The Elements of Botany.

by Asa Gray.

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 ill.u.s.trate 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 a.n.a.logies and h.o.m.ologies.

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 ill.u.s.trations in this volume are largely increased in number. They are mostly from the hand of Isaac Sprague.

It happens that the t.i.tle 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, Ma.s.sachusetts, _March, 1887_.

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, cla.s.sified according to their various degrees of resemblance or difference, const.i.tutes 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 a.s.sume,--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 _Phaenogams_, 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, Algae or Seaweeds, Fungi, etc. These sorts have each to be studied separately, for each cla.s.s 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 princ.i.p.al 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 _Phaenogamous_ (_Phanerogams_, or _Phaenogams_), 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 ill.u.s.trated 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.

[Ill.u.s.tration: 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 p.r.o.nouncing what its nature is.

[Ill.u.s.tration: 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 a.s.similated 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.

[Ill.u.s.tration: 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.

[Ill.u.s.tration: 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 k.n.o.b 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 k.n.o.b 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.