The Elements of Botany For Beginners and For Schools

The Project Gutenberg EBook of The Elements of Botany, by Asa Gray

This eBook is for the use of anyone anywhere at no cost and with

almost no restrictions whatsoever. You may copy it, give it away or

re-use it under the terms of the Project Gutenberg License included

with this eBook or online at www.gutenberg.net

Title: The Elements of Botany

For Beginners and For Schools

Author: Asa Gray

Release Date: September 18, 2010 [EBook #33757]

Language: English

*** START OF THIS PROJECT GUTENBERG EBOOK THE ELEMENTS OF BOTANY ***

Produced by Curtis Weyant, Stephen H. Sentoff and the

Online Distributed Proofreading Team at http://www.pgdp.net

GRAY'S LESSONS IN BOTANY

REVISED EDITION

THE

ELEMENTS OF BOTANY

FOR BEGINNERS AND FOR SCHOOLS

By ASA GRAY

IVISON, BLAKEMAN, AND COMPANY

NEW YORK AND CHICAGO

Copyright,

By Asa Gray.

1887.

PREFACE.

This volume takes the place of the author's Lessons in Botany and Vegetable Physiology, published over a quarter of a century ago. It is constructed on the same lines, and is a kind of new and much revised edition of that successful work. While in some respects more extended, it is also more concise and terse than its predecessor. This should the better fit it for its purpose now that competent teachers are common. They may in many cases develop paragraphs into lectures, and fully illustrate points which are barely, but it is hoped clearly, stated. Indeed, even for those without a teacher, it may be that a condensed is better than a diffuse exposition.

The book is adapted to the higher schools, How Plants Grow and Behave being the Botany for Young People and Common Schools. It is intended to ground beginners in Structural Botany and the principles of vegetable life, mainly as concerns Flowering or Phanerogamous plants, with which botanical instruction should always begin; also to be a companion and interpreter to the Manuals and Floras by which the student threads his flowery way to a clear knowledge of the surrounding vegetable creation. Such a book, like a grammar, must needs abound in technical words, which thus arrayed may seem formidable; nevertheless, if rightly apprehended, this treatise should teach that the study of botany is not the learning of names and terms, but the acquisition of knowledge and ideas. No effort should be made to commit technical terms to memory. Any term used in describing a plant or explaining its structure can be looked up when it is wanted, and that should suffice. On the other hand, plans of structure, types, adaptations, and modifications, once understood, are not readily forgotten; and they give meaning and interest to the technical terms used in explaining them.

In these Elements naturally no mention has been made of certain terms and names which recent cryptogamically-minded botanists, with lack of proportion and just perspective, are endeavoring to introduce into phanerogamous botany, and which are not needed nor appropriate, even in more advanced works, for the adequate recognition of the ascertained analogies and homologies.

As this volume will be the grammar and dictionary to more than one or two Manuals, Floras, etc., the particular directions for procedure which were given in the First Lessons are now relegated to those works themselves, which in their new editions will provide the requisite explanations. On the other hand, in view of such extended use, the Glossary at the end of this book has been considerably enlarged. It will be found to include not merely the common terms of botanical description but also many which are unusual or obsolete; yet any of them may now and then be encountered. Moreover, no small number of the Latin and Greek words which form the whole or part of the commoner specific names are added to this Glossary, some in an Anglicized, others in their Latin form. This may be helpful to students with small Latin and less Greek, in catching the meaning of a botanical name or term.

The illustrations in this volume are largely increased in number. They are mostly from the hand of Isaac Sprague.

It happens that the title chosen for this book is that of the author's earliest publication, in the year 1836, of which copies are rarely seen; so that no inconvenience is likely to arise from the present use of the name.

ASA GRAY.

Cambridge, Massachusetts,

March, 1887.

CONTENTS.

Page

SECTION I. INTRODUCTORY9

SECTION II. FLAX AS A PATTERN PLANT11

Growth from the Seed, Organs of Vegetation11

Blossoming, Flower, &c. 14

SECTION III. MORPHOLOGY OF SEEDLINGS15

Germinating Maples15

Cotyledons thickened, hypogæous in germination18

Store of Food external to the Embryo20

Cotyledons as to number22

Dicotyledonous and Polycotyledonous23

Monocotyledonous24

Simple-stemmed Plants26

SECTION IV. GROWTH FROM BUDS; BRANCHING27

Buds, situation and kinds27

Vigorous vegetation from strong Buds28

Arrangement of Branches29

Non-developed, Latent, and Accessory Buds30

Enumeration of kinds of Buds31

Definite and Indefinite growth; Deliquescent and Excurrent31

SECTION V. ROOTS33

Primary and Secondary. Contrast between Stem and Root34

Fibrous and Fleshy Roots; names of kinds 34

Anomalous Roots. Epiphytic and Parasitic Plants36

Duration: Annuals, Biennials, Perennials37

SECTION VI. STEMS38

Those above Ground: kinds and modifications39

Subterranean Stems and Branches42

Rootstock42

Tuber44

Corm45

Bulb and Bulblets46

Consolidated Vegetation47

SECTION VII. LEAVES49

§ 1. Leaves as Foliage49

Parts and Venation50

Forms as to general outline52

As to apex and particular outline53

As to lobing or division56

Compound, Perfoliate, and Equitant Leaves57

With no distinction of Petiole and Blade, Phyllodia, &c. 61

§ 2. Leaves of Special Conformation and Use62

Leaves for storage62

Leaves as bud-scales63

Spines64

and for Climbing64

Pitchers64

and Fly-traps65

§ 3. Stipules66

§ 4. The Arrangement of Leaves67

Phyllotaxy67

Of Alternate Leaves69

Of Opposite and Whorled Leaves71

Vernation or Præfoliation71

SECTION VIII. FLOWERS72

§ 1. Position and Arrangement, Inflorescence73

Raceme73

Corymb, Umbel, Spike, Head74

Spadix, Catkin, or Ament75

Panicle: Determinate Inflorescence76

Cyme, Fascicle, Glomerule, Scorpioid or Helicoid Cymes77

Mixed Inflorescence78

§ 2. Parts or Organs of the Flower79

Floral Envelopes: Perianth, Calyx, Corolla79

Essential Organs: Stamen, Pistil80

Torus or Receptacle81

§ 3. Plan of the Flower81

When perfect, complete, regular, or symmetrical81

Numerical Plan and Alternation of Organs82

Flowers are altered branches83

§ 4. Modifications of the Type85

Unisexual or diclinous85

Incomplete, Irregular, and Unsymmetrical86

Flowers with Multiplication of Parts88

Flowers with Union of Parts: Coalescence88

Regular Forms89

Irregular Forms90

Papilionaceous91

Labiate92

and Ligulate Corollas93

Adnation or Consolidation94

Position of Flower or of its Parts96

§ 5. Arrangement of Parts in the Bud97

Æstivation or Præfloration, its kinds97

SECTION IX. STAMENS IN PARTICULAR98

Andrœcium98

Insertion, Relation, &c.99

Anther and Filament. Pollen101

SECTION X. PISTILS IN PARTICULAR105

§ 1. Angiospermous or Ordinary Gynœcium105

Parts of a complete Pistil105

Carpels, Simple Pistil106

Compound Pistilwith Cells and Axile Placentæ107

One-celled with Free Central Placenta108

One-celled with Parietal Placentæ108

§ 2. Gymnospermous Gynœcium109

SECTION XI. OVULES110

Their Parts, Insertion, and Kinds111

SECTION XII. MODIFICATIONS OF THE RECEPTACLE112

Torus, Stipe, Carpophore, Disk113

SECTION XIII. FERTILIZATION114

§ 1. Adaptations for Pollination of the Stigma114

Close and Cross Fertilization, Anemophilous and Entomophilous115

Dichogamy and Heterogony116

§ 2. Action of the Pollen and Formation of the Embryo117

SECTION XIV. THE FRUIT117

Nature and kinds118

Berry, Pepo, Pome119

Drupe and Akene120

Cremocarp, Caryopsis, Nut121

Follicle, Legume, Capsule122

Capsular Dehiscence, Silique and Silicle123

Pyxis, Strobile or Cone124

SECTION XV. THE SEED125

Seed-coats and their appendages125

The Kernel or Nucleus, Embryo and its parts, Albumen127

SECTION XVI. VEGETABLE LIFE AND WORK128

§ 1. Anatomical Structure and Growth129

Nature of Growth, Protoplasm129

Cells and Cell-walls. Cellular Structure or Tissue130

Strengthening Cells. Wood, Wood-cells, Vessels or Ducts132

§ 2. Cell-contents136

Sap, Chlorophyll, Starch136

Crystals, Rhaphides137

§ 3. Anatomy of Roots and Stems138

Endogenous and Exogenous Stems139

Particular structure of the latter140

Wood, Sapwood and Heart-wood. The living parts of a Tree141

§ 4. Anatomy of Leaves142

Epidermis, Stomata or Breathing pores143

§ 5. Plant Food and Assimilation144

§ 6. Plant Work and Movement149

Movements in Cells or Cyclosis149

Transference from Cell to Cell150

Movements of Organs, Twining Stems, Leaf-movements150

Movements of Tendrils, Sensitiveness152

Movements in Flowers153

Movements for capture of Insects154

Work costs, using up Material and Energy155

SECTION XVII. CRYPTOGAMOUS OR FLOWERLESS PLANTS156

Vascular Cryptogams, Pteridophytes156

Horsetails (Equisetaceæ), Ferns157

Club-Mosses (Lycopodium), &c.161

Quillworts (Isoetes), Pillworts (Marsilia)161

Azolla. Cellular Cryptogams162

Bryophytes. Mosses (Musci)163

Liverworts (Hepaticæ)164

Thallophytes165

Characeæ167

Algæ, Seaweeds, &c.168

Lichenes or Lichens171

Fungi172

SECTION XVIII. CLASSIFICATION AND NOMENCLATURE175

§ 1. Kinds and Relationship175

Species, Varieties, Individuals176

Genera, Orders, Classes, &c. 177

§ 2. Names, Terms and Characters178

Nomenclature of Genera, Species, and Varieties179

Nomenclature of Orders, Classes, &c. Terminology180

§ 3. System181

Artificial and Natural182

Synopsis of Series, Classes, &c.183

SECTION XIX. BOTANICAL WORK184

§ 1. Collection or Herborization184

§ 2. Herbarium186

§ 3. Investigation and Determination of Plants187

§ 4. Signs and Abbreviations188

Abbreviations of the Names of Botanists190

Glossary combined with Index193

ELEMENTS OF BOTANY.

Section I. INTRODUCTORY.

1. Botany is the name of the science of the vegetable kingdom in general; that is, of plants.

2. Plants may be studied as to their kinds and relationships. This study is Systematic Botany. An enumeration of the kinds of vegetables, as far as known, classified according to their various degrees of resemblance or difference, constitutes a general System of plants. A similar account of the vegetables of any particular country or district is called a Flora.

3. Plants may be studied as to their structure and parts. This is Structural Botany, or Organography. The study of the organs or parts of plants in regard to the different forms and different uses which the same kind of organ may assume,—the comparison, for instance, of a flower-leaf or a bud-scale with a common leaf,—is Vegetable Morphology, or Morphological Botany. The study of the minute structure of the parts, to learn by the microscope what they themselves are formed of, is Vegetable Anatomy, or Histology; in other words, it is Microscopical Structural Botany. The study of the actions of plants or of their parts, of the ways in which a plant lives, grows, and acts, is the province of Physiological Botany, or Vegetable Physiology.

4. This book is to teach the outlines of Structural Botany and of the simpler parts of the physiology of plants, that it may be known how plants are constructed and adapted to their surroundings, and how they live, move, propagate, and have their being in an existence no less real, although more simple, than that of the animal creation which they support. Particularly, this book is to teach the principles of the structure and relationships of plants, the nature and names of their parts and their modifications, and so to prepare for the study of Systematic Botany; in which the learner may ascertain the name and the place in the system of any or all of the ordinary plants within reach, whether wild or cultivated. And in ascertaining the name of any plant, the student, if rightly taught, will come to know all about its general or particular structure, rank, and relationship to other plants.

5. The vegetable kingdom is so vast and various, and the difference is so wide between ordinary trees, shrubs, and herbs on the one hand, and mosses, moulds, and such like on the other, that it is hardly possible to frame an intelligible account of plants as a whole without contradictions or misstatements, or endless and troublesome qualifications. If we say that plants come from seeds, bear flowers, and have roots, stems, and leaves, this is not true of the lower orders. It is best for the beginner, therefore, to treat of the higher orders of plants by themselves, without particular reference to the lower.

6. Let it be understood, accordingly, that there is a higher and a lower series of plants; namely:—

Phanerogamous Plants, which come from seed and bear flowers, essentially stamens and pistils, through the co-operation of which seed is produced. For shortness, these are commonly called Phanerogams, or Phænogams, or by the equivalent English name of Flowering Plants.[1]

Cryptogamous Plants, or Cryptogams, come from minute bodies, which answer to seeds, but are of much simpler structure, and such plants have not stamens and pistils. Therefore they are called in English Flowerless Plants. Such are Ferns, Mosses, Algæ or Seaweeds, Fungi, etc. These sorts have each to be studied separately, for each class or order has a plan of its own.

7. But Phanerogamous, or Flowering, Plants are all constructed on one plan, or type. That is, taking almost any ordinary herb, shrub, or tree for a pattern, it will exemplify the whole series: the parts of one plant answer to the parts of any other, with only certain differences in particulars. And the occupation and the delight of the scientific botanist is in tracing out this common plan, in detecting the likenesses under all the diversities, and in noting the meaning of these manifold diversities. So the attentive study of any one plant, from its growth out of the seed to the flowering and fruiting state and the production of seed like to that from which the plant grew, would not only give a correct general idea of the structure, growth, and characteristics of Flowering Plants in general, but also serve as a pattern or standard of comparison. Some plants will serve this purpose of a pattern much better than others. A proper pattern will be one that is perfect in the sense of having all the principal parts of a phanerogamous plant, and simple and regular in having these parts free from complications or disguises. The common Flax-plant may very well serve this purpose. Being an annual, it has the advantage of being easily raised and carried in a short time through its circle of existence, from seedling to fruit and seed.

FOOTNOTES:

[1] The name is sometimes Phanerogamous, sometimes Phænogamous (Phanerogams, or Phænogams), terms of the same meaning etymologically; the former of preferable form, but the latter shorter. The meaning of such terms is explained in the Glossary.

Section II. FLAX AS A PATTERN PLANT.

8. Growth from the Seed. Phanerogamous plants grow from seed, and their flowers are destined to the production of seeds. A seed has a rudimentary plant ready formed in it,—sometimes with the two most essential parts, i. e. stem and leaf, plainly discernible; sometimes with no obvious distinction of organs until germination begins. This incipient plant is called an Embryo.

9. In this section the Flax-plant is taken as a specimen, or type, and the development and history of common plants in general is illustrated by it. In flax-seed the embryo nearly fills the coats, but not quite. There is a small deposit of nourishment between the seed-coat and the embryo: this may for the present be left out of the account. This embryo consists of a pair of leaves, pressed together face to face, and attached to an extremely short stem. (Fig. 2-4.) In this rudimentary condition the real nature of the parts is not at once apparent; but when the seed grows they promptly reveal their character,—as the accompanying figures (Fig. 5-7) show.

Fig. 1. Pod of Flax. 2. Section lengthwise, showing two of the seeds; one whole, the other cut half away, bringing contained embryo into view. 3. Similar section of a flax-seed more magnified and divided flatwise; turned round, so that the stem-end (caulicle) of the embryo is below: the whole broad upper part is the inner face of one of the cotyledons; the minute nick at its base is the plumule. 4. Similar section through a seed turned edgewise, showing the thickness of the cotyledons, and the minute plumule between them, i. e. the minute bud on the upper end of the caulicle.

10. Before the nature of these parts in the seed was altogether understood, technical names were given to them, which are still in use. These initial leaves were named Cotyledons. The initial stem on which they stand was called the Radicle. That was because it gives rise to the first root; but, as it is really the beginning of the stem, and because it is the stem that produces the root and not the root that produces the stem, it is better to name it the Caulicle. Recently it has been named Hypocotyle; which signifies something below the cotyledons, without pronouncing what its nature is.

Fig. 5. Early Flax seedling; stem (caulicle), root at lower end, expanded seed-leaves (cotyledons) at the other: minute bud (plumule) between these. 6. Same later; the bud developed into second pair of leaves, with hardly any stem-part below them; then into a third pair of leaves, raised on a short joint of stem; and a fifth leaf also showing. 7. Same still older, with more leaves developed, but these singly (one after another), and with joints of stem between them.

11. On committing these seeds to moist and warm soil they soon sprout, i. e. germinate. The very short stem-part of the embryo is the first to grow. It lengthens, protrudes its root-end; this turns downward, if not already pointing in that direction, and while it is lengthening a root forms at its point and grows downward into the ground. This root continues to grow on from its lower end, and thus insinuates itself and penetrates into the soil. The stem meanwhile is adding to its length throughout; it erects itself, and, seeking the light, brings the seed up out of the ground. The materials for this growth have been supplied by the cotyledons or seed-leaves, still in the seed: it was the store of nourishing material they held which gave them their thickish shape, so unlike that of ordinary leaves. Now, relieved of a part of this store of food, which has formed the growth by which they have been raised into the air and light, they appropriate the remainder to their own growth. In enlarging they open and throw off the seed-husk; they expand, diverge into a horizontal position, turn green, and thus become a pair of evident leaves, the first foliage of a tiny plant. This seedling, although diminutive and most simple, possesses and puts into use, all the Organs of Vegetation, namely, root, stem, and leaves, each in its proper element,—the root in the soil, the stem rising out of it, the leaves in the light and open air. It now draws in moisture and some food-materials from the soil by its root, conveys this through the stem into the leaves, where these materials, along with other crude food which these imbibe from the air, are assimilated into vegetable matter, i. e. into the material for further growth.

12. Further Growth soon proceeds to the formation of new parts,—downward in the production of more root, or of branches of the main root, upward in the development of more stem and leaves. That from which a stem with its leaves is continued, or a new stem (i. e. branch) originated, is a Bud. The most conspicuous and familiar buds are those of most shrubs and trees, bearing buds formed in summer or autumn, to grow the following spring. But every such point for new growth may equally bear the name. When there is such a bud between the cotyledons in the seed or seedling it is called the Plumule. This is conspicuous enough in a bean (Fig. 29.), where the young leaf of the new growth looks like a little plume, whence the name, plumule. In flax-seed this is very minute indeed, but is discernible with a magnifier, and in the seedling it shows itself distinctly (Fig. 5, 6, 7).

13. As it grows it shapes itself into a second pair of leaves, which of course rests on a second joint of stem, although in this instance that remains too short to be well seen. Upon its summit appears the third pair of leaves, soon to be raised upon its proper joint of stem; the next leaf is single, and is carried up still further upon its supporting joint of stem; and so on. The root, meanwhile, continues to grow underground, not joint after joint, but continuously, from its lower end; and commonly it before long multiplies itself by branches, which lengthen by the same continuous growth. But stems are built up by a succession of leaf-bearing growths, such as are strongly marked in a reed or corn-stalk, and less so in such an herb as Flax. The word joint is ambiguous: it may mean either the portion between successive leaves, or their junction, where the leaves are attached. For precision, therefore, the place where the leaf or leaves are borne is called a Node, and the naked interval between two nodes, an Internode.

Fig. 8. Upper part of Flax-plant in blossom.

14. In this way a simple stem with its garniture of leaves is developed from the seed. But besides this direct continuation, buds may form and develop into lateral stems, that is, into branches, from any node. The proper origin of branches is from the Axil of a leaf, i. e. the angle between leaf and stem on the upper side; and branches may again branch, so building up the herb, shrub, or tree. But sooner or later, and without long delay in an annual like Flax, instead of this continuance of mere vegetation, reproduction is prepared for by

15. Blossoming. In Flax the flowers make their appearance at the end of the stem and branches. The growth, which otherwise might continue them farther or indefinitely, now takes the form of blossom, and is subservient to the production of seed.

Fig. 9. Flax-flowers about natural size. 10. Section of a flower moderately enlarged, showing a part of the petals and stamens, all five styles, and a section of ovary with two ovules or rudimentary seeds.

16. The Flower of Flax consists, first, of five small green leaves, crowded into a circle: this is the Calyx, or flower-cup. When its separate leaves are referred to they are called Sepals, a name which distinguishes them from foliage-leaves on the one hand, and from petals on the other. Then come five delicate and colored leaves (in the Flax, blue), which form the Corolla, and its leaves are Petals; then a circle of organs, in which all likeness to leaves is lost, consisting of slender stalks with a knob at summit, the Stamens; and lastly, in the centre, the rounded body, which becomes a pod, surmounted by five slender or stalk-like bodies. This, all together, is the Pistil. The lower part of it, which is to contain the seeds, is the Ovary; the slender organs surmounting this are Styles; the knob borne on the apex of each style is a Stigma. Going back to the stamens, these are of two parts, viz. the stalk, called Filament, and the body it bears, the Anther. Anthers are filled with Pollen, a powdery substance made up of minute grains.

17. The pollen shed from the anthers when they open falls upon or is conveyed to the stigmas; then the pollen-grains set up a kind of growth (to be discerned only by aid of a good microscope), which penetrates the style: this growth takes the form of a thread more delicate than the finest spider's web, and reaches the bodies which are to become seeds (Ovules they are called until this change occurs); these, touched by this influence, are incited to a new growth within, which becomes an embryo. So, as the ovary ripens into the seed-pod or capsule (Fig. 1, etc.) containing seeds, each seed enclosing a rudimentary new plantlet, the round of this vegetable existence is completed.

Section III. MORPHOLOGY OF SEEDLINGS.

18. Having obtained a general idea of the growth and parts of a phanerogamous plant from the common Flax of the field, the seeds and seedlings of other familiar plants may be taken up, and their variations from the assumed pattern examined.

19. Germinating Maples are excellent to begin with, the parts being so much larger than in Flax that a common magnifying glass, although convenient, is hardly necessary. The only disadvantage is that fresh seeds are not readily to be had at all seasons.

Fig. 11. Embryo of Sugar Maple, cut through lengthwise and taken out of the seed. 12, 13. Whole embryo of same just beginning to grow; a, the stemlet or caulicle, which in 13 has considerably lengthened.

20. The seeds of Sugar Maple ripen at the end of summer, and germinate in early spring. The embryo fills the whole seed, in which it is nicely packed; and the nature of the parts is obvious even before growth begins. There is a stemlet (caulicle) and a pair of long and narrow seed-leaves (cotyledons), doubled up and coiled, green even in the seed, and in germination at once unfolding into the first pair of foliage-leaves, though of shape quite unlike those that follow.

21. Red Maple seeds are ripe and ready to germinate at the beginning of summer, and are therefore more convenient for study. The cotyledons are crumpled in the seed, and not easy to straighten out until they unfold themselves in germination. The story of their development into the seedling is told by the accompanying Fig. 14-20; and that of Sugar Maple is closely similar. No plumule or bud appears in the embryo of these two Maples until the seed-leaves have nearly attained their full growth and are acting as foliage-leaves, and until a root is formed below. There is no great store of nourishment in these thin cotyledons; so further growth has to wait until the root and seed-leaves have collected and elaborated sufficient material for the formation of the second internode and its pair of leaves, which lending their help the third pair is more promptly produced, and so on.

22. Some change in the plan comes with the Silver or Soft White Maple. (Fig. 21-25). This blossoms in earliest spring, and it drops its large and ripened keys only a few weeks later. Its cotyledons have not at all the appearance of leaves; they are short and broad, and (as there is no room to be saved by folding) they are straight, except a small fold at the top,—a vestige of the habit of Maples in general. Their unusual thickness is due to the large store of nutritive matter they contain, and this prevents their developing into actual leaves. Correspondingly, their caulicle does not lengthen to elevate them above the surface of the soil; the growth below the cotyledons is nearly all of root. It is the little plumule or bud between them which makes the upward growth, and which, being well fed by the cotyledons, rapidly develops the next pair of leaves and raises them upon a long internode, and so on. The cotyledons all the while remain below, in the husk of the fruit and seed, and perish when they have yielded up the store of food which they contained.

Fig. 14. One of the pair of keys or winged fruits of Red Maple; the seed-bearing portion cut open to show the seed. 15.