botanical species may be an annual or a perennial, a herbaceous perennial or an undershrub, an undershrub or a shrub, a shrub or a tree, according to climate, treatment, or variety.
14. Plants are usually terrestrial, that is, growing on earth, or aquatic, i. e. growing in water; but sometimes they may be found attached by their roots to other plants, in which case they are epiphytes when simply growing upon other plants without penetrating into their tissue, parasites when their roots penetrate into and derive more or less nutriment from the plant to which they are attached.
15. The simplest form of the perfect plant, the annual, consists of—
(1) The Root, or descending axis, which grows downwards from the stem, divides and spreads in the earth or water, and absorbs food for the plant through the extremities of its branches.
(2) The Stem, or ascending axis, which grows upwards from the root, branches and bears first one or more leaves in succession, then one or more flowers, and finally one or more fruits. It contains the tissues or other channels (217) by which the nutriment absorbed by the roots is conveyed in the form, of sap (192) to the leaves or other points of the surface of the plant, to be elaborated or digested (218), and afterwards redistributed over different parts of the plant for its support and growth.
(3) The Leaves, usually flat, green, and horizontal, are variously arranged on the stem and its branches. They elaborate or digest (218) the nutriment brought to them through the stem, absorb carbonic acid gas from the air, exhaling the superfluous oxygen, and returning the assimilated sap to the stem.
(4) The Flowers, usually placed at or towards the extremities of the branches. They are destined to form the future seed. When perfect and complete they consist: 1st, of a pistil in the centre, consisting of one or more carpels, each containing the germ of one or more seeds; 2nd, of one or more stamens outside the pistil, whose action is necessary to fertilize the pistil or enable it to ripen its seed; 3rd, of a perianth or floral envelope, which usually encloses the stamens and pistil when young, and expands and exposes them to view when fully formed. This complete perianth is double; the outer one, called Calyx, is usually more green and leaf-like; the inner one, called the Corolla, more conspicuous, and variously coloured. It is the perianth, and especially the corolla, as the most showy part, that is generally called the flower in popular language.
(5) The Fruit, consisting of the pistil or its lower portion, which persists or remains attached to the plant after the remainder of the flower has withered and fallen off. It enlarges and alters more or less in shape or consistence, becomes a seed-vessel, enclosing the seed until it is ripe, when it either opens to discharge the seed or falls to the ground with the seed. In popular language the term fruit is often limited to such seed-vessels as are or look juicy and eatable. Botanists give that name to all seed-vessels.
16. The herbaceous perennial resembles the annual during the first year of its growth; but it also forms (usually towards the close of the season), on its stock (the portion of the stem and root which does not die), one or more buds, either exposed, and then popularly called eyes, or concealed among leaves. These buds, called leaf-buds, to distinguish them from flower-buds or unopened flowers, are future branches as yet undeveloped; they remain dormant through the winter, and the following spring grow out into new stems bearing leaves and flowers like those of the preceding year, whilst the lower part of the stock emits fresh roots to replace those which had perished at the same time as the stems.
17. Shrubs and trees form similar leaf-buds either at the extremity of their branches, or along the branches of the year. In the latter case these buds are usually axillary, that is, they appear in the axil of each leaf, i. e. in the angle formed by the leaf and the branch. When they appear at any other part of the plant they are called adventitious. If these buds by producing roots (19) become distinct plants before separating from the parent, or if adventitious leaf-buds are produced in the place of flowers or seeds, the plant is said to be viviparous or proliferous.
