Botany

That branch of science which treats of plants. On account of its wide scope and great complexity, it has been separated into subdivisions. Structural Botany treats of the gro anatomy of plants; Plant Histology of their minute anatomy; Plant Morphology, of the forms of plants and their organs; Plant Physiology, of the functions of these organs; Systematic Botany, of the relationship and cla ification of plants; Geographical Botany, of the distribution of plants over the surface of the globe; Paleobotany, of the vegetable life of past ages and the succe ive appearance in the world of the great cla es of plants, as traced in their fo il remains; and Economic Botany, which deals with the products of plants and their uses. The field is so vast and the science has been so developed, through the labors of many eminent men, especially since the days of Linnæus (1707-1778), and is now being pushed so rapidly forward, that an intimate knowledge of the whole is removed beyond the powers of individuals. Yet any one of the branches of the science can be philosophically studied only in the light of all the others, making e ential to the pursuit of any one a general knowledge of the whole. The e ential functions of plants are: first, the purification of the air by the withdrawal from it of carbonic acid gas, the retention of the carbon, and the restoration of free oxygen, thus rendering the atmosphere fit for the support of animal life; and, second, the production of food for the use of animals, chiefly in the forms of herbage, foliage, fruits, and seeds. Plants are the great organizers of inorganic matter, and, as this function is entirely absent in animals, the animal world could not maintain an independent existence. The vegetable series presents an almost infinite variety of forms, from the lowly organized unicellular bacterium and green-slime, or still lower slime-mould, to the infinitely complex and majestic oak of the forest, yet so delicate is the structure, so accurate the adaptation to habits and surroundings in all, that one is scarcely more wonderful than another. wall of cellulose containing during the active period, that which is the e ential living portion, the protoplasm, a semifluid, transparent substance, endued with the power of motion, of absorbing fluids, secreting cellulose, and performing all the a imilative and metastatic functions of plant life under proper conditions. It also po e es the power of self-division through a denser portion called the nucleus of the cell, by which means the number of cells is increased, and, in the higher plants, the body of the plant is built up and formed and its various organs developed and matured. As the cell increases in age, especially in woody plants, the protoplasm gradually disappears, the wall thickens, and the cell becomes variously modified in form and function, remaining as an inactive and e entially dead portion of the plant body. Plants are primarily cla ified as to their mode of reproduction, whether by spore or seed, into: I. The Thallophyta , with comparatively little differentiation of ti ue and organs, consisting of the (a) Algæ , chlorophyll-bearing plants, inhabiting salt or fresh water, comprising the Sea-weeds, Pond-scums, and Diatoms; and (b) the Fungi , aërial or subterraneous plants occasionally growing within other plants or in animals, without chlorophyll, and living parasitically or saprophytically, i.e. , on living or dead organic matter, comprising the Mushrooms, Blights, Moulds, etc. II. The Bryophyta , the Liver-worts and Mo es. III. The Pteridophyta , the Ferns, Club-mo es and their allies. IV. The Spermophyta , divided into the Gymnos per me , with the ovary open, and the Angiospermæ , with closed ovary, embracing the Monocotyledonæ and Dicotyledone ; Monocotyledons have an embryo embryo with a single cotyledon, stem mostly simple and endogenous, i . e., with the woody bundles growing without regular arrangement throughout the stem, bark and wood not distinguished, leaves parallel-veined, floral parts chiefly in threes. In Dicotyledons the embryo has two cotyledons, the stem is mostly branched and exogenous, with the woody bundles of each period of growth in concentric layers from within outward, bark separable from the wood, leaves netted-veined, floral parts chiefly in fours or fives. Reproduction among the flowerle plants is accomplished in many cases by both sexual and asexual spores, the manner of their formation being various in the different orders and intricate in detail. The asexual spores germinate quickly, and rapidly increase the number of individuals, while the sexual undergo a period of rest and germinate when the conditions become favorable. In many an alternation of generations takes place, notably in the Pteridophyta the well-known leafy form of which bears asexual spores only in the sori or fruit-dots. These upon germination develop into a minute thalloid plant, the prothallium, which bears the sexual organs, and the matured sexual spore, germinating, produces the asexual plant. The flowering plants, as has been said, reproduce regularly by seeds, though there are many examples of self-division, as in the rooting of stems, the budding of roots, and the dying off of the older portions of branching rhizomes, leaving the branches separate. The e ential portion of the seed is the embryo, having in Dicotyledons a caulicle and two cotyledons, which, with their point of junction, form the node, internode and leaves of the first phyton or element of which the plant body is composed. There is also between the cotyledons, at the apex of the caulicle, the plumule or bud from which the second phyton develops. The embryo may or may not be furnished with a supply of nutriment, stored either in the cotyledons or externally in the so-called albumen of the seed, and the whole is surrounded by a double protecting cover, the seed-coats. Under proper conditions of heat and moisture the seed germinates, sending out from the tip of the caulicle the primary root, which turns downward into the soil, under the influence of geotropism, while the stem pushes upward to the light under the influence of the opposite force or negative geotropism. From this time there is a gradual and often rapid development of the ti ues and organs of the plant till the point of flowering is reached and the plant produces seeds in all e entials like the one from which it sprang, thus completing the cycle of life. The organs of the plant are all morphologically referable to three forms, the root, stem and leaf, but of these there are almost innumerable modifications for adaptation to various functions and conditions. The root is most constant, and is usually an irregularly branched fibrous organ, at its growing tips actively absorbing the nutritious fluids of the soil, but it is sometimes thickened by a deposition of reserve material, as in the beet and carrot. Stems, and branches, which are secondary stems, are either subterranean or aerial, and may be modified in the former case, as thickened rootstocks, bulbs, corms and tubers; in the latter, as thorns, spines, tendrils, floral axes or receptacles, runners, ennial or perennial; as to their character, herbaceous or woody; and as to their position, erect, inclined, decumbent, trailing or climbing. Stems bear at their nodes the third form of organ, the leaf, in arrangement either opposite, alternate, or whorled. The axis or angle between the leaf and stem is the point of production of the bud, which is morphologically an undeveloped leafy stem, and is formed in summer to develop the following season. In its ordinary character, as foliage, the leaf consists of three parts, any of which may be wanting; viz., the petiole or leafstalk, the lamina or blade, and a pair of leafy appendages at the base of the petiole, known as stipules. The most imporant part of the leaf, and therefore least frequently absent, is the blade, which consists of a framework of woody bundles, supporting the soft ti ue, the cells of which are loosely arranged and abundantly supplied with chlorophyll, the green coloring matter of the leaf, which, in the presence of sunlight enables the protoplasm of the cells to break up the gaseous and fluid substances absorbed by the leaves and root, and to recombine their elements as starch, the primary a imilative food product of the plant. The intercellular spaces of the leaf communicate freely with the air by means of the stomata or breathing pores, which have the power of opening and closing according to external conditions and are usually most abundant on the lower surface of the leaf and often wholly wanting above. This enables the leaf readily to absorb the useful gaseous elements and to throw off the unused oxygen. The The leaf is variously modified as bulb, bud, and involucral scales, scales of rhizomes and tubers, spines, tendrils, bracts, etc., but especially in the flower, the reproductive organ of the plant, in which the sepals, petals, stamens and the carpels of the pistil are modified leaves. Of these the stamens and pistils only are e ential organs and may be together in the same flowers (perfect), or in different flowers on the same plant (monœcio us), or on different plants (diœcio us). The stamen consists of the filament and anther, in the latter of which are produced pollen grains, the male reproductive spores. parts of the pistil are the ovary, style and stigma. Within the ovary, upon the placente, which are formed by the margins of the modified carpellary leaves and may vary in number and position with the number of carpels and their mode of compounding, are borne the ovules, minute sac-like bodies with an open pore or foramen and containing the germinal vesicle or female reproductive body. Fertilization takes place by the falling of the pollen upon the moist surface of the stigma, where it germinates and sends down a tube through the loose ti ue of the style and the foramen of the ovule to the germinal vesicle, where it unites its protoplasm with that of the latter. Immediately a new growth begins which ends in the development of the ovule into a seed. The floral envelopes, the calyx and corolla, are protective, or, by their bright colors and a ociated nectar glands, attractive to insects, upon whose visitation many plants are entirely dependent for fertilization (entomophilous). Either or both may be wanting, as in plants dependent for fertilization upon the winds (anemophilous). Flowers may be solitary or variously grouped in clusters; e.g. , the raceme, cyme, corymb, umbel, spike, catkin, head, fascicle, glomerule and panicle. At the maturity of the seed occurs also the ripening of the fruit in which the seeds are inclosed. It may consist of the ovary only or may include, as in many fleshy fruits, the calyx, receptacle, and even bracts.