; (3) from hypogynous to epigynous flowers ; (4) from apocarpous to syncarpous pistils ; (5) from polypetalous to sympetalous corollas ; (6) from actinomorphic or regular to zygomorphic or irregular flowers ; (7) from loose to compact inflorescences. These various lines appear in all stages of advancement in different flowers, so that it would be impossible to deter- mine the relative rank in all cases. However, if a flower is naked, spiral, with indefinite numbers, hypogynous, and apocarpous, it would certainly rank very low. On the con- trary, the flowers of the Composite have calyx and corolla, are cyclic, epigynous, syncarpous, sympetalous, often zygo- morphic, and are in a remarkably compact inflorescence, indicating the highest possible combination of characters. 128. Flowers and insects.— The adaptations between flowers and insects, by which the former secure pollination and the latter food, are endless. Many Angiosperm flowers, especially those of the lower groups, are still anemophilous, as are the Gymnosperms, but most of them, by the presence of color, odor, and nectar, indicate an adaptation to the visits of insects. This wonderful chapter in the history of plants will be found discussed, with illustrations, in Plant Relations, Chapter VII. CHAPTER XIV MONOCOTYLEDONS AND DICOTYLEDONS 129. Contrasting characters—The two great groups of Angiosperms are quite distinct, and there is usually no dif- ficulty in recognizing them. The monocotyledons are usually regarded as the older and the simpler forms, and are represented by about twenty thousand species. The Dicotyledons are much more abundant and diversified, con- taining about eighty thousand species, and form the domi- nant vegetation almost everywhere. The chief contrasting characters may be stated as follows: Monocotyledons. — (1) Embryo with terminal cotyledon and lat- eral stem-tip. This character is practically without exception. (2) Vascular bundles of stem scattered (Hig. 214). This means that there is no annual increase in ei the diameter of the woody stems, Fie. 214. Section of stem of : : corn, showing the scatterea @nd no extensive branching, but bundles, indicated by black to this there are some exceptions. dots in cross-section, and by : : lines in longitudinal section, (3) Leat velns forming a closed —From ‘Plant Relations.” system (Fig. 215, figure to left). As a rule there is an evident set of veins which run approximately parallel, and intricately branching between them is a system of minute veinlets not readily seen. ‘The vein system does not end freely in the 282 MONOCOTYLEDONS AND DICOTYLEDONS 933 margin of the leaf, but forms a ‘‘ closed venation,” so that the leaves usually have an even (ev/ire) margin. There are some notable exceptions to this character. (4) Cyclic flowers trim- erous. The ‘“three-parted ” SE 6S plo i i a My 4 ey i i ue i: % "y if ss i Ms i x t SS Snes i y ° = cca Beco pe 6 Fig. 215. Two types of leaf venation: the figure to the left is from Solomon’s seal, a Monocotyledon, and shows the principal veins parallel, the very minute cross veinlets being invisible to the naked eye; that to the right is from a willow, a Dicotyledon, and shows netted veins, the main central vein (midrib) sending out a series of parallel branches, which are connected with one another by a network of veinlets.—After ETTINGSHAUSEN. flowers of cyclic Monocotyledons are quite characteristic, but there are some trimerous Dicotyledons. Dicatyleduns.—(1) Embryo with lateral cotyledons and terminal stem-tip. (2) Vascular bundles of stem forming a hollow cylinder (Fig. 216, w). This means an annual increase in the diam- 934 PLANT STRUCTURES Fig. 216. Section across a young twig of box elder, showing the four stem regions: é, epidermis, represented by the heavy bounding line; ¢, cortex; w, vascular cyl- inder; p, pith. From ‘‘ Plant Relations.” eter of woody stems (Fig. 217, w), and a_ possible increase of the branch system and foliage dis- play each year. (3) Leaf veins form- ing an open system (Fig. 215, figure to right). The network of smaller veinlets between the larger veins is usually very evident, especially on the under surface of the leaf, suggesting the name ‘net-veined” leaves, in contrast to the ‘‘ parallel-veined ” leaves of Mono- cotyledons. this, although the leaf may remain entire, it very commonly be- comes toothed, lobed, and divided in various ways. Two main types of venation may be noted, which influence the form of leaves. In one case a single very prominent vein (77d) runs through the mid- dle of the blade. and is called the midrib. From this all the mi- nor veins arise as branches (Figs. 218, 219), and such a leaf The vein system ends freely in the margin of the leaf, forming an ‘* open venation.” In consequence of Fra. 217. Section across 1 twig of box elder three years old, showing three annual rings, or growth rings, in the vascular cylinder, the radiating lines (m) which cross the vascular region (w) represent the pith rays, the princi- pal ones extending from the pith to the cor- tex (c).—From ‘“‘ Plant Relations.” MONOCOTYLEDONS AND DICOTYLEDONS 93° Or is said to be pinnate or pinnately veined, and inclines to elongated forms. In the other case several ribs of equal prominence enter the blade and diverge through it (Fig. 218). Such a leaf is palmate or palinately veined, and in- clines to broad forms. (4) Cyclic flowers pentamerous or tetramerous. The flowers ‘‘in fives” are greatly in the majority, but some Fic. 218. Leaves showing pinnate and palmate branching; the one to the left is from sumach, that to the right from buckeye.—CALDWELL. very prominent families have flowers “‘in fours.” There are also dicotyledonous families with flowers ‘‘in threes,” and some with flowers ‘‘in twos.” It should be remembered that no one of the above char- acters, unless it be the character of the embryo, should be depended upon absolutely to distinguish these two groups. OB PLANT STRUCTURES It is the combination of characters which determines a group. MonocoTyLEDONS 130. Introductory.—This great group gives evidence of several distinct lines of development, distinguished by what may be called the working out of different ideas. In this way numerous families have resulted—that is, groups of Fie. 219, A leaf of honey locust, to show twice pinnate branching (bipinnate leaf).— CALDWELL. forms which seem to belong together on account of similar structures. This similarity of structure is taken to mean relationship. A family, therefore, is made up of a group of nearly related forms Opinions may differ as to what forms are so nearly related that they deserve to consti- tute a distinct family. SS peculiar pod (le- gume) which has given to the family its technical name Fie. 251. A sensitive-plant (Acacia), showing the Leguminose and flowers with inconspicuous petals and very nu- merous stamens, and the pinnately branched sen- the common name sitive leaves.—After Meyer and ScHuMANN. “ Legumes.” Well-known members of the family are lupine (Lupi- nus), Clover (Trifolium), locust (Robinia), Wistaria, pea (Pisum), bean (Phaseolus), tragacanth (.1s/ragalus), vetch (Vicia), redbud ((ere/s), senna (Cassia), honey-locust ( Gleditschia), indigo (Indigofera), sensitive-plants (Acacia, Mimosa, etc.) (Fig. 251), etc. 266 PLANT STRUCTURES 142. Umbellifers—This is the most highly organized family (Umbellifere) of the Archichlamydex, which may be said to extend from Peppers to Umbellifers. The Le- gumes adopt zygomorphy, but remain hypogynous ; and in some of the Roses epigyny appears; but the Umbellifers with their fifteen hundred species are all distinctly epigy- Fie. 252. The common carrot (Daucus Carota): 4. branch bearing the compound umbels; B, u single epigynous flower, showing inferior ovary, five spreading petals, five stamens alternating with the petals, and the two styles of the bicarpel- lary pistil; (, section of flower, showing relation of parts, and also the minute sepals near the top of the ovary and just beneath the other parts, —After WARMING. nous (Fig. 252, B, (), being one of the very few epigy- nous families among the Archichlamydex. In addition to epigyny, the cyclic arrangement and definite Dicotyl number is established, there being five sepals, five petals, five stamens, and two carpels, the highest known floral MONOCOTYLEDONS AND DICOTYLEDONS 267 formula, and one that appears among the highest Sym- petale. The name of the family is suggested by the character- istic inflorescence, which is also of advanced type. The flowers are reduced in size and massed in flat- topped clusters called Ae umbels (Figs. 252, A, 253). The branches of the clus- ter arise in cycles from the axis like the braces of an umbrella. As a re- sult of the close approxi- mation of the flowers the sepals are much reduced in size and often obsolete (Fig. 252, (). The Umbellifers are mainly perennial herbs of the north temperate re- gions, forming a very dis- tinct family, and contain- ing the following familiar forms: carrot (Daucus) (Fig. 252), parsnip (Pasti- naca), hemlock (Coniun) (Fig. 253), pepper-and- salt (Erigenia), caraway (Carum), fennel (Fente- ulum), coriander (Cori- andrum), celery (Apt- um), parsley (Petroseli- num), etc. Allied to the Umbellifers are the Ara- lias (Araliacee), and the Dogwoods (Cornacee). Fie. 253. Hemlock (Conium), an Umbellifer, showing the umbels, with the principal rays rising from a cycle of bracts (invo- lucre), and each bearing at its summit a secondary umbel with its cycle of second- ary bracts (énvolucel).—After SCHIMPER. 268 PLANT STRUCTURES Sympetale 143. Introductory.—These are the highest and the most recent Dicotyledons. While they contain numerous shrubs and trees in the tropics, they are by no means such a shrub and tree group in the temperate regions as are the Archi- chlamydee. The flowers are constantly cyclic, the num- ber five or four is established, and the corolla is sympeta- lous, the stamens usually being borne upon its tube (Figs. 208, 209, 212). There are two well-defined groups of Sympetale, distin- guished from one another by the number of cycles and the number of carpels in the flower. The group containing the lower forms is pexfacyclic, meaning ‘ cycles five,” there being two sets of stamens. In it also there are five carpels, the floral formula being, Sepals 5, Petals 5, Stamens 5 + 5, Carpels 5. As the carpels are the same in number as the other parts, the flowers are called dsocarpic, meaning * car- pels same.” The group is named either Pentacycl or [so- carpe, and contains about ten families and 4,000 species. The higher groups, containing about forty families and 36,000 species, is fetracyclic, meaning ** cycles four,” and anisocarpic, Meaning *‘carpels not the same,” the floral formula being, Sepals 5, Petals 5, Stamens 5, Carpels 2. The group name, therefore, is Tefrarycle or Anisocurpe. 144. Heaths.—The Heath family (Hricace) and its allies represent about two thousand species. They are mostly shrubs, sometimes trailing, and are displayed chiefly in temperate and arctic or alpine regions, in cold and damp or dry places, often being prominent vegetation in bogs and heaths, to which latter they give name (Fig. 254). The flowers are pentacyclic and isocarpic, as well as mostly hyp- ogynous and actinomorphic. It is interesting to note that some forms are not sympetalous, the petals being distinct, showing a close relationship to the Archichlamydex. One of the marked characteristics of the group is the dehiscence MONOCOTYLEDONS AND DICOTYLEDONS 969 of the pollen-sacs by terminal pores, which are often pro- longed into tubes (Fig. 255). Fie. 254. Characteristic heath plants: 4, B. (, Lyonia, showing sympetalous flowers and single style from the lobed syncarpous ovary; D, two forms of Cassiope, showing trailing habit, small overlapping leaves, and sympetalous flowers, but in the smaller form the petals are almost distinct.—After DRUDE. Common representatives of the family are as follows: huckleberry ((aylussacia), cranberry and blueberry ( Vuc- cinium), bearberry (.Aretostaphylos), trailing arbutus (£p/- 270 PLANT STRUCTURES gea), wintergreen (Gaultheria), heather (Calluna), moun- tain laurel (Aalmia), Azalea, Rhododendron (Fig. 256), Indian pipe (Monotropa), etc. Fig, 255. Flowers of heath plants (#rica), showing complete flowers (4), the sta- mens with ‘‘ two-horned”’ anthers which discharge pollen throngh terminal pores, and the lobed syncarpous ovary with single style and prominent terminal stigma (B, C, D).—After DruvDeE. 145. Convolvulus forms.—The well-known morning-glory (Jpomea) (Fig. 209) may be taken as a type of the Convol- MOSOCOTYLEDONS AND DICOTYLEDORKS 971 vulus family (Convolvulacee). Allied with it are Polemo- nium and Phlov (Fig. 210, b) (Polemoniacee), the gentians (Gentianacew), and the dog-banes (lpocynacee) (Fig. 257). It is here that the regular sympetalous flower reaches its highest expression in the form of conspicuous tubes, fun- Fie. 256. A cluster of Rhododendron flowers.—After HooKER. nels (Fig. 258), trumpets, etc. The flowers are tetracyclic and anisocarpic, besides being hypogynous and actinomor- phic. These regular tubular forms represent about five thousand species, and contain many of the best-known flowers. 979 PLANT STRUCTURES 146. Labiates—This great family (Zadiate) and its alli- ances represent more than ten thousand species. The con- spicuous feature is the zygomorphic flower, dif- fering in this regard from the Convolvulus forms, which they resemble in being tetraeyclic and ani- socarpic, as well as hypogy- nous. The irregularity consists in organizing the mouth of the sympetalous corolla imto two ‘* lips,” resulting in the /abiate or Fie. 257. A common dogbane (.fpocynum).—From “Field, Forest, and Wayside Flowers.” Fig. 258. The hedge bindweed ( Conro/eudus), showing the twining habit and the con- spicuous funnelform corollas.—From “ Field. Forest, and Wayside Flowers.” O74 PLANT STRUCTURES bilabiate structure (Fig. 210, ¢, d, ¢), and suggesting the name of the dominant family. The upper lip usually con- tains two petals, and the lower three ; the two lips are some- times widely separated, and sometimes in close contact, and differ widely in relative prominence. Associated with zygomorphy in this group is a frequent reduction in the number of stamens, which are often four (Fig. 212) or two. The whole structure is highly special- ized for the visits of insects, and this great zygomorphic alliance holds the same relative position among Sympetale as is held by the zygomorphic Le- gumes among Archi- chlamydee. In the mint family, as the Labiates are often called, there are about two thousand seven hun- dred species, including mint (Mentha) (Fig. 212), dittany (Cunila), hyssop (Hyssopus), mayr- joram (Origanum), Fie. 259. Flowers of dead nettle (Za- Fre. 260. A labiate plant (Zeucrium), show- mium): A, entire bilabiate flower ; ing branch with flower clusters (4), and B, section of flower, showing rela- side view of a few flowers (B), showing tion of parts.—After Warmina, their bilabiate character.—After Briqugt, MONOCOTYLEDONS AND DICOTYLEDONS 975 thyme (Thymus), balm (Jelissa), sage (Salvia), catnip (-Vepeta), skullcap (Scutelluria), horehound (Murrubium), lavender (Lavandula), rosemary (Rosmarinus), dead nettle (Lamium) (Fig. 259), Teuertum (Figs. 218, 260), etc., a remarkable series of aromatic forms. Allied is the Nightshade family (Solanacee), with fif- teen hundred species, containing such common forms as the nightshades and potato (So/anwm), tomato (Lycoper- sicum), tobacco (.Vicotiana) (Fig. 208), etc., in which the corolla is actinomorphic or nearly so; also the great Fig- wort family (Scrophulariacee), with two thousand species, represented by mullein ( Verbdascum), snapdragon (intir- rhinum) (Fig. 210, ¢), toad-flax (Linaria) (Fig. 210, d), Pentstemon, speedwell (Veronica), Gerardia, painted cup (Castilleta), etc.; also the Verbena family (Verdenacee), with over seven hundred species; and the two hundred plantains (Pluntaginucee), etc. 147. Composites—This greatest and ranking family (Composite) of Angiosperms is estimated to contain at least twelve thousand species, containing more than one seventh of all known Dicotyledons and more than one tenth of all Seed-plants. Not only is it the greatest family, but it is the youngest. Composites are distributed everywhere, but are most numerous in temperate regions, and are mostly herbs. The name of the family suggests the most conspicuous feature—namely, the remarkably complete organization of the numerous small flowers into a compact head which resembles a single flower, formerly called a ‘‘ compound flower.” Taking the head of an Arnica as a type (Fig. 261), the outermost set of organs consists of more or less leaf-like bracts or scales (‘nxvolucre), which resemble sepals ; within these is a circle of flowers with conspicuous yellow corollas (rays), which are zygomorphic, being split above the tubular base and flattened into a strap-shaped body, and much resembling petals (Fig. 261, 1, 2); within the Fie. 261. Flowers of Arnica? .1, lower part of stem, and upper part bearing a head, in which are seen the conspicuous rays and the disk; D, single ray flower, showing the corolla, tubular at base and strap-shaped above, the two-parted style, the tuft of pappus hairs, and the inferior ovary which develops into a secd-like fruit (akene); Z#. single disk flower, showing tubular corolla with spreading limb, the two-parted style emerging from the top of the stamen tube, the prominent pappus, and the inferior ovary or akene; (', a single stamen,—Aftcr IlorFMAN. 276 MONOCOTYLEDONS AND DICOTYLEDONS OTT ray-flowers is the broad expanse supplied by a very much broadened axis, and known as the disk (Fig. 261, 4), which is closely packed with very numerous small and regular tubular flowers, known as disk-flowers (Fig. 261, e). Fic. 262. The common dandelion ( Tararacvm): 1, two flower stalks; in one the head is closed, showing the double involucre, the inner erect, the outer reflexed, in the other the head open, showing that all the flowers are strap-shaped; 2, a single flower showing inferior ovary, pappus, corolla, stamen tube, and two-parted style; 3, amature akene; 4, a head from which all but one of the akenes have been re- moved, showing the pitted receptacle and the prominent pappus beak.—After STRASBURUER. The division of !abor among the flowers of a single head is plainly marked, and sometimes it becomes quite com- plex. The closely packed flowers have resulted in modity- ing the sepals extremely. Sometimes they disappear en- 36 278 PLANT STRUCTURES tirely ; sometimes they become a tuft of delicate hairs, as in Arnica (Fig. 261, D, #), thistle (Caicus), and dandelion (Taravacum) (Fig. 263), surmounting the seed-like akene and aiding in its transportation through the air ; sometimes they are converted into two or more tooth-like and often Fie. 263. Flowers of dandelion, showing action of style in removing pollen from the stamen tube: 7, style having elongated through the tube and carrying pollen; 2, style branches beginning to recurve; 3, style branches completely recurved.— From ‘ Field, Forest, and Wayside Flowers.” barbed processes arising from the akene, as in tickseed (Coreopsis) and beggar-ticks (Fig. 188) or Spanish needles (Bidens), to lay hold of passing animals ; sometimes they become beautifully plumose bristles, as in the blazing star (Liatris) ; sometimes they simply form a more or less con- spicuous cup or set of scales crowning the akene. In all of these modifications the calyx is called pappus. The stamens within the corolla are organized into a tube by their coalescent anthers (Fig. 263), and discharge their pollen within, which is carried to the surface of the MONOCOTYLEDONS AND DICOTYLEDONS 979 head and exposed by the swab-like rising of the style (Fig. 263). The head is thus smeared with pollen, and visiting insects can not fail to distribute it over the head or carry it to some other head. In the dandelion and its allies the flowers of the disk are like the ray-flowers, the corolla being zygomorphic and strap-shaped (Figs. 262, 263). The combination of characters is sympetalous, tetracyc- lic, and anisocarpic flowers, which are epigynous and often zygomorphic, with stamens organized into a tube and calyx modified into a pappus, and numerous flowers organized into a compact involucrate head in which there is more or less division of labor. There is no group of plants that shows such high organization, and the Composite seem to deserve the distinction of the highest family of the plant kingdom. The well-known forms are too numerous to mention, but among them, in addition to those already mentioned, there are iron-weed (Vernonia), Aster, daisy (ellis), goldenrod (Solidago), rosin-weed and compass-plant (Si/ph- tum), sunflower (Helianthus), Chrysanthemum, ragweed (Ambrosia), cocklebur (.Yanthium), ox-eye daisy (Leucan- themum), tansy (Lanacetum), wormwood and sage-brush (Artemisia), lettuce (Lactuca), etc. CHAPTER XV DIFFERENTIATION OF TISSUES 148. Introductory— Among the simplest Thallophytes the cells forming the body are practically all alike, both as to form and work. What one cell does all do, and there is very little dependence of cells upon one another. As plant bodies become larger this condition of things can not continue, as all of the cells can not be put into the same relations. In such a body certain cells can be related to the external food supply only through other cells, and the body becomes differentiated. In fact, the relating of cells to one another and to the external food-supply makes large bodies possible. The first differentiation of the plant body is that which separates nutritive cells from reproductive cells, and this is accomplished quite completely among the Thallophytes. The differentiation of the tissues of the nutritive body, however, is that which specially concerns us in this chapter. A tissue is an aggregation of similar cells doing similar work. Among the Thallophytes the nutritive body is prac- tically one tissue, although in some of the larger Thallo- phytes the outer and the inner cells differ somewhat. This primitive tissue is composed of cells with thin walls and active protoplasm, and is called parenchyma, meaning “parent tissue.” Among the Bryophytes, in the leafy gametophore and in the sporogonium, there is often developed considerable dissimilarity among the cells forming the nutritive body, but the cells may all still be regarded as parenchyma. It 280 DIFFERENTIATION OF TISSUES 981 isin the sporophyte of the Pteridophytes and Spermato- phytes that this differentiation of tissues becomes extreme, and tissues are organized which differ decidedly from parenchyma. This differentiation means division of labor, and the more highly organized the body the more tissues there are. All the other tissues are derived from parenchyma, and as the work of nutrition and of reproduction is always retained by the parenchyma cells, the derived tissues are for mechanical rather than for vital purposes. There is a long list of these derived and me- chanical tissues, some of them being of general’ occurrence, and others more restricted, and there is every gradation 7 between them and the gre. 264. Parenchyma and sclerenchyma from parenchyma from which the pa of Pteris, in cross-section.—CHAmM- they have come. We ~~ shall note only a few which are distinctly differentiated and which are common to all vascular plants. 149. Parenchyma,—The parenchyma of the vascular plants is typically made up of cells which have thin walls and whose three dimensions are approximately equal (Figs. 264, 265). though sometimes they are elongated. Until abandoned, such cells contain very active protoplasm, and it is in them that nutritive work and cell division are carried on. So long as these cells retain the power of cell division the tissue is called meristem, or it is said to be meristematic, from a Greek word meaning ‘to divide.” When the cells stop dividing, the tissue is said to be permanent. The growing points of organs, as stems, roots, and leaves, are composed of parenchyma which is meristematic (Figs. 266, 274), and meristem occurs wherever growth is going on. 2982 PLANT STRUCTURES 150. Mestome and stereome——When the plant body be- comes complex a conductive system is necessary, so that the different regions of the body may be put into communi- cation. The material absorbed by the roots must be carried to the leaves, and the food manu- factured in the leaves must be carried to regions of growth and storage. This business of transportation is provided for by the specially organized ves- sels referred to in preceding chapters, and all conducting tis- sue, of whatever kind. is spoken of collectively as mestome. If a complex body is to main- tain its form, and especially if it is to stand upright and be- come large, it must develop structures rigid enough to fur- nish mechanical support. All the tissues which serve this pur- pose are collectively known as Fie. 265. Same tissues as in pre- stereome. ceding figure, in longitudinal sec- The sporophyte body of meic—CHaumetus. Pteridophytes and Spermato- phytes, therefore, is mostly made up of living and working parenchyma, which is traversed by mechanical mestome and stereome. 151. Dicotyl and Conifer stems.—The stems of these two groups are so nearly alike in general plan that they may be considered together. In fact, the resemblances were once thought to be so important that these two groups were put together and kept distinct from Monocotyledons ; but this was before the gametophyte structures were known to bear very different testimony. DIFFERENTIATION OF TISSUES 283 At the apex of the growing stem there is a group of active meristem cells, from which all the tissues are de- rived (Fig. 266). This group is known as the apical group. Below the apical group the tissues and regions of the stem begin to appear, and still farther down they become dis- tinctly differentiated, passing into permanent tissue, the apical group by its divisions continually adding to them and increasing the stem in length. Just behind the apical group, the cells begin to give the appearance of being organized into three great embryonic re- gions, the cells still remaining meristem- Fic. 266. Section through growing point of stem of < : Hippuris : below the growing point, composed atic (Fig. 266). At of a uniform meristem tissue, the three embry- the surface there is a onic regions are outlined, showing the dermato- “ gen (da, d), the central plerome (,/, p), and be- single layer of cells tween them the periblem.—After DE Bary. distinct from those within, known as the dermatogen, or ‘“ skin-producer,” as farther down, where it becomes permanent tissue, it is the epidermis. In the center of the embryonic region there is organized a solid cylinder of cells, distinct from those around it, and called the plerome, meaning “that which fills up.” Farther down, where the plerome passes into permanent tissue, it is called the central cylinder or stele (‘‘column”). Between the plerome and dermatogen is a tissue region called the periblem, meaning “that which is put around,” and when it becomes permanent tissue it is called the cor/ex, meaning “ bark” or “rind.” Putting these facts together, the general statement is that at the apex there is the apical group of meristem cells ; 84 PLANT STRUCTURES below them are the three embryonic regions, dermatogen, periblem, and plerome; and farther below these three regions pass into permanent tissue, organizing the epider- mis, cortex, and stele. The three embryonic regions are usually not so distinct in the Conifer stem as in the Dico- tyl stem, but both stems have epidermis, cortex, and stele. Epidermis.—The epidermis is a protective layer, whose cells do not become so much modified but that they may be regarded as parenchyma. It gives rise also to super- ficial parts, as hairs, etc. In the case of trees, the epidermis does not usually keep up with the increasing diameter, and disappears. This puts the work of protection upon the cortex, which organizes a superficial tissue called cork, a prominent part of the structure known as bark. Cortee.—The cortex is characterized by containing much active parenchyma, or primitive tissue, being the chief seat of the life activities of the stem. Its superficial cells, at least, contain chlorophyll and do chlorophyll work, while its deeper cells are usually temporary storage places for food. The cortex is also char- acterized by the development of stereome, or rigid tissues for me- chanical support. The stereome may brace the epidermis, forming the hypodermis ; or it may form bands and strands within the cor- tex; in fact, its amount and ar- rangement differ widely in differ- ent plants. The two principal stereome tis- Fr ee mn ms sues are collenchyma and seleren- mon dock (umes), showing Chyna, meaning *‘ sheath-tissue ” ie ee te and “hard-tissue” respectively. In collenchyma the cells are thick- ened at the angles and have very elastic walls (Fig. 26%), making the tissue well adapted for parts which are growing DIFFERENTIATION OF TISSUES 985 in length. The chief mechanical tissue for parts which have stopped growing in length is sclerenchyma (Figs. 264, 265). The cells are thick-walled, and usually elongated and with tapering ends, including the so-called “ fibers.” A, cross-section; B, longitudinal section; the letters in both referring to the same structures; J/, pith; XY, xylem, containing spiral (s, s’) and pitted (¢, ¢’) vessels; ¢, cambium; P, phloem, containing sieve vessels (sb); 6, a mass of bast fibers or sclerenchyma; ic, pith rays between the bundles; e, the bundle sheath; 7, cor- tex.—After VINES. Stele.—The characteristic feature of the stele or central cylinder is the development of the mestome or vascular 286 PLANT STRUCTURES tissues, of which there are two prominent kinds. The tracheary vessels are for water conduction, and are cells with heavy walls and usually large diameter (Fig. 268). The thickening of the walls is not uniform, giving them a very characteristic appearance, the thickening taking the form of spiral bands, rings, or reticulations (Fig. 268, B). Often the reticulation has such close meshes that the cell wall has the appearance of being covered with thin spots, and such cells are called ‘‘ pitted vessels.” The vessels with spirals and rings are usually much smaller in diameter than the pitted ones. The true tracheary cells are more or less elongated and without tapering ends, fitting end to end and forming a continuous longitudinal series, suggesting a trachea, and hence the name. In the Conifers there are no true tracheary ceils, as in the Dicotyledons, except a few small spiral vessels which are formed at first in the young stele, but the tracheary tissue is made up of ¢racherds, mean- ing “trachea-like,” differing from truchee or true tracheary vessels in having tapering ends and in not forming a continu- ous series (Fig. 269). The walls of these tracheids are ** pitted” in a way which is characteristic of Gymnosperms, the ‘pits ” appearing as two concentric rings, called “ bordered pits.” Fra. 269. ‘Tracheids from wood of The other prominent mes- pe sng teri evs tome tissue developed in the stele is the steve vessels, for the conduction of organized food, chiefly proteids (Fig. 208). Sieve cells are so named because in their walls special areas are organized which are perforated like the lid of a pepper- DIFFERENTIATION OF TISSUES IST box or a “sieve.” These perforated areas are the szeve- plates, and through them the vessels communicate with one another and with the adjacent tissue. The tracheary and sieve vessels occur in separate strands, the tracheary strand being called .rylem (“ wood”), the sieve strand phloem (“bark”). A xylem and a phloem strand are usually organized together to form a vascular bundle, and it is these fiber-like bundles which are found traversing the stems of all vascular plants and appearing conspicuously as the veins of leaves. Among the Dicotyls and Conifers the vascular bundles appear in the stele in such a way as to outline a hollow cylinder (Fig. 216), the xylem of each bundle being toward the center, the phloem toward the circumference of the stem. The undifferenti- ated parenchyma of the stele which the vascular cylinder incloses is called the pith. In older parts of the stem the pith is often abandoned by the activities of the plant, and either remains as a dead spongy tissue, or disappears en- tirely, leaving a hollow stem. Between the bundles form- ing the evsrulur cylinder there is also undifferentiated parenchyma, and as it seems to extend from the pith out between the bundles like ‘‘rays from the sun,” the rays are called pith rays. Such vascular bundles as described above, in which the xylem and phloem strands are ‘‘ side-by-side ” upon the same radius, are called collatvral (Fig. 270). One of the pecul- iarities of the collateral bundles of Dicotyls and Conifers, however. is that when the two strands of each bundle are organized some meristem is left between them. This means that between the strands the work of forming new cells can goon. Such bundles are said to be open; and the apen collateral bundle is characteristic of the stems of the Dico- tyls and Conifers. The meristem between the xylem and phloem of the open bundle is called cambium (Figs. 268, 270). The cam- bium also extends across the pith rays between the bundles, 288 PLANT STRUCTURES connecting the cambium in the bundles, and thus forming acambium cylinder, which separates the xylem and phloem of the vascular cylinder. This cambium continues the for- > Fig. 270. Cross-section of open collateral vascular bundle from stem of castor-oil plant (Ricinus), showing pith cells (7), xylem containing spiral (2) and pitted (gq) vessels, cambium of bundle (¢) and of pith rays (cb), phloem containing sieve ves- sels (y), three bundles of bast fibers or sclerenchyma (d), the bundle sheath con- taining starch grains, und outside of it parenchyma of the cortex (r),—After Sacits. mation of xylem tissue on the one side and phloem tissue on the other in the bundles, und new parenchyma between the bundles, and so the stem increases in diameter. If the stem lives from year to year the addition made by the cam- bium each season is marked off from that of the previous season, giving rise to the so-called growth rings or annual rings, 80 conspicuous a feature of the cross-section of tree DIFFERENTIATION OF TISSUES 989 trunks (Fig. 217). This continuous addition to the vessels increases the capacity of the stem for conduction, and per- mits the further extension of branches and a larger display of leaves. The annual additions to the xylem are added to the in- creasing mass of wood. The older portions of the xylem mass are gradually abandoned by the ascending water (‘‘sap”), often change in color, and form the heart-wood. The younger portion, through which the sap is moving, is the sup-wood. It is evident, however, that the annual ad- ditions to the phloem are not in a position for permanency. The new phloem is deposited inside of the old, and this, to- gether with the new xylem, presses upon the old phloem, which becomes ruptured in various ways, and rapidly or very gradually peels off, being constantly renewed from within. Itis the protecting layers of cork (see this section under Cortez), the old phloem, and the new phloem down to the cambium, which constitute the so-called bark of trees, a structure exceedingly complex and extremely vari- able in different trees. The stele also frequently develops stereome tissue in the form of sclerenchyma. These thick-walled fibers are often closely associated with one or both of the vascular strands of the bundles (Fig. 270), and lead to the old name jidro- vascular bundles. To sum up, the stems of Dicotyledons and Conifers are characterized by the development of a vascular cylinder, in which the bundles are collateral and open, permitting increase in diameter, extension of the branch system, and a continuous increase in leaf display. 152. Monocotyl stems—In the stems of Monocotyledons there is the same apical development and differentiation (Fig. 266). The characteristic difference from the Dicotyl and Conifer type, just described, is in connection with the development of the vascular bundles in the stele. Instead of outlining a hollow cylinder, the bundles are scattered 290 PLANT STRUCTURES through the stele (Fig. 214). This lack of regularity would interfere with the organization of a cambium cylinder, and we find the bundles collateral but closed—that is, with no meristem left between the xylem and phloem (Fig. 271). Fig. 271. Cross-section of a closed collateral bundle from the stem of corn, showing the xylem with annular (7), spiral (s), and pitted (g) vessels: the phloem contain- ing sieve vessels (v), and separated from the xylem by no intervening cambium; both xylem and phloem surrounded by 2 mass of sclerenchyma (fibers); and in- vesting vessels and fibers the parenchyma (p) of the pith-like tissue through which the bundles are distributed.—After Sacus. This lack of cambium means that stems living for sev- eral years do not increase in diameter, but become columnar DIFFERENTIATION OF TISSUES 291 shafts, as in the palm, rather than much elongated cones. It also means lack of ability to develop an extending branch system or to display more numerous leaves each year. The palm may be taken as a typical result of such a structure, with its columnar and unbranched trunk, and its foliage crown containing about the same number of leaves each year. The lack of regular arrangement of the bundles also prevents the outlining of a pith region or the organization of definite pith rays. The failure to increase in diameter also precludes the necessity of bark, with its protective cork constantly renewed, and its sloughing-off phloem. To sum up, the stems of the Monocotyledons are characterized by the vascular bundles not developing a cylinder or any regular arrangement, and by collateral and closed bundles, which do not permit increase in diameter, or a branch system, or increase in leaf display. 153. Pteridophyte stems.—The stems of Pteridophytes are quite different from those of Spermatophytes. While the large Club- mosses (Lyco- podium) and Iscetes usually have an apical group of meris- tem cells, as among the Seed- plants, the smaller Club-mosses (Selaginella), Ferns, and Horse- tails usually have a single api- cal cell, whose divisions give rise to all the cells of the stem. Fig. 272. Diagram of tissues in cross- section of stem of a fern (Pferis), Generally also a dermatogen is showing two masses of scleren- ast aa * - chyma (sf), between and about not organized, and in such which are vascular bundles. — cases there isno true epidermis, — Cuamperrar. the cortex developing the ex- ternal protective tissue. In the cortex there is usually an extensive development of stereome. in the form of scleren- chyma (Fig. 272), the stele furnishing little or none, and the vascular bundles not adding much to the rigidity, as they do in the Seed-plants. 299 PLANT STRUCTURES In Equasetum and Isocetes the vascular bundles may be said to be collateral, as in the Seed-plants, but the charac- teristic Pteridophyte type is very different. In fact, the vascular masses can hardly be compared with the bundles of the Seed-plants, although they are called bundles for convenience. In the stele one or more of these bundles are organized (Fig. 272), the tracheary vessels (xylem) being in the center and completely invested by the sieve vessels Fic. 278. Cross-section of concentric vascular bundle of a fern (Pteris): the single row of shaded cells investing the others is the bundle sheath; the large and heavy- walled cells within constitute the xylem; and between the xylem and the bundle sheath is the phloem.—CHAMBERLAIN. (phloem). This is called the concentric bundle (Fig. 273), as distinguished from the collateral bundles of Seed-plants, and is characteristic of Pteridophyte stems. DIFFERENTIATION OF TISSUES 993 154. Roots—True roots appear only in connection with the vascular plants (Pteridophytes and Spermatophytes) ; and in all of them the structure is essentially the same, and quite different from stem structure. A single ap- ical cell (in most Pteridophytes) (Fig. 274) or an apical group (in Spermatophytes) usually gives rise to the three embryonic regions—dermatogen, periblem, and plerome (Fig. 275). A fourth region, how- ever, peculiar to root, is usually added. The apical Fie. 274. Section through root-tip of Fig. 275. A longitudinal section through Pteris,; the cell with a nucleus is the the root-tip of shepherd’s purse, single apical cell, which in front has showing the plerome (p/), surround- cut off cells which organize the root- ed by the periblem (p), outside of cap.—CHAMBERLAIN. periblem the epidermis (e) which disappears in the older parts of the cell or group cuts off a tis- root, and the prominent root-cap (¢). —From ‘Plant Relations.” sue in front of itself (Fig. 274), known as the calyptrogen, or “cap producer,” for it organizes the root-cap, which protects the delicate meri- stem of the growing point. Another striking feature is that in the stele there is organized a single solid vascular cylinder, forming a tough central axis (Fig. 277), from which the usually well-devel- oped cortex can be peeled off as a thick rind. In this vas- cular axis, which is called ‘‘a bundle ” for convenience but does not represent the bundle of Seed-plant stems, the ar- rangement of the xylem and phloem is entirely unlike that 37 294 PLANT STRUCTURES Fie. 276. Cross-section of the vascular axis of a root, showing radiate type of bundle the xylem (y) and phloem (pf) alternating. —After Sacus. found in stems. The xylem is in the center and sends out a few radiating arms, between which are strands of phloem, Fie, 277. Endogenous origin of root branch- es, showing them (2) arising from the cen- tral axis (7) and breaking through the cortex (7).—After VINEs. forming the so-called radiate bundle (Fig. 276). This arrangement brings the tracheary vessels (xylem) to the surface of the bundle region, which is not true of either the concentric or collateral bundle. This seems to be associated with the fact that the xylem is to receive and conduct the water absorbed from the soil. It should be said that this characteristic DIFFERENTIATION OF TISSUES 295 bundle structure of the root appears only in young and active roots. In older ones certain secondary changes take place which obscure the structure and result in a resem- blance to the stem. The origin of branches in roots is also peculiar. In stems branches originate at the surface, involving epi- dermis, cortex, and vascular bundles, such an origin being called exogenous (** produced outside“); but in roots branches originate on the vascular cylinder, burrow through the cortex, and emerge at the surface (Fig. 277). If the cortex be stripped off from a root with branches, the branches are left attached to the woody axis, and the cor- tex is found pierced with holes made by the burrowing branches. Such an origin is called exdogenoux, meaning ** produced within.” To sum up the peculiarities of the root, it may be said to develop a root-cap. to have a solid vascular cylinder in which the xylem and phloem are arranged to form a bundle of the radiate type, and to branch endogenously. Z fe sh ST Fie. 278. A section through the leaf of lily, showing upper epidermis (we), lower epi- dermis (/e) with its stomata (sf), mesophyll (dotted cells) composed of the palisade region (p) and the spongy region (sp) with air spaces among the cells. and two veins (v) cut across.—From * Plant Relations.” 296 PLANT STRUCTURES 155. Leaves—Leaves usually develop from an apical region in the same general way as do stems and roots, modified by their common dorsiventral character. Com- paring the leaf of an ordinary seed-plant with its stem, it will. be noted that the three regions are represented (Fig. 278): (1) the epidermis ; (2) the cortex, represented by the mesophyll ; (3) the stele, represented by the veins. In the case of collateral bundles, where in the stem the xylem is always toward the center and the phloem is toward the circumference, in the leaves the xylem is toward the upper and the phloem toward the lower surface. CHAPTER XVI PLANT PHYSIOLOGY 156. Introductory.—Plants may be studied from several points of view, each of which has resulted in a distinct division of Botany. The study of the forms of plants and their structure is MoRPHOLOGY, and it is this phase of Bot- any which has been chiefly considered in the previous chap- ters. The study of plants at work is PaysioLoGy, and as structure is simply preparation for work, the preceding chapters have contained some Physiology, chiefly in refer- ence to nutrition and reproduction. The study of the clas- sification of plants is Taxonomy, and in the preceding pages the larger groups have been outlined. The study of plants as to their external relations is EcoLoey, a subject which will be presented in the following chapter, and which is the chief subject of Plant Relations. The study of the diseases of plants and their remedies is ParnoLoey ; their study in relation to the interests of man is Economic Borany. Besides these general subjects, which apply to all plants, the different groups form the subjects of special study. The study of the Morphology, Physiology, or Taxonomy of the Bacteria is Bacteriology ; of the Alge, Algology; of the Fungi, Mycology; of the Bryophytes, Bryology ; of the fossil plants, Paleobotany or Paleophytology, etc. In the present chapter it is the purpose to give a very brief outline of the great subject of Plant Physiology, not with the expectation of presenting its facts adequately, but with the hope that the important field thus presented may 297 298 PLANT STRUCTURES attract to further study. It is merely the opening of a door to catch a fleeting glimpse. A common division of the subject presents it under five heads: (1) Stability of form, (2) Nutrition, (3) Respira- tion, (4) Movement, (5) Reproduction. STABILITY OF FORM 157. Turgidity.—It is a remarkable fact that plants and parts of plants composed entirely of cells with very thin and delicate walls are rigid enough to maintain their form. It has already been noted (see § 20) that such active cells exert an internal pressure upon their walls. This seems to be due to the active absorption of liquid, which causes the very elastic walls to stretch, as in the ‘‘ blowing up ” of a bladder. In this way each gorged and distended cell be- comes comparatively rigid, and the mass of cells retains its form. It seems evident that the active protoplasm greedily pulls liquid through the wall and does not let it escape so easily. If for any reason the protoplasm of a gorged cell loses its hold upon the contained liquid the cell collapses. 158. Tension of tissues—The rigidity which comes to active parenchyma cells through their turgidity is increased by the tensions developed by adjacent tissues. For exam- ple, the internal and external tissues of a stem are apt to increase in volume at different rates; the faster will pull upon the slower, and the slower will resist, and thus be- tween the two a tension is developed which helps to keep them rigid. This is strikingly shown by splitting a dande- lion stem, when the inner tissue, relieved somewhat from the resistance of the outer, elongates and causes the strip to become strongly curved outward or cven coiled. Experi- ments with strips from active twigs, including the pith, will usually demonstrate the same curve outward. Tension of tissues is chiefly developed, of course, where elongation is taking place. PLANT PHYSIOLOGY 299 159. Stereome—When growth is completed, cell walls lose their elasticity. turgidity becomes less, and therefore tensions diminish, and rigidity is supplied by special ster- eome tissues, chief among which is sclerenchyma. An- other stereome tissue is collenchyma, which on account of its elastic walls can be used to supplement turgidity and tension where elongation is still going on. For a fuller account of stereome tissues see § 150. NUTRITION 160. Food—Plant food must contain carbon (C), hydro- gen (H), oxygen (Q), and nitrogen (N). and also more or less of other elements, notably sulphur, phosphorus, potassium, calcium, magnesium, and iron. In the case of green plants these elements are obtained from inor- ganic compounds and food is manufactured ; while plants without chlorophyll obtain their food already organized. The sources of these elements for green plants are as follows: Carbon from carbon dioxide (CQ,) of the air; hydrogen and oxygen from water (H,0):; and nitrogen and the other elements from their various salts which occur in the soil and are dissolved in the water which enters the plant. All of these substances must present themselves to plants in the form of a gas or a liquid, as they must pass through cell walls: and the processes of absorption have to do with the taking in of the gas carbon dioxide and of water in which the necessary salts are dissolved. 161. Absorption.—Green plants alone will be considered, as the unusual methods of securing food have been men- tioned in Chapter VII. For convenience also, only terres- trial green plants will be referred to, as it is simple to modify the processes to the aquatic habit, where the sur- rounding water supplies what is obtained by land plants from both air and soil. 300 PLANT STRUCTURES In such plants the carbon dioxide is absorbed directly from the air by the foliage leaves, whose expanse of surface is as important for this purpose as for exposing chlorophyll to light. When the work of foliage leaves is mentioned it must always be understood that it applies as well to any green tissue displayed by the plant. The water, with its dissolved salts, is absorbed from the soil by the roots. Only the youngest parts of the root- system can absorb, and the absorbing capacity of these parts is usually vastly increased by the development of numerous root hairs just behind the growing tip (Fig. 194). These root hairs are ephemeral, new ones being continu- ally put out as the tip advances, and the older ones disap- pearing. They come in very close contact with the soil particles, and ‘suck in” the water which invests each particle as a film. 162. Transfer of water.—The water and its dissolved salts absorbed by the root-system must be transferred to the foli- age leaves, where they are to be used, along with the carbon dioxide, in the manufacture of food. Having entered the epidermis of the absorbing rootlets the water passes on to the cortex, and traversing it enters the xylem system of the central axis. In some way this transfer is accompanied by pressure, known as root pres- sure, which becomes very evident when an active stem is cut off near the ground. The stump is said to “bleed,” and sends out water (‘‘sap”) as if there were a force pump in the root-system. This root pressure doubtless helps to lift the water through the xylem of the root into the stem, and in low plants may possibly be able to send it to the leaves, but for most plants this is not possible. When the water enters the xylem of the root it is ina continuous system of vessels which extends through the stem and out into the leaves. The movement of the ab- sorbed water through the xylem is called the transpiration current, or very commonly the ‘‘ascent of sap.” An ex- PLANT PHYSIOLOGY 301 periment demonstrating this ascent of sap and its route through the xylem will be found described in Plant [ela- tions, p. 151. How it is that the transpiration current moves through the xylem is not certainly known. 163. Transpiration— When the water carrying dissolved salts reaches the mesophyll cells, some of the water and all of the salts are retained for food manufacture. However, much more water enters the leaves than is needed for food, this excess having been used for carrying soil salts. When the soil salts have reached their destination the excess of water is evaporated from the leaf surface, the process being called transpiration. For an experiment demonstrating transpiration see Plant Relations, § 26. This transpiration is regulated according to the needs of the plant. If the water is abundant, transpiration is encouraged ; if the water supply is low, transpiration is checked. One of the chief ways of regulating is by means of the very small but exceedingly numerous stomata (see § 79 [4]), whose guard cells become turgid or collapse and so determine the size of the opening between them. It has been estimated that a leaf of an ordinary sunflower contains about thirteen million stomata, but the number varies widely in different plants. In ordinary dorsiventral leaves the sto- mata are much more abundant upon the lower surface than upon the upper, from which they may be lacking entirely. In erect leaves they are distributed equally upon both sur- faces ; in floating leaves they occur only upon the upper surface ; in submerged leaves they are lacking entirely. The amount of water thus evaporated from active leaves is very great. It is estimated that the leaves of a sunflower as high as a man evaporate about one quart of water in a warm day; and that an average oak tree in its five active months evaporates about twenty-eight thousand gallons. If these figures be applied to a meadow or a forest the result may indicate the large importance of this process. 802 PLANT STRUCTURES 164. Photosynthesis—This is the process by which car- bon dioxide and water are “broken up,” their elements recombined to form a carbohydrate, and some oxygen given off as a waste product, the mechanism being the chloroplasts and light. It has been sufficiently described in § 55, and also in Plant Relations, pp. 28 and 150. 165. Formation of proteids—The carbohydrates formed by photosynthesis, such as starch, sugar, etc., contain car- bon, hydrogen, and oxygen. Ont of them the living cells must organize proteids, and in the reconstruction nitrogen and sulphur, and sometimes phosphorus, are added. This work goes on both in green cells and other living cells, as it does not seem to be entirely dependent upon chloroplasts and light. 166. Transfer of carbohydrates and proteids——These two forms of food having been manufactured, they must be carried to the regions of growth or storage. In order to be transported they must be in soluble form, and if not already soluble they must be digested, insoluble starch being con- verted into soluble sugar, etc. In these digested forms they are transported to regions where work is going on, and there they are assimilated—that ‘is, transformed into the enormously complex working substance protoplasm ; or they are transported to regions of storage and there they are reconverted into insoluble storage forms, as starch, etc. These foods pass through both the cortex and phloem in every direction, but the long-distance transfer of pro- teids, as from leaves to roots, seems to be mainly through the sieve vessels. RESPIRATION 167. Respiration.—This is an essential process in plants as well as in animals, and is really the phenomenon of “breathing.” The external indication of the process is the absorption of oxygen and the giving out of carbon di- oxide ; and it goes on in all organs, day and night. When PLANT PHYSIOLOGY 303 it ceases death ensues sooner or later. By this process energy, stored up by the processes of nutrition, is liberated, and with this liberated energy the plant works. It may be said that oxygen seems to have the power of arousing pro- toplasm to activity. It is not sufficient for the air containing oxygen to come in contact merely with the outer surface of a complex plant, as its absorption and transfer would be too slow. There must be an ‘internal atmosphere” in contact with the living cells. This is provided for by the intercellular spaces, which form a labyrinthine system of passageways, opening at the surface through stomata and lenticels (pores through bark). In this internal atmosphere the exchange of oxygen and carbon dioxide is effected, the oxygen being renewed by diffusion from the outside, and the carbon dioxide finally escaping by diffusion to the outside. MOVEMENT 168. Introductory.—In addition to movements of mate- rial, as described above, plants execute movements depend- ent upon the activity of protoplasm, which result in change of position. Naked masses of protoplasm, as the plas- modium of slime-moulds (see § 51), advance with a sliding, snail-like movement upon surfaces ; zoospores and ciliated sperms swim freely about by means of motile cilia; while many low plants, as Bacteria (§ 52), Diatoms (§ 34), Osetl- laria (§ 20), ete., have the power of locomotion. When the protoplasm is confined within rigid walls and tissues, as in most plants, the power of locomotion usually disappears, and the plants are fixed ; but within active cells the protoplasm continues to move, streaming back and forth and about within the confines of the cell. In the case of complex plants, however, another kind of movement is apparent, by which parts are moved and variously directed, sometimes slowly, sometimes with great 304 PLANT STRUCTURES rapidity. In these cases the part concerned develops a curvature, and by various curvatures it attains its ultimate position. These curvatures are not necessarily permanent, for a perfectly straight stem results from a series of cur- vatures near its apex. Curvatures may be developed by unequal growth on the two sides of an organ, or by unequal turgidity of the cells of the two sides, or by the unequal power of the cell walls to absorb water. 169. Hygroscopic movements.—These movements are only exhibited by dry tissues, and hence are not the direct result of the activity of protoplasm. The dry walls absorb mois- ture and swell up, and if this absorption of moisture and its evaporation is unequal on two sides of an organ a curva- ture will result. In this way many seed vessels are rup- tured, the sporangia of ferns are opened, the operculum of mosses is lifted off by the peristome, the hair-like pappus of certain Composites is spread or collapsed, certain seeds are dispersed and buried, etc. One of the peculiarities of this hygroscopic power of certain cells is that the result may be obtained through the absorption of the moisture of the air, and the hygroscopic awns of certain fruits have been used in the manufacture of rough hygrometers (‘* measures of moisture ”). 170. Growth movements.—Growth itself is a great physi- ological subject, but certain movements which accompany it are referred to here. Two kinds of growth movements are apparent. One may be called nutation, by which is meant that the growing tip of an organ does not advance in a straight line, but bends now toward one side, now toward the other. In this way the tip describes a curve, which may be a circle, or an ellipse of varying breadth; but as the tip is advancing all the time, the real curve described is a spiral with circular or elliptical cross-section. The sweep of a young hop-vine in search of support, or of various tendrils, may be taken as extreme illustrations, but in most cases PLANT PHYSIOLOGY 305 the nutation of growing tips only becomes apparent through prolonged experiment. The other prominent growth movement is that which places organs in proper relations for their work, sending roots into the soil and stems into the air, and directing leaf planes in various ways. For example, in the germina- tion of an ordinary seed, in whatever direction the parts emerge the root curves toward the soil, the stem turns upward, and the cotyledons spread out horizontally. The movement of nutation seems to be due largely to internal causes, while the movements which direct organs are due largely to external causes known as stimuli, Some of the prominent stimuli concerned in directing organs are as follows: Heliotropism.—tIn this case the stimulus is light, and under its influence acrial parts are largely directed. Plants growing in a window furnish plain illustration of helio- tropism. In general the stems and petioles curve toward the light, showing positive heliutropism (Fig. 279); the leaf blades are directed at right angles to the rays of light, showing transverse heliotropism ; while if there are hold- fasts or aérial roots they are directed away from the light, showing negative heliotropism. The thallus bodies of ferns, liverworts, etc., are transversely heliotropic, as ordinary leaves. a position best related to chlorophyll work. If the light is too intense, leaves may assume an edgewise or pro- file position, a condition well illustrated by the so-called “compass plants.” (See Plant Relations, p. 10.) Geotropism.—In this case the stimulus is gravity, and its influence in directing the parts of plants is very great. All upward growing plants, as ordinary stems. some leaves, etc.. are negatively geotropic, growing away from the center of gravity. Tap-roots are notable illustrations of positive geotropism, growing toward the source of gravity with con- siderable force. Lateral branches from a main or tap-root, however. are usually transversely geotropic. Fic, 279. Sunflower stems with the upper part of the stem sharply bent toward the light, giving the leaves better exposure, the stem showing positive heliotropism,— After SCHAFPNER. PLANT PITYSIOLOGY 307 That these influences in directing are very real is testi- fied to by the fact that when the organs are turned aside from their proper direction they will curve toward it and overcome a good deal of resistance to regain it. Although these curvatures are mainly developed in growing parts, even mature parts which have been displaced may be brought back into position. For example, when the stems of certain plants, notably the grasses, have been prostrated by wind, etc., they often can resume the erect position under the influence of negative geotropism, a very strong and even angular curvature being developed at certain joints. Hydrotropism.—The influence of moisture is very strong in directing certain organs, notably absorbing systems. Roots often wander widely and in every direction under the guidance of hydrotropism, even against the geotropic influence. Ordinarily geotropism and hydrotropism act in the same direction, but it is interesting to dissociate them so that they may “‘ pull” against one another. For such an experiment see Plant Relutionsx, p. 91. Other stimuli.—Other outside stimuli which have a directive influence upon organs are chemical substances (chemotropism), such as direct sperms to the proper female organ ; heat (¢hermofrapism) ; water currents (rheotrapism) ; mechanical contact, etc. The most noteworthy illus- trations of the effect of contact are furnished by tendril- climbers. When a nutating tendril comes in contact with a support a sharp curvature is developed which grasps it. In many cases the irritable response goes further. the ten- dril between the plant axis and the support developing a spiral coil. 171. Irritable movements—The great majority of plants can execute movements only in connection with growth, as described in the preceding section, and when mature their parts are fixed and incapable of further adjustment. Cer- tain plants, however, have developed the power of moving mature parts, the motile part always being a leaf, such as 308 PLANT STRUCTURES foliage leaf, stamen, etc. It is interesting to note that these movements have been cultivated by but few families, nota- ble among them being the Legumes (§ 141). These movements of mature organs, some of which are very rapid, are due to changes in the turgidity of cells. As already mentioned (§ 157), turgid cells are inflated and rigid, and when turgidity ceases the cells collapse and the tissue becomes flaccid. A special organ for varying tur- gidity, known as the pulvinus, is usually associated with the motile leaves and leaflets. The pulvinus is practically a mass of parenchyma cells, whose turgidity is made to vary by various causes, and leaf-movement is the result. The causes which induce some movements are unknown, as in the case of Desmodium gyrans (see Plant Relations, p. 49), whose small lateral leaflets uninterruptedly de- scribe circles, completing a cycle in one to three minutes. In other cases the inciting cause is the change from light to dark, the leaves assuming at night a very dif- ferent position from that during the day. Dur- ing the day the leaflets are spread out freely, Fig. 280. A leaf of a sensitive plant in two conditions: in the figure to the left the leaf is fully expanded, with its four main divisions and numcrous leaflets well spread; in the figure to the right is shown the same leaf after it has been ‘‘shocked”’ by a sudden touch, or by sudden heat, or in some other way; the leaflets have been thrown together forward and upward, the four main divisions have been moved together, and the main leaf-stalk has been directed sharply downward,—After DucuaRTRE. PLANT PHYSIOLOGY 309 while at night they droop and usually fold together (see Plant Relutions, pp. 9, 10). These are the so-called nycti- tropic movements or *‘ night movements,” which may be ob- served in many of the Legumes, as clover, locust, bean, etc. In still other cases, mechanical irritation induces move- ment, as sudden contact, heat, injury, etc. Some of the “carnivorous plants” are notable illustrations of this, es- pecially Dionea, which snaps its leaves shut like a steel trap when touched (see Plunt Relutivns, p. 161). Among the most irritable of plants are the so-called *‘ sensitive plants,” species of Mimosa, Acacia, ete., all of them Le- gumes. The most commonly cultivated sensitive plant is Uimnosa pudica (Fig. 280), whose sensitiveness to contact and rapidity of response are remarkable (see Plant Rela- tions, p. 48). REPRODUCTION 172. Reproduction.—The important function of repro- duction has been considered in connection with the various plant groups. Among the lowest plants the only method of reproduction is cell division, which in the complex forms results in growth. In the more complex plants va- rious outgrowths or portions of the body, as gemme, buds, bulbs, tubers, various branch modifications, etc., furnish means of propagation. All of these methods are included under the head of vegetative multiplication. as the plants are propagated by ordinary vegetative tissues. When a special cell is organized for reproduction, dis- tinct from the vegetative cells. it is called a spore, and re- production by spores is introduced. The first spores devel- oped seem to have been those produced by the division of the contents of a mother cell. and are called axerval spores. These spores are scattered in various ways—by swimming (zoospores), by floating, by the wind, by insects. Another type of spore is the serval spore. formed by the union of two sexual cells called gametes. The gametes 38 310 PLANT STRUCTURES seem to have been derived from asexual spores. At first the pairing gametes are alike, but later they become differ- entiated into syerms or male cells, and eggs or female cells. With the establishment of alternation of generations, the asexual spores are restricted to the sporophyte, and the gametes to the gumetophyte. With the further introduction of heterospory, the male and the female gametes are sepa- rated upon different gametophytes, which become much reduced. With the reduction of the megaspores to one in a spo- rangium (ovule), and its retention, the seed is organized, and the elaborate scheme of insect-pollination is developed. CHAPTER XVII PLANT ECOLOGY 173. Introductory.— Ecology has to do with the external relations of plants, and forms the principal subject of the volume entitled Plant Relations, which should be consulted for fuller descriptions and illustrations. It treats of the adjustment of plants and their organs to their physical surroundings, and also their relations with one another and with animals, and has sometimes been called ‘plant sociology.” LIFE RELATIONS 174. Foliage leaves.—The life relation essential to foliage leaves is the relation to light. This is shown by their positions and forms, as well as by their behavior when deprived of light. This light relation suggests the answer to very many questions concerning leaves. It is not very important to know the names of different forms and differ- ent arrangements of leaves, but it is important to observe that these forms and arrangements are in response to the light relation. In general a leaf adjusts its own position and its relation to its fellows so as to receive the greatest amount of light. Upon erect stems the leaves occur in vertical rows which are uniformly spaced about the circumference. If these rows are numerous the leaves are narrow; if they are few the leaves are usually broad. If broad leaves were associ- ated with numerous rows there would be excessive shading ; 311 312 PLANT STRUCTURES if narrow leaves were associated with few rows there would be waste of space. It is very common to observe the lower leaves of a stem long-petioled, those above short-petioled, and so on until the uppermost have sessile blades, thus thrusting the blades of lower leaves beyond the shadow of the upper leaves. There may also be a gradual change in the size and direc- tion of the leaves, the lower ones being relatively large and horizontal, and the upper ones gradually smaller and more directed upward. In the case of branched (compound) leaves the reduction in the size of the upper leaves is not so necessary, as the light strikes between the upper leaflets and reaches those below. On stems exposed to light only or chiefly on one side, the leaf blades are thrown to the lighted side in a variety of ways. Inivies, many prostrate stems, horizontal branches of trees, etc., the leaves brought to the lighted side are observed to form regular mosaics, each leaf interfering with its neighbor as little as possible. There is often need of protection against too intense light, against chill, against rain, etc., which is provided for in a great variety of ways. Coverings of hairs or scales, the profile position, the temporary shifting of position, rolling up or folding, reduction in size, etc., are some of the common methods of protection. 175. Shoots—The stem is an organ which is mostly related to the leaves it bears, the stem with its leaves being the shoot. In the foliage-bearing stems the leaves must be displayed to the light and air. Such stems may be sub- terranean, prostrate, floating, climbing, or erect, and all of these positions have their advantages and disadvantages, the erect type being the most favorable for foliage display. In stems which bear scale leaves no light relation is necessary, so that such shoots may be and often are sub- terranean, and the leaves may overlap, as in scaly buds and bulbs. The subterranean position is very favorable PLANT ECOLOGY 313 for food storage, and such shoots often become modified as food depositories, as in bulbs, tubers, rootstocks, ete. In the scaly buds the structure is used for protection rather than storage. The stem bearing floral leaves is the shoot ordinarily called “the flower,” whose structure and work have been sufficiently described. Its adjustments have in view polli- nation and seed dispersal, two very great ecological sub- jects full of interesting details. 176. Roots.—Roots are absorbent organs or holdfasts or both, and ‘they enter into a variety of relations. Most common is the soil relation, and the energetic way in which such roots penetrate the soil, and search in every direction for water and absorb it, proves them to be highly organized members. Then there are roots related to free water, and others to air, each with its appropriate struc- ture. More mechanical are the clinging roots (ivies, etc.), and prop roots (screw pines, banyans, etc.), but their adap- tation to the peculiar service they render is none the less interesting. The above statements concerning leaves, shoots, and roots should be applied with necessary modifications to the lower plants which do not produce such organs. The light relation and its demands are no less real among the Alge than among Spermatophytes, as well as relations to air, soil, water, mechanical support, etc. PLANT SOCIETIES 177. Introductory—Plants are not scattered at hap- hazard over the surface of the earth, but are organized into definite communities. These communities are deter- mined by the conditions of living—conditions which admit some plants and forbid others. Such an association of plants living together in similar conditions is a plant so- ciety. Closely related plants do not usually live together 314 PLANT STRUCTURES in the same society, as their rivalry is too intense; but each society is usually made up of unrelated plants which can make use of the same conditions. There are numerous factors which combine to deter- mine societies, and it is known as yet only in a vague way how they operate. 178. Ecological factors— Water.—This is a very impor- tant factor in the organization of secieties, which are usu- ally local associations. Taking plants altogether, the amount of water to which they are exposed varies from complete submergence to perpetual drought, but within this range plants vary widely as to the amount of water necessary for living. Heat.—In considering the general distribution of plants over the surface of the earth, great zones of plants are out- lined by zones of temperature ; but in the organization of local societies in any given area the temperature condi- tions are nearly uniform. Usually plants work only at temperatures between 32° and 122° Fahr., but for each plant there is its own range of temperature, sometimes extensive, sometimes restricted. Even in plant societies, however, the effect of the heat factor may be noted in the succession of plants through the working season, spring plants being very different from summer and autumn plants. Soil.—The great importance of this factor is evident, even in water plants, for the soil of the drainage area deter- mines the materials carried by the water. Soil is to be considered both as to its chemical composition and its physical properties, the latter chiefly in reference to its disposition toward water. Soils vary greatly in the power of receiving and retaining water, sand having a high recep- tive and low retentive power, and clay just the reverse, and these factors have large effect upon vegetation. Light.—All green plants can not receive the same amount of light. Hence some of them have learned to live with a PLANT ECOLOGY 315 less amount than others, and are ‘‘shade plants” as dis- tinct from “light plants.” In forests and thickets many of these shade plants are to be seen, which would find an exposed situation hard to endure. In almost every society, therefore, plants are arranged in strata, dependent upon the amount of light they receive, and the number of these strata and the plants characterizing each stratum are im- portant factors to note. Wind.—This is an important factor in regions where there are strong prevailing winds. Wind has a drying effect and increases the transpiration of plants, tending to impoverish them in water. In such conditions only those plants can live which are well adapted to regulate tran- spiration. The above five factors are among the most important, but no single factor determines a society. As each factor has a large possible range, the combinations of factors may be very numerous, and it is these combinations which de- termine societies. For convenience, however, societies are usually grouped on the basis of the water factor, at least three great groups being recognized. 179. Hydrophyte societies—These are societies of water plants, the water factor being so conspicuous that the plants are either submerged or standing in water. A plant completely exposed to water, submerged, or floating, may be taken to illustrate the usual adaptations. The epi- dermal walls are thin, so that water may be absorbed through the whole surface; hence the root system is very commonly reduced or even wanting ; and hence the water- conducting tissues (xylem) are feebly developed. The tis- sues for mechanical support (stereome) are feebly devel- oped, the plant being sustained by the buoyant power of water. Such a plant, although maintaining its form in water, collapses upon removal. Very common also is the development of conspicuous air passages for internal aéra- tion and for increasing buoyancy ; and sometimes a special 316 PLANT STRUCTURES buoyancy is provided for by the development of bladder- like floats. Conspicuous among hydrophyte societies may be men- tioned the following: (1) Free-swimming societies, in which the plants are entirely sustained by water, and are free to move either by locomotion or by water currents. Here belong the ‘plankton societies,” consisting of minute plants and animals invisible to the naked eye, conspicuous among the plants being the diatoms ; also the ‘‘ pond so- cieties,” composed of alge, duckweeds, etc., which float in stagnant or slow-moving waters. (2) Pondweed societies, in which the plants are an- chored, but their bodies are submerged or floating. Here belong the ‘‘rock societies,” consisting of plants anchored to some firm support under water, the most conspicuous forms being the numerous fresh-water and marine alge, among which there are often elaborate systems of holdfasts and floats. The ‘loose-soil societies” are distinguished by imbedding their roots or root-like processes in the mucky soil of the bottom (Figs. 281, 282). The water lilies with their broad floating leaves, the pondweeds or pickerel weeds with their narrow submerged leaves, are conspicuous illus- trations, associated with which are alge, mosses, water ferns, etc. (3) Swamp societies, in which the plants are rooted in water, or in soil rich in water, but the leaf-bearing stems rise above the surface. The conspicuous swamp societies are ‘reed swamps,” characterized by bulrushes, cat-tails and reed-grasses (Figs. 283, 28+), tall wand-like Monocoty- ledons, usually forming a fringe about the shallow margins of small lakes and ponds; ‘‘swamp-moors,” the ordinary swamps, marshes, bogs, etc., and dominated by coarse sedges and grasses (Fig. 282); ‘‘swamp-thickets,” consist- ing of willows, alders, birches, etc. ; ‘* sphagnum-moors,” in which sphagnummoss predominates, and is accompanied by numerous peculiar orchids, heaths, carnivorous plants, etc. ; “TTA MALY J—'SOTIP DOPBM TOJWOD OY UL PYVUPUAT, LIV OPT Jpop ety oO} :Addod aoqua Mod OY] WT oy] OF piu p Folop ott, ut s(sopkydoapay) spun oywa jo duos y—'[Ry “Py “SIMAT TAL Aq ydrasojoyd wlory— Ajyawos daaj vB punossyorq oy] Ur pue ‘Kjoroos quays vB UaTy ‘YoRq sans sassvrs duvas oqul Surpuas ojem Jo upaceur ye sospas ‘puod ATIL PSMOT[OJ SB SaIJoIN0s oTAYdosew 09 oy {YdoupAY Worf u J] SULMOYsS ‘satjalv0s JuLld Jo soles Yo ‘eRe “OTL iy PLANT ECOLOGY 319 ““swamp-forests,” which are largely coniferous, tamarack (larch), pine, hemlock, etc., prevailing. showing the reed swamp growth of rushes and sedyes,—Cow Les. Shore of Calionet Lake, OL, 283. Kia. 180. Kerophyte societies—These societies are exposed to the other extreme of the water factor, and are composed of plants adapted to dry air and soil. To meet these B20 PLANT STRUCTURES drought conditions numerous adaptations have been de- veloped and are very characteristic of xerophytic plants. Some of the conspicuous adaptations are as follows: peri- water, eventually leading to fillmg up.—Cow es. Fig. 284, The border of Lake Calumet, Ill., showing the advance of sedges and rushes into the deeper odic reduction of surface, annuals bridging over a period of drought in the form of seeds, geophilous plants also dis- appearing from the surface and persisting in subterranean “TIANA TVO—'S]UL[d-poos puv ‘sutoy ‘sassolT ‘S]IOMIOAT, ‘SUOTT, ‘uN SUB[W JO SPUN SNOLIBA LB sOTpoOL BUBUUUOAG oY} Apu) “UT Bony) vou AJoLIOs Yoot popuys Wo "GRE “HLT “TIAMGIVO— AJaIN0s Yoor ayfLydosax v Ssurwm1z0f szuvtd aotaeid Joyo YA Zuope ‘saad YOOL ay} Ul Surmoas (sourd ApPysout) soot] FUMOYS “voy /) LVAU AVATY SIOUT[[] UO ,.“YIOY poarwyg., "98s “NLT RRO G “ITAMATY,) PUR SETMODQ—‘SOOLANID YOO OY UT aTvaoTouV aavy YOuypM Ypo oy Jo o8po oy) 1910 sjoor yuos svy ouId oyWM Yo ‘saed) pur squats Jo Apatyo pasyoduos M1908 TID Vo LBS PL 824 PLANT STRUCTURES parts, deciduous trees and shrubs dropping their leaves, etc. ; temporary reduction of surface, the leaves rolling up or folding together in various ways; profile position, the leaves standing edgewise and not exposing their flat sur- faces to the most intense light; motile leaves which can shift their position to suit their needs ; small leaves, a very characteristic feature of xerophytic plants; coverings of hair; dwarf growth; anatomical adaptations, such as cuticle, palisade tissue, etc. Probably the most conspicu- ous adaptation, however, is the organization of ‘‘ water- reservoirs,” which collect and retain the scanty water sup- ply, doling it out as the plant needs it. Some of the prominent societies are as follows: ‘‘rock- societies ” composed of plants living upon exposed rock sur- faces, walls, fences, etc., notably lichens and mosses ; “sand societies,” including beaches, dunes, and sandy fields ; ‘‘shrubby heaths,” characterized by heath plants ; “plains,” the great areas of dry air and wind developed in the interiors of continents; “‘ cactus deserts,” still more arid areas of the Mexican region, where the cactus, agave, yucca, etc., have learned to live by means of the most ex- treme xerophytic modifications ; ‘‘ tropical deserts,” where xerophytic conditions reach their extreme in the combina- tion of maximum heat and minimum water; ‘‘ xerophyte thickets,” the most impenetrable of all thicket-growths, represented by the “chaparral” of the Southwest, and the “bush” and “scrub” of Africa and Australia; ‘‘ xero- phyte forests,” also notably coniferous. (See Figs. 285, 286, 287.) 181. Mesophyte societies—Mesophytes make up the com- mon vegetation, the conditions of moisture being medium, and the soil fertile. This is the normal plant condition, and is the arable condition—that is, best adapted for the plants which man seeks to cultivate. If a hydrophytic area is to be cultivated, it is drained and made mesophytic ; if a xerophytic area is to be cultivated, it is irrigated and ‘sMOqOIT JO Boum snow “TTS. OUD OLR TOLL MM TY, , y—'syuntd AL UE UT pa us Os pur wy avou STI} AY ‘9 SSOUL ‘3)I0 AAL YloOs | YVOL TUL OAT] lap oy YPQRIOUW VoCRRG. OT 39 ‘TIAMGTYO PUL SATAOO—, YOY PaamvjG,, IwoM ‘OAR STOUT[TT 94} UT “PuBys, Ue MBUIeU OF PUB ‘guoamo ayy fq [Jos oy} Jo Ave Surysvar oy} quoaoid s}001 SSO Ar Sood} puB squays Jo AJaTOOS YW "686 “PLL PLANT ECOLOGY 327 made mesophytic. As contrasted with hydrophyte and xero- phyte societies. the mesophyte societies are far richer in leaf forms and in general luxuriance. The artificial soci- eties which have been formed under the influence of man, through the introduction of weeds and culture plants. are all mesophytic. Among the mesophyte grass and herb societies are the ‘‘arctic and alpine carpets.” so characteristic of high lati- tudes and altitudes where the conditions forbid trees. shrubs, or even tall herbs : ‘‘ meadows,” areas dominated by grasses, the prairies being the greatest meadows, where crasses and flowering herbs are richly displaved ; ‘* pastures.” drier and more open than meadows. Among the woody mesophyte societies are the ‘ thick- ets.” composed of willow. alder, birch, hazel, etc., either pure or forming a jungle of mixed shrubs. brambles, and tall herbs: ‘‘ deciduous forests.” the glory of the temperate regions, rich in forms and foliage display. with annual fall of leaves. and exhibiting the remarkable and conspicuous phenomenon of autumnal coloration : ‘rainy tropical for- ests.” in the region of trade winds. heavy rainfalls, and great heat, where the world’s vegetation reaches its climax, and where in a saturated atmosphere gigantic jungles are developed, composed of trees of various heights, shrubs of all sizes. tall and low herbs, all bound together in an inex- tricable tangle by great vines or lianas, and covered by a luxuriant growth of numerous epiphytes. (See Figs. 233, 289.) GLOSSARY [The definitions of a glossary are often unsatisfactory. It is much better to con- sult the fuller explanations of the text by means of the index. The following glos- sary includes only frequently recurring technical terms. Those which are found only in reasonably close association with their explanation are omitted. The number fol- lowing each definition refers to the page where the term will be found most fully defined. } ACTINOMORPHIC: applied to a flower in which the parts in each set are similar; regular. 228. AKENE: a one-seeded fruit which ripens dry and seed-like. 212. ALTERNATION OF GENERATIONS: the alternation of gametophyte and sporophyte in a life history. 94, ANEMOPHILOUS: applied to flowers or plants which use the wind as agent of pollination, 181. ANISOCARPIC: applied to a flower whose carpels are fewer than the other floral organs. 268. ANTHER: the sporangium-bearing part of astamen. 197. ANTHERIDIUM: the male organ, producing sperms. 16. ANTIPODAL CELLS: in Angiosperms the cells of the female gametophyte at the opposite end of the embryo-sac from the egg-apparatus. 205. APETALOUS : applied to a flower with no petals. 221. APocaRPoUs: applied to a flower whose carpels are free from one an- other. 226. ARCHEGONIUM: the female, egg-producing organ of Bryrophytes, Pteri- dophrtes, and Gymnosperms. 100. ARCHESPORIUM : the first cell or group of cells in the spore-producing series. 102. AscocaRP: a special case containing asci. 58. AASCOSPORE : a spore formed within an ascus. 59. Ascus: a delicate sac (mother-cell) within which ascospores develop. 59. ASEXUAL SPORE: one produced usually by cell-division, at least not by cell-union. 9. 829 330 GLOSSARY CaLyx : the outer set of floral leaves. 221. CapsuLE: in Bryophytes the spore-vessel ; in Angiosperms a dry fruit which opens to discharge its seeds. 98, 211. Carpe: the megasporophyll of Spermatophytes. 178. CHLOROPHYLL: the green coloring matter of plants. 5. CuLoropLast: the protoplasmic body within the cell which is stained green by chlorophyll. 7. CoLUMELLA: in Bryophytes the sterile tissue of the sporogonium which is surrounded by the sporogenous tissue. 106. Conrpium : an asexual spore formed by cutting off the tip of the sporo- phore, or by the division of hyphe. 58. Consucation : the union of similar gametes. 15. Corouia: the inner set of floral leaves. 221. CoryLEpon : the first leaf developed by an embryo sporophyte. 188. Cyciic: applied to an arrangement of leaves or floral parts in which two or more appear upon the axis at the same level, forming a cycle, or whorl, or verticil. 159. DeuiscENnce: the opening of an organ to discharge its contents, as in sporangia, pollen-sacs, capsules, ete. 199. Dicuotomous: applied to a style of branching in which the tip of the axis forks. 35. Diacious: applied to plants in which the two sex-organs are upon dif- ferent individuals. 115. DorsiventRAL: applied to a body whose two surfaces are differently exposed, as an ordinary thallus or leaf. 109. Eee: the female gamete. 16. Eac-apparatus : in Angiosperms the group of three cells in the embryo- sac composed of the egg and the two synergids. 204. Exater: in Liverworts a spore-mother-cell peculiarly modified to aid in scattering the spores. 103. Empryo: a plant in the earliest stages of its development from the spore. 187. Empryo-sac: the megaspore of Spermatophytes, which later contains the embryo. 178. EyposprrM : the nourishing tissue developed within the embryo-sac, and thought to represent the female gametophyte. 180. ENposPeRM NUCLEUS: the nucleus of the embryo-sac which gives rise to the endosperm. 205. EntomopiiLous : applied to flowers or plants which use insects as agents of pollination. 196. GLOSSARY 331 Epieynovs: applied to a flower whose outer parts appear to arise from the top of the ovary, 225. Evsporanerate: applied to those Pteridophytes and Spermatophytes whose sporangia develop from a group of epidermal and deeper cells, 157. Famity: a group of related plants, usually comprising several genera. 236. Fervinizatioy : the union of sperm and egg. 16. FILAMENT: the stalk-like part of a stamen. 197. Fission: cell-division which includes the wall of the old cell. 10. Foor: in Bryophytes the part of the sporogonium imbedded in the gametophore; in Pteridophytes an organ of the sporophyte embryo to absorb from the gametophyte. 98, 188, GAMETANGIUM: the organ within which gametes are produced. 11. GAMETE: a sexual cell, which by union with another produces a sexual spore. 10. GAMETOPHORE: a special branch which bears sex organs. 98, GAMETOPHYTE: in alternation of generations, the generation which bears the sex organs. 97. GENERATIVE CELL: in Spermatophytes the cell of the male gameto- phyte (within the pollen grain) which gives rise to the male cells. 180. Genvs: a group of very closely related plants, usually comprising sev- eral species. 237. Havsroricm: a special organ of w parasite (usually a fungus) for ab- sorption. 50. Herrerogamovs: applied to plants whose pairing gametes are un- like. 15. Hererosporots : applied to those higher plants whose sporophyte pro- duces two forms of asexual spores. 151. Ilomosporous: applied to those plants whose sporophyte produces simi- lar asexual spores. 151. Host: a plant or animal attacked by a parasite. 48. Hypua: an individual filament of a mycelium. 49. Hypocoryn: the axis of the embryo sporophyte between the root-tip and the cotyledons. 209. Hyrpoernovs : applied to a flower whose outer parts arise from beneath the ovary. 224. 832 GLOSSARY Inpustum : in Ferns a flap-like membrane protecting a sorus. 148. INFLORESCENCE: a flowet-cluster. 280. Insertion: the point of origin of an organ, 224. InteGuMENT: in Spermatophytes a membrane investing the nucellus. 178. InvoLucre: a cycle or rosette of bracts beneath a flower-cluster, as in Umbellifers and Composites. 275. Isocarpic: applied to a flower whose carpels equal in number the other floral organs. 268. Isocamous: applied to plants whose pairing gametes are similar, 15. LEPTOSPORANGIATE: applied to those Ferns whose sporangia develop from a single epidermal cell. 157. MALe cEL.: in Spermatophytes the fertilizing cell conducted by the pollen-tube to the egg. 180. MrGaAsporRANGIuM: asporangium which produces only megaspores. 152. Mecaspore: in heterosporous plants the large spore which produces a female gametophyte. 152. MecasporopHyLL: a sporophyll which produces only megasporangia. 152. MesopnyLi: the tissue of a leaf between the two epidermal layers which usually contains chloroplasts. 141. MIcROSPORANGIUM: a sporangium which produces only microspores. 152. Microspore: in heterosporous plants the small spore which produces a male gametophyte. 152. MicRosPoROPHYLL : a sporophyll which produces only microsporangia. 152. MicropyLe: the passageway to the nucellus left by the integument. 178. Monacrous: applied to plants in which the two sex organs are upon the same individual. 115. MonopopiaL: applied to a style of branching in which the branches arise from the side of the axis. 35. Moruer ceLn: usually a cell which produces new cells by internal divi- sion. 9. Mycretium: the mat of filaments which composes the working body of afungus. 49. NAKED FLOWER: one with no floral leaves. 222. Nucenuus: the main body of the ovule. 178. GLOSSARY 333 Ooco1um : the female, egg-producing organ of Thallophytes. 16. OospHERE: the female gamete, or egg. 16. OosporE: the sexual spore resulting from fertilization. 16. Ovary: in Angiosperms the bulbous part of the pistil, which contains the ovules, 199. OvuLE: the megasporangium of Spermatophytes. 178. Pappus : the modified calyx of the Composites. 278. PaRasiTE: a plant which obtains food by attacking living plants or ani- mals. 48. PeEnTAcycLic : applied to a flower whose four floral organs are in five cycles, the stamens being in two cycles. 268. Perianru: the set of floral leaves when not differentiated into calyx and corolla. 221. Pericynous: applied to a flower whose outer parts arise from a cup surrounding the ovary. 225, Peta: one of the floral leaves which make up the corolla. 221. PnotosynrueEsis: the process by which chloroplasts, aided by light, manufacture carbohydrates from carbon dioxide and water. 84. Pisin: the central organ of the flower, composed of one or more car- pels. 200. PIsTILLATE : applied to flowers with carpels but no stamens. 218. PoLLen : the microspores of Spermatophytes. 174. PoLLEN-TUBE: the tube developed from the wall of the pollen grain which penetrates to the egg and conducts the male cells. 180. PoLLination: the transfer of pollen from anther to ovule (in Gymno- sperms) or stigma (in Angiosperms). 181. PoLyPETALous: applied to flowers whose petals are free from one an- other. 227. ProtHaLLium : the gametophyte of Ferns. 130. ProtoxemMa: the thallus portion of the gametophyte of Mosses. 98. Raprau; applied to a body with uniform exposure of surface, and pro- ducing similar organs about a common center. 120. RecepracLe: in Angiosperms that part of the stem which is more or less modified to support the parts of the flower. 222. Rauizor : a hair-like process developed by the lower plants and by inde- pendent gametophytes to act as a holdfast or absorbing organ, or both. 109. SaPROPHYTE: a plant which obtains food from the dead bodies or body products of plants or animals. 48. 334 GLOSSARY ScaLe: a leaf without chlorophyll, and usually reduced in size. 161. SEpaL: one of the floral leaves which make up the calyx. 221. Seta: in Bryophytes the stalk-like portion of the sporogonium. 98. SEXUAL sPoRE: one produced by the union of gametes. 10. SpeciEs : plants so nearly alike that they all might have come from a single parent. 287. Sperm: the male gamete. 16. SPIRAL: applied to an arrangement of leaves or floral parts in which no two appear upon the axis at the same level; often called alter- nate. 193. Sporaneium: the organ within which asexual spores are produced (ex- cept in Bryophytes). 10. Spore: a cell set apart for reproduction. 9. Sporocontum : the leafless sporophyte of Bryophytes. 98, SPoROPHORE : a special branch bearing asexual spores. 49. SpoROPHYLL: a leaf set apart to produce sporangia. 145. Sporopuyre: in alternation of generations, the generation which pro- duces the asexual spores. 97. Sramen: the microsporophyll of Spermatophytes. 174. STAMINATE: applied to a flower with stamens but no carpels. 218. Sriema: in Angiosperms that portion of the carpel (usually of the style) prepared to receive pollen. 199. Stroma (pl. Stomava): an epidermal organ for regulating the communi- cation between green tissue and the air. 141. Srropiius: a cone-like cluster of sporophylls. 161. SryLe: the stalk-like prolongation from the ovary which bears the stigma, 199. Suspensor : in heterosporous plants an organ of the sporophyte embryo which places it in a more favorable position in reference to food supply. 168. SyMBIoNT: an organism which enters into the condition of symbio- sis. 79. Symprosts: usually applied to the condition in which two different organisms live together in intimate and mutually helpful rela- tions, 7. Symprratous: applied to a flower whose petals have coalesced. 227, Syncarpous: applied to a flower whose carpels have coalesced. 226. Synerei : in Angiosperms one of the pair of cells associated with the egg to form the egg-apparatus. 204. GLOSSARY 335 Testa: the hard coat of the seed. 184. TETRACYCLIc: applied to a flower whose four floral organs are in four cycles. 268. TETRAD: a group of four spores produced by a mother-cell. 103. ZoosPorE : a motile asexual spore. 10. ZyGomorPuic: applied to a fluwer in which the parts in one or more sets are not similar; irregular, 229. ZyGore: the sexual spore resulting from conjugation. 15. INDEX TO PLANT STRUCTURES [The italicized numbers indicate that the subject is illustrated upon the page cited. In such case the subject may be referred to only in the illustration, or it may be referred to also in the text.] A Absorption, 299. Acacia, 265. Aconitum, 261. Acorus, 219, 248. Actinomorphy, 228. Adder’s tongue : see Ophioglossuin, Adiantum, 148, 145. ZEicidiomycetes, 50, 62. AXicidiospore, 66. ZXcidium, 66. Agaricus, 68, 69. Agave, 247. Air pore: see Stoma. Akene, 212, 213, 214, 276, 277. Alchemilla, 275. Alder: see Alnus, Algw, 4, 5, 17. Alisma, 210, 240. Almond: see Prunus. Alnus, 257, Alternation of generations, 94, 129. Amanita, 70. Amaryllidacex, 247, Amaryllis family: see Amarylli- dace. Ambrosia, 279. Ament, 257. Anaptychia, 87, 82, Anemophilous, 181. Angiosperms, 178, 195, 217. Anisocarpx, 268. Annulus, 136, 146, 150. Anther, 196, 197, 199. Antheridium, 16, 99, 100, 112, 121, 133, 134, 161, 166. Antherozoid, 16. Anthoceros, 104, 105, 111, 116, 118. Anthophytes, 172. Antipodal cells, 202, 205, 208. Antirrhinum, 228, 275. Ant-plants, 90, 92. Apical cell, 234. Apical group, 283. Apium, 267. Apocarpy, 199, 222, 225. Apocynacee, 271, Apocynum, 272, Apogamy, 1381, Apospory, 182. Apothecium, 79, 81, 82. Apple: see Pirus. Aquilegia, 198. Aracer, 243, Araliacez, 267. Araucaria, 190. Arbor vite: see Thuja. Arbutus, 198: see Epigea, Archegoniates, 101. 337 338 Archegonium, 99, 100, 713, 114, 133, 185, 161, 167, 179. Archesporium, 102, 104, 105, 146. Archichlamydew, 255. Arctostaphylos, 269. Areolie, 111, 114. Ariswma, 248, 244. Arnica, 275, 276, 278. Aroids, 248. Artemisia, 279. Arum, 245. Ascocarp, 58, 59. Ascomycetes, 50, 57. Ascospore, 59. Ascus, 59. Asexual spore, 9. Aspidium, 180, 16, 144. Assimilation, 302. Aster, 279. Astragalus, 265. Atherosperma, 198. Azalea, 270. B Bacillus, 76. Bacteria, 21, 75. 76. Balm: see Melissa. Banana, 140. Bark, 284, 289. Basidiomycetes, 50, 68 Basidiospore, 6.9, 72. Basidium, 69, 71. Bean: see Phaseolus. Bearberry: see Arctostaphylos. Beech, 256. Bellis, 279. Berberis, 798. Bidens, 278. Beggar-ticks, 213. Bignonia, 211. Birch, 256. Blackberry: see Rubus. INDEX Black knot, 60. Black mould, 52. Blasia, 116. Blueberry: see Vaccinium. Blue-green alge, 6, 17. Blue mould, 60. Boletus, 73, 74. Botrychium, 145, 749. Botrydium, 28. Box elder, 234. Bracket fungus, 72. Brake: see Pteris. Brassica, 261. Bryophytes, 2, 98, 172. Brown alge, 6, 32. Bryum, 720, 124. Buckeye, 235. Butomus, 199. Buttercup: see Ranunculus. Buttercup family: see Ranuncu- lacea. C Cabbage: see Brassica. Calamus: see Acorus. Calla-lily, 248. Callithamnion, 43. Callophyllis, 39. Calluna, 270. Calopogon, 249. Caltha, 260. Calycanthus, 220, 261. Calypso, 24. Calyptra, 102, 125. Calyptrogen, 293, Calis, 220 27s Cambium, 285, 287, 288. Capsella, 209, 29:3. Capsule, 98, 123, 125, 126, 211, 212. Caraway: sce Carum, Carbohydrate, 3802. Carbon dioxide, 83. Carnivorous plants, 92. Carpel, 177, 178, 199, 219, 220. Carpinus, 217, 258. Carpospore, 44, 45. Carrot: see Daucus, Carum, 267. Cassia, 265, Cassiope, U9, Castilleia, 275, Catkin, 257. Catnip: see Nepeta. Cat-tail: see Typha. Cattleya, 254. Cuulicle, 209, Cauline, 166. Cedar apple, 67, 68. Celery: see Apium. Cell, 6, 7. Cellulose, 7. Cercis, 265. Chalazogamy, 258, 259, Characew, 46. Chemotropism, 307. Cherry: see Prunus. Chestnut, 256, Chlorophycee, 6, 21. Chlorophyll, 5, 88. Chloroplast, 7, 8. Chrysanthemum, 279. Cilia, 10. Circinate, 736, 143. Cladophora, 25. Clavaria, 72. Climbing fern: see Lygodium. Closed bundle, 290. Clover: see Trifolium. Club mosses, 162. Cnicus, 278. Cocklebur: see Xanthium. Cenocyte, 27. Coleochete, 106, 707. Collateral bundle, 287, INDEX 339 Collenchyma, 284. Columella, 104, 105, 106, 126 Compass plant: see Silphium, Composite, 275. Composites, 275, 276, 277, 278. Concentric bundle, 292. Conferva forms, 22. Conidia, 58, 60. Conifers, 191, 282. Conium, 267. Conjugate forms, 31. Conjugation, 15. Connective, 196. Conocephalus, 111. Convolvulacew, 271. Conyvolvulus forms, 270. Convolyulus, 272, Coprinus, 7”. Coral fungus, 73, 74. Coreopsis, 278. Coriandrum, 267. Cork, 284. Corn, 216, 28.2, 290. Cornacee, 267. Corolla, 22u, 221. Cortex, 285, 284, 288. Cotton, 206. Cotyledon, 737, 188, 168, 184, 209, 1 dl. OL Cranberry: see Vaccinium. Crategus, 262. Crocus, 249, Crucifer, 262. Cruciferae, 262. Cryptogams, 172. Cunila, 274. Cup fungus, 60, 62. Cupule, 722, 114. Cyanophycee, 6, 17. Cycads, 185, 186, 187, 189. Cyclic, 159, 193. Cyperacee, 241, 840 Cypripedium, 249, 253. Cystocarp, 48, 44.0 Cystopteris, 7s, 144. Cytoplasm, 7. D Daisy: see Bellis. Dandelion: see Taraxacum. Dasya, 40. Datura, 197. Daucus, 266, 267. Dead-nettle, 228. Definitive nucleus: see Endosperm nucleus. Dehiscence, 198, 199. Delphinium, 260, 261. Dermatogen, 283. Desmids, 81, 32. Desmodium, 308. Diatoms, 45. Dichotomous, 35. Dicotyledons, 208, 288, 254, 282. Differentiation, 3, 280. Dogbane: see Apocynum. Dog-tooth violet: see Erythronium. Dogwood family: see Cornace. Dorsiventral, 109. Downy mildew, 55. Drupe, 264. Digestion, 302. Dicecious, 115, Disk, 276, 277. Dodder, 86. E Ear-fungus, 74. Easter lily, 2:27. Ecology, 297, 311. Economic botany, 297. Ectocarpus, 33. Edogonium, 22, 23. Egg, 16, 202, 204, 205, 206. INDEX Egg-apparatus, 204, 205, 206. Elater, 103, 123, 118. Elm: see Ulmus. Embryo, 137, 167, 168,170, 183, 207, 208, 209, 210, 211. Embryo-sac, 178, 179, 201, 205, 208. Endosperm, 179, 180, 207, 208, 211. Endosperm nucleus, 202, 205. Entomophilous, 196. Epidermis, 141, 142, 191, 288, 284, 295. Epigwa, 269. Epigyny, 224, 228. Kpilobium, 212. Epiphyte, 157. Equisetales, 159. Equisetum, 159, 260, 261. Ergot, 60, 62. Erica, 270. Ericacer, 268. Erigenia, 267. Krythronium, 250. Eusporangiate, 157. Evolution, 3. F Fennel: see Foeniculum. Ferns, 155, 156. Fertilization, 16, 181, 206, 207. Festuca, 240. Figwort family: see Scrophula- riacer. Filament, 8, 796, 197. Filicales, 155. Fireweed: see Epilobium. Fission, 10. Flax: see Linum. Floral leaves, 218, Floridee, 38. Flower, 218. Flowering plants, 172. Feeniculum, 267. INDEX Foliar, 166. Food, 83, 299. Foot, 98, 1202, 137, 138, 168. Fragaria, 14, 2.77, 262. Fruit, 211, 222, 213, 214, 215 Fucus, 03, 37. Funaria, 99, 102, 121, 124, 125, 120. Fungi, 4, 48. G Gametangium, 11. Gamete, 10, 12. Gametophore, 9%, 172, 120, 124. Gametophyte, 97, 107, 182, 134, 162. 166, 167, 176, 179, 180, 201, v8, 204, 205. Gaultheria, 270. Gaylussacia, 260. Gemma, 112, 114. Generative cell, 180, 201. Gentianacex, 271. Geophilous, 246. Geotropism, 305. Gerardia, 275. Germination, 187, 214. Gigartina, 38. Gills, 71. Ginkgo, 191. Gladiolus, 249, 257. Gleditschia, 236, 265. Gleocapsa, 17, 18. Glume, 241. Goldenrod: see Solidago. Gonatonema, 31. Graminee, 241. Green alge, 6. 21. Green plants, 88. Green slimes, 20. Grimmia, 176. Growth movement, 304, Growth ring, 234, Grain, 241. 40 Grasses, 240. Grass family: see Graminee. Gymnosperms, 171, 178, 195. Gymnosporangium, 7, H Habenaria, 249, 252. Harebell, 7/8. Haustoria, 50. Hazel: see oo Heart-wood, 28 Heat, 314. ' Heath family: see Ericacez. Heaths, 268, 269, 27 Helianthus, 279, 283, 306. Heliotropism, 305. Hemiarcyria, 75. Hemlock: see Conium. Henbane: see Hyoscyamus. Hepatic, 109. Heterocyst, 18. Heterogamy, 15. Heterospory, 151, Hickory, 256, Hippuris, 283, Homospory, 151. Honey locust: see Gleditschia. Horehound: see Marrubium. Hornbeam : see Carpinus. Horsetail, 159. Host, 48. Huckleberry: see Gaylussacia. Hydnum, 73, 74. Hydra, 90. Hydrophytes. 6, 315. Hydrophytum, 91. Hydrotropism, 307. Hygroscopie movement, 304. Hyoseyamus, 156. Hypha, 49. Hypocotyl, 184, 209, 216, 217. 342 Hypodermis, 284. Hypogyny, 224, 225. Hyssopus, 274. i Indigo: see Indigofera. Indigofera, 265. Indusium, 136, 148, 144. Inflorescence, 230. Insects and flowers, 90. Integument, 178, 179, 201, 202, 208. Involucre, 267, 275, 277. Ipomoea, 228, 270. Tridacew, 247. Tris, 248, 251. Iris family: see Iridacee, Irritable mavement, 307. Isocarpa, 268. Isoetes, 169. Isogamy, 15. Japan lily, 248. Jungermannia, 105, 115, 226, 117. Juniper, 194. k Kalmia, 270. Labiate, 272. Lahiates, 272. Lactuca, 279. Laminaria, 88, 34. Lamium, 274, 275. Larch: see Larix. Larix, 192. Larkspur: see Delphinium. Laurel: see Kalmia. Lavandula, 275. Leaf, 141, 142, 295, 296, 811. Legumes, 250, 251, 264. INDEX Leguminose, 264, Lemna, U1. Lepidozia, 127. Leptosporangiate, 157, Lettuce: see Lactuca. Leucanthemum, 279. Liatris, 278. Lichens, 77, 78, 79, 87. Life relations, 311. Light, 314. Ligule, 168, Liliacew, 246. Lilies, 245. Lilium, 203, 204, 205, 207, 224, 249, 295. Lily: see Lilium. Lily family: see Liliacez. Linaria, 228, 275. Linum, 220. Liverworts, 109. Loculus, 200. Locust: see Robinia. Lotus, 204. Lupinus, 265. Lycopersicum, 275. Lycopodiales, 162. Lycopodium, 162, 763. Lygodium, 145, Lyonia, 269. M Macrospore, 152. Maidenhair fern: see Adiantum. Male cell, 180, 187, 201, 206, 207. Maple, 272. Marasmius, 7. Marchantia, 704, 110, 271, 112, 113, 11h. Marguerite: see Leucanthemum. Marjoram : see Origanum., Marrubium, 275. Marsh marigold: see Caltha, INDEX. Marsilia, 158. Megasporangium, 152, 177, 170. Megaspore, 152, 165, 167, 179, 201, BOS Megasporophyll, 152, 165, 177, 199. Melissa, 275. Mentha, 229, 274. Meristem, 281. Mesophyll, 141, 142, 191, 295. Mesophytes, 324. Mestome, 282. Micropyle, 178, 201, 20.2, 200. Microspira, 76. Microsphera, 58. Microsporangium, 152, 176, 197. Microspore, 152. 165, 166, 779, 197. 201. Microsporophyll, 152, 165, 174, 196, 198. Midrib, 234. Mildews, 57. Mimosa, 265, 308, 309. Mint: see Mentha. Mint family: see Labiate. Monocotyledons, 208, 252, 286, 280, Moneecious, 115. Monopodial, 35. Monotropa, 270. Moonwort: see Botrychium. Morels, 60, 6? Morning-glory: see Ipomeea. Morphology, 247. Mosses, 98, 119, 124. Mother cell, 9. Mougeotia, 31. Movement, 303. Mucor, 49, 52, 53, 54, 58. Mullein: see Verbascum. Musci, 119. Mushrooms, 68. Mustard family: Mycelium, 49. see Crucifere. 343 Mycomycetes, 50, Mycorrhiza, 87, 88. Myristica, 214. Myrmecophytes. 90, 92. Myxomycetes, 74, 75. N Naias, 237. Narcissus, 247. Nemalion, 42. Nepeta, 275. Nicotiana, 227, 275. Nightshade family : see Solanacee, Nostoe, 18. Nueellus, 178, 179, 2v1, Nucleus, 7 202, 03. ' Nutation, 304, Nutmeg, 21}. Nutrition, 3, 299. Nyctitropic movement, 309. Nympheacee, 261. O Oak, 255, 256. (Edogonium: see Edogonium. Onoclea, 145, 147, 148. Oogonium, 16. Oosphere, 16. Oospore, 16, 101. Open bundle, 287. Operculum, 122, 125. Ophioglossum, 145, 249. Orchidacee, 249. Orchids; 249; 752.253. 254. Orchid family: see Orchidacex. Origanum, 274. Ornithogalum, 247. Oscillaria, 29. Osmunda, 145. 156. Ostrich fern: see Onoclea, Ona 299, 200: 202, Ovule, 178, 179, 201, 203. 344 P Palisade tissue, 742, 295. Palmacer, 241. Palm family: see Palmacew. Palms, 241, 242, 243. Papaveraceex, 261. Pappus, 270, 277, 278. Parasites, 48, 85. Parenchyma, 280, 281, 282, 288. Parmelia, 70. Parsley: see Petroselinum. Parsley family: see Umbelliferw. Parsnip: see Pastinaca. Parthenogenesis, 52. Pastinaca, 267. Pathology, 297. Pea: see Pisum. Peach: see Prunus. Peach curl, 60. Pea family: see Leguminose. Pear: see Pirus. Peat, 119. Pellewa, 146. Penicillium, 60. Pentacycle, 268. Pentstemon, 275. Peony, 20. Pepper, /17, 258. Pepper family: see Piperacee. Perianth, 219, 22, 221. Periblem, 282. Perigyny, 225, 220. Peristome, 16, 127. Peronospora, 55, 56. Petal, 220, 221. Petiole. 141. Petroselinum, 267. Phieophycew, 6, 32. Phanerogams, 172. Phaseolus, 216, 265. Phloem, 286, 287, 288, 290, 20.2, 204 INDEX Phlox, 228, 271. Photosyntax, 84. Photosynthesis, 84, 302. Phycomycetes, 50, 51. Physcia, 79. Physiology, 297. Picea, 179, 181, 18. Pileus, 71. Pine: see Pinus. Pineapple, 215. Pinus, 173, 175, 176, 177, 178, 181, 183, IN4, ISS, 101, 280. Piperaces, 258. Pirus, 225, 262, 263. Pistil, 199, 200, 219, 220. Pisum, 265. Pith, 285, 287, 288. Planococeus, 74. Plantaginacee, 275. Plant body, 6. Plant societies, 313. Plasmodium, 74, 75. Plastid, 7, 8. Platycerium, 132. Plerome, 283. Pleurococeus, 21. Plum: see Prunus. Plumule, 210. Pod, 211, 212. Pogonia, 249. Polemoniacee, 271. Polemonium, 271. Pollen, 174, 176, 197, 201. Pollen-tube, 779, 180, 181, 187, 202, 206, 207. Pollination, 181. Polyembryony, 183. Polymorphism, 63. Polypetaly, 226. Polyporus, 71, 7.2. Polysiphonia, #4. Polytrichum, 96, INDEX Pome, 268. Pondweeds, 237. Poplars, 255. Popowia, 188. Poppy, 261. Poppy family: see Papaveracee. Populus, 256. Pore-fungus, 72. Potamogeton, 237, 238. Potato: see Solanum. Potentilla, 2/5, 262. Proteid, 302. Prothallium, 130, 132, 1/4. Protococcus forms, 22. Protonema, 95, 98. Protoplasm, 7. Prunus, 71.', 262. Pseudomonas, 76. Pseudopodium, 105, 123, 124. Pteridophytes, 2, 128, 172, 201. Pteris, 133, 134, 135, 187, 141, 142, 148, 145, 281, 291, 292, 298. Ptilota, 42. Puccinia, 63, 64, 65, 66. Puff-balls, 68, 74. Pulvinus, 308. Q Quillwort: see Isoetes. R Rabdonia, 41. Radiate bundle, 294. Radicle, 209. Radish, 120. Ragweed: see Ambrosia. Ranunculacee, 261. Ranunculus, 222, 259. Raspberry: see Rubus. Rays, 275, 276. Receptacle, 222. Red alge, 6, 38. Redbud : see Cercis. Redwood: see Sequoia. Reproduction, 3. 8. 309, Respiration, 302. Rheotropism, 307, Rhizoid, 109, 170, 134. Rhizophores, 164. Rhododendron, 270, 271. Rhodophycee, 6, 3%, Riccia, 104, 110. Ricciocarpus. 110. Ricinus. 288, Robinia, 265. Root, 138. 217, 298, 294, 818. Root-cap, 29.2. Root-fungus, 87. 88. Root-hairs, 217, 300. Root-pressure, 300. Root-tubereles, $9. Rosacew, 262. Rose family: see Rosacew. Rosin-weed: see Silphium. Rosmarinus, 275. Royal fern: see Osmunda. Rubus, 202. Rumex, 284. Rust, 62, 63, 64. 65, 66. Ss Sac-fungi, 57. Sage: see Salvia. Sage-brush: see Artemisia. Sagittaria, 208, 388. Salix, 219, 233, 256, 257. Salvia, 275. Salvinia, 158. Saprolegnia, 51. 52. Saprophyte, 48, 84. Sap-wood, 289. Sargassum, 35, 36. Saururus, 229, 258. Seales, 161. 346 Scapania, 116. Schizomycetes, 21. Schizophytes, 21. Sclerenchyma, 281, 282, 284, 255, 288, 290, 201. Scouring rush, 159. Onn Scrophulariacee, 275. Scutellaria, 275. Sedge family: see Cyperacee. Seed, 183, 284, 210, 211, 212, 214. Selaginella, 162, 264, 105, 100, 168. Sensitive fern: see Onoclea. Sensitive-plant: see Acacia. Sepal, 220, 221. Sequoia, 289. Seta, 98, 125. Sex, 12. Sexual spore, 10. Shepherd’s purse: see Capsella. Shield fern: see Aspidium. Shoot, 812. Sieve vessels, 285, 286. Silphium, 279. Siphon forms, 27. Siphonogams, 183. Siphonogamy, 183. Slime moulds, 74, 75. pt, 62: Snapdragon: see Antirrhinum. Soil, 314. Solanacew, 275. Solanum, 798, 275. Solidago, 279. Solomon’s seal, 2.3.3. Sorus, 196, 143, 144. Spadix, 244, 245. Spathe, 244, 245. Sperm, 16, 100, 7.33, 169, 187, 190. Spermatia, 43, 44, Spermatophytes, 2, 171, 172. Spermatozoid, 16. 35, 162, 166, INDEX Sperm mother cell, 100. Sphagnum, 105, 106, 122, 123. Spike, 240. Spirea, 262. Spiral, 193. Spirillum, 76. Spirogyra, 28, 29, 30. Spongy tissue, 142. Sporangium, 10, 136, 148, 145, 150, 157, 163, 179. Spore, 9. Sporidium, 65. Sporogenous tissue, 103. Sporogonium, 98, 102, 104, 105, 106, Ls, doe. Sporophore, 49, 50. Sporophyll, 145, 247, 148, 149, 174, 176. Sporophyte, 97, 102, 137, Spruce: see Picea. Stability of form, 298. Stamen, 174, 176, 196, 198, 219, 220. Stele, 191, 288, 285. Stem, 189, 282, 289, 291, 312. Stemonitis, 75. Stereome, 282, 299. Sterile tissue, 103. Sticta, 80. Stigma, 199, 202. Stomata, 141, 142, 191, 295, 301. Strawberry: see Fragaria. Strobilus, 160, 161, 163, 165, 174, 175, 106, 198, 14. Style, 109, 202. Substratum, 49. Sumach, 225, Sunflower: see Helianthus. Suspensor, 107, 168, 183, 210. Symbiont, 79, 86. Symbiosis, 79, 86. 209, Sympetale, 268. Sympetaly, 226, 227. Symplocarpus, 243. Synearpy, 199, 219, 225, Synergid, 2u2, 204, 205, 2uc. E, Tanacetum, 279. Tansy: see Tanacetum. Taraxacum, 210, 277, 278. Taxonomy, 207. Teleutospore, 64, 68. Tension of tissues, 298. Testa, 184, 211. Tetracyclie, 268, Tetrad, 103. Tetraspore, 43. Teucrium, 230, 274, 275. Thallophytes, 2, 4, 172. Thermotropism, 307. Thistle: see Cnicus. Thorn apple: see Datura. Thuja, 192. Thymus, 274. Tickseed: see Coreopsis. Tissues, 280. Toad-flax: see Linaria. Toadstools, 68. Tobacco: see Nicotiana. Tomato: see Lycopersicum. Trachew, 285, 286. Tracheids, 286. Transfer of water, 300. Transpiration, 301. Tree fern, 140. Trichia, 75. Trichogyne, 43, 44. Trillium, 207, 246, 265. Truffles, 60. Turgidity, 298. Typha, 239, 240. INDEX 347 U Umbel, 266, 267. Umbelliferee, 266, Umbellifers, 266. Ulmus, 710, 256. Ulothrix, 12, 13, 22. Uredo, 64. Uredospore, 63, 64, Vv Vaccinium, 269. Vascular bundle, 22.2, 23.4, 287, 291. Vascuiar cylinder, 234, 287. Vascular system, 129, 139. Vaucheria, 26, 27, 28. Vegetative multiplication, 9. Veins, 141, 142. Venation, 233. Verbaseum, 275. Verbenacer, 275, Vernation, 143. Vernonia, 279. Veronica, 275, Vicia, 265. Violet, 211, 229. WwW Wall cell, 180. Walnut, 256. Water, 83, 314. Water ferns, 158. Water-lily, 223, 261. Water-lily family: see Nymphea- cer. Water moulds, 51. Wheat rust, 63, 64, 65, 66. Willow: see Salix. Wind, 315. Wintergreen: see Gaultheria. 348 INDEX Wistaria, 265. Y Witches’-broom, 60. Yeast, 62. Wormwood: see Artemisia. Z Zannichellia, 237. Xx Zoospore, 10. Xanthium, 279. Zygomorphy, 228, 229. Xerophytes, 319. Zygospore, 15. Xylem, 285, 287, 288, 290, 292, 294. | Zygote, 15. THE END TWENTIETH CENTURY TEXT-BOOKS. NOW_ READY. Plant Relations. 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