Plant studies; an elementary botany

Front matter

es

: aetansirarontenesareat a aS

New York

Preface

Tu1s book has been prepared in response to the earnest solicitation of those schools in which there is not a sufficient allotment of time to permit the development of plant ecology and morphology, as outlined in Plant Relations and Plant Structures; and yet which are desirous of imparting instruction from both points of view. To meet this need, the essential portions of the two books referred to have been selected and combined, which, with the addition of some new matter to give it logical continuity and a degree of completeness, have been organized into this volume under the title of Plant Studies.

The book falls naturally into two divisions, the first fourteen chapters being dominated by Ecology, and representing the view point of Plant Relations. The remaining eleven chapters are dominated by Morphology, and present in much simpler form, especially in the higher groups, the ideas of Plant Structures. While the author believes that these two regions of the book are put in proper sequence for elementary instruction, he is very far from seeking to impose such an opinion upon teachers, who must use a sequence adapted to their own convictions and material. Hence many may prefer to begin with Chapter XV, and return to the preceding chapters later; or, what is perhaps vi PLANT STUDIES better, they may prefer to combine the two divisions of the book much more intimately.

In any event, the book is not a laboratory guide, or a book merely for recitation, but is for reading and study in connection with laboratory and field-work. The intention is to present a connected, readable account of some of the fundamental facts of botany, and to give a certain amount of information. If it performs no other service in the schools, however, its purpose 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 supplement to three far more important 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 structures; (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 factors, the book seeks to organize them, and to suggest explanations. It seeks to do this in two ways: (1) by means of the text, which is intended to be clear and untechnical, but compact; (2) by means of the illustrations, which must be studied as carefully as the text, as they are only second in importance to the actual material. Especially is this true in reference to the landscapes, many of which can not be made a part of experience.

My thanks are due to various members of the Department of Botany of the university for preparing and selecting illustrations. The illustrations of the first fourteen

PREFACE vii chapters were under the general direction of Dr. Henry C. Cowles, while those of the remaining chapters were provided by Dr. Otis W. Caldwell. In this work Dr. Caldwell had the very efficient assistance of S. M. Coulter, B. A. Goldberger, J. G. Land, and A. C. Moore, whose names appear in connection with the drawings they furnished. Grateful acknowledgment should also be made to Dr. W. J. Beal, whose little book entitled Seed Dispersal furnished several illustrations; and to Professor George F. Atkinson, whose excellently illustrated Hlementary Botany performed a like service. Both of these authors are credited in connection with the illustrations used from their works. The fine illustrations from Kerner and from Schimper, and from other authors, will also be recognized; but their names will all be found in the legends.

JoHN M. Courter.

Tue University or Carcaco, June, 1900.

Preface To The Revised Edition

Durine the last four years the science of Botany has made rapid progress, both in the addition of new facts and in changed points of view. Some of this progress affects Plant Studies, and it is recorded in this revised edition so far as it can be without a complete rewriting of the volume. Changes will be found, therefore, in statements of fact, in points of view, in terminology, in illus. trations, and also in the addition of new material.

Joun M. CouLrer.

Tue University oF Cuicago, April, 1904.

CHAPTER I.—IntTRoDUCTION . : : : F

I].—Fo.LtaGE LEAVES: THE LIGHT RELATION . ; 7 , TII.—Fo.iaGE LEAVES: FUNCTION, STRUCTURE, AND PROTECTION IV.—SuHoots

V.—Roots

VI.—REPRODUCTIVE ORGANS

VII.—FLOWERS AND INSECTS F

VIII.—AN INDIVIDUAL PLANT IN ALL OF ITS RELATIONS IX.—THE STRUGGLE FOR EXISTENCE.

X.—THE NUTRITION OF PLANTS 3 3 XI.—PLanT ASSOCIATIONS: EcoLOGICAL FACTORS

XII.—HypDROPHYTE ASSOCIATIONS ; ‘

XIII.—XeERoPHYTE ASSOCIATIONS . : :

XIV.—MESOPHYTE ASSOCIATIONS . A

XV.—THE PLANT GROUPS . : - : A , ‘ XVI.—THALLOPHYTES: ALGE . . : : : : XVII.—THE GREAT GROUPS OF ALGE . : : ‘ XVIII.—THaLLopHytEs: Funer . ‘ : 5 ‘ F XIX.—BRYOPHYTES (MOSS PLANTS) : : H ; $ XX.—THE GREAT GROUPS OF BRYOPHYTES ‘: 4 ‘

XXI.—PTERIDOPHYTES (FERN PLANTS) . : : : :

XXII.—Tue GREAT GROUPS OF PTERIDOPHYTES . ‘ P

XXIII.—SpPERMATOPHYTES: GYMNOSPERMS . A . A

XXIV.—SpPERMATOPHYTES: ANGIOSPERMS ; = * °

XXV.—MonocotyLepons anD DicoTyLEDOoNS . : ‘ GLOSSARY . F ‘ . : ; ‘ 5

23 OVE A NOY

CoA Ss bes

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 (al/g@) found in water.

2. Plant associations.—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, etc. In this way the general appearance of vegetation is exceedingly varied, and each appearance tells of certain conditions of living. These groups of plants living together in similar conditions, as trees and other plants in a forest, or grasses and other plants in a meadow, are known as plant associations. These 1 associations are as numerous as are the conditions of living, and it may be said that each association has its own special regulations, which admit certain plants and exclude others. The study of plant associations 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 associations, 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 ag 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 certain 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 (alg@), 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 as root, stem, leaf, and flower (see Figs. 75, 144, 161, 169). The plant without these special parts is said to be simple, the plant with them is called complez, The simple plant lives in the same way and does the same kind of work, so far as living is concerned, as does the complex plant. The difference 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 unlike when different 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 simplest 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 advantage it has is that every kind of work is better done. Differentiation 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 complex plant resembles the civilized community. It must be understood, however, that in the case of plants the differentiation 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 itself (reproduction). To the great work of nutrition many kinds of work contribute, and the same is true of reproduction. 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.

%. 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 itself, 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 by a great variety of things. A root, for instance, is affected by light, gravity, moisture, soil material, contact, etc. Every organ, 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 impossible, as yet, for us to explain why all 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-relations can be considered. In order to do this, it seems better 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 organ 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 introduction 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 ight; that is, such leaves are aerial rather than subterranean (see Figs. 1, 75,174). 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. 45, 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 especially with leaves. It is also evident that this green color holds some necessary relation to light, for the leaves of plants enone in the dark, as potatoes sprouting in a cellar, do not develop this color. Even when leaves have developed the green color they lose it if deprived of light, as is shown by the process of blanching celery, 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 essential life-relations of a foliage leaf is what may be called the light-relation. ‘This seems to explain satisfactorily why such leaves are not developed in a subterranean position, as are many stems and most roots, and why plants which produce them do not grow in the dark, as in caverns. The same green, and hence the same 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 conspicuously. Another indication that the green color is connected 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 conclusion is that the leaf is a special organ for the light-relation. 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. A notable illustration of this is the cactus plant, which produces no foliage leaves, but whose stem displays the leaf color.

11. An expanded organ.—Another general fact in reference 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 does demands an exposure of surface rather than thickness of body. It is but another step to say that the amount of work an 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 ight upon its upper surface. In this way more rays of light strike the leaf surface than if it stood obliquely or on edge. It is often said that leaf blades are so directed that the flat surface is at right angles to the incident rays of hght. While this may be true of horizontal 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- Fia. 1. The leaves of this plant (Ficus) are phyll), which is essential

ps tenes en ae iodo works, he ndjust:

ward, and that the leaves become more ment to light, therefore, horizontal as the stem is ascended. It is a delicate one, for will also be seen that the leaves are go 3 broad that there are few vertical rows. there must be just enough 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 a way of protecting themselves from too intense light by their structure, rather than by a change in their position. It is evident, therefore, that the exact position which any particular leaf holds in relation to light 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 prove to be, 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 growing 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.

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, 3a, 36, 4). Some of the common house plants show this power. in the case of the common Ovalis the night

Fic. 3a. The day position of the leaves of redbud position of the leaves (Cercis).—After ARTHUR. is remarkably different from the position in light.

If such a plant is exposed to the ight 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 themselves gradually to the changed light-relations. Fie. 36. The night position of the leaves Ld; Compass plants.— A of redbud (Cercis).—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 to intense light, the leaves are turned edgewise, the flat faces being turned away from the intense rays of midday, and directed towards the rays of less intensity ; that is, those of

Fie. 4. Two sensitive plants, showing the motile leaves. 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. 170). Asa result, the plane of the leaf lies in a general north and 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 must not be supposed that there is any accuracy in the north or south direction, as the edgewise position seems to be the significant one. In the rosin-weed probably the north and south direction 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 direction of the apex (see Fig. 5).

16. Heliotropism.— The property of leaves and of other organs of responding to light is known as heliotropism, light being one of the most important of those external influences to which plant organs respond (see Figs. 6, 43).

Fie. o. The common prickly lettuce (Lactuca It should be under-

Scariola), showing the leaves standing edge- stood clearly that this wise, and in a general north and south plane. ~ Phe e —After ARTHUR and MacDovuaa.. is but a slight glimpse ara 4 Behe asin

Fic. 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 usually 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 (see Fig. 1). A relation exists, therefore, between the breadth of leaves and the number of vertical rows, and the meaning of this becomes plain when the light-relation is considered,

18. Relation of length to the distance 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 be 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 vertical 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 between them even 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 en 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 can 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 vertical rows on the stem, and the distance between the leaves

Fic. 8. A dragon-tree, showing narrow leaves extending in all directions, 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. Llongation 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 (see Fig. 9). It may be noticed that it is very common to 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 (Saintpaulia) 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 may result in a favorable relation to hght. It is a very common thing to find a plant with a cluster of comparatively large leaves at or near the base, where they are in no danger of shading other leaves, and with the stem leaves gradually becoming

FOLIAGE LEAVES: THE LIGHT-RELATION Li 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 arrangement 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 resette habit.

Often this rosette of leaves at the base, frequently lying flat on the ground or on the rocks, includes the only folage leaves the plant produces. It is evident that a rosette, in which the leaves must overlap one another more or less, is not a very favorable light arrangement, and therefore it must be that something is being

Fie. 10. A plant (Zcheveria) with fleshy provided for besides the leaves, showing large horizontal ones light-relation (see Figs. alle at base, and others pegoming smaller

: By te i and more directed upward as the 12, 13). What this is will eteinie aacended.

appear later, but even in

this comparatively unfavorable light arrangement, there is evident adjustment to secure the most light possible under the circumstances. The lowest leaves of the rosette are the longest, and the upper (or inner) ones become gradually 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 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-

Fie. 11. A group 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, and 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), asin 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.