Page:Flora Hongkongensis.djvu/32

vi 18. Roots ordinarily produce neither buds, leaves, nor flowers. Their branches, called fibres when slender and long, proceed irregularly from any part of their surface.

19. Although roots proceed usually from the base of the stem or stock, they may also be produced from the base of any bud, especially if the bud lie along the ground, or is otherwise placed by nature or art in circumstances favourable for their development, or indeed occasionally from almost any part of the plant. They are then often distinguished as adventitious, but this term is by some appHed to all roots which are not in prolongation of the original radicle.

20. Roots are

fibrous, when they consist chiefly of slender fibres.

tuberous, when either the main root or its branches are thickened into one or more short fleshy or woody masses called tubers (25).

taproots, when the main root descends perpendicularly into the earth, emitting only very small fibrous branches.

22. The stock of a herbaceous perennial, or the lower part of the stem of an annual or perennial, or the lowest branches of a plant, are sometimes undergroimd and assume the appearance of a root. They then take the name of rhizome. The rhizome may always be distinguished from the true root by the presence or production of one or more buds, or leaves, or scales.

22. The Stock of a herbaceous perennial, in its most complete state, includes a small portion of the summits of the previous year's roots, as well as of the base of the previous year's stems. Such stocks will increase yearly, so as at length to form dense tufts. They will often preserve through the winter a few leaves, amongst which are placed the buds which grow out into stems the following year, wliilst the under side of the stock emits new roots from or amongst the remains of the old ones. These perennial stocks only difier from the permanent base of an undershrub in the shortness of the perennial part of the stems and in their textm'e usually less woody.

23. In some perennials, however, the stock consists merely of a branch, which proceeds in autumn from the base of the stem either aboveground or underground, and produces one or more buds. This branch, or a portion of it, alone survives the winter. In the following year its buds produce the new stem and roots, whilst the rest of the plant, even the branch on which these buds were formed, has died away. These annual stocks, called sometimes hybemacula, offsets, or stolons, keep up the commvmication between the annual stem and root of one year and those of the following year, thus forming altogether a perennial plant.

24. The stock, whether annual or perennial, is often entirely undergroimd or root-like. This is the rootstock, to which some botanists limit the meaning of the term rhizome. When the stock is entfrely root-hke, it is popvdai-ly called the crown of the root.

25. The term tuber is applied to a short, thick, more or less succulent rootstock or rhizome, as well as to a root of that shape (20), although some botanists propose to restrict its meaning to the one or to the other. An Orchis tuber, called by some a knob, is an annual tuberous rootstock with one bud at the top. A potato is an aimual tuberous rootstock with several buds.

26. A bulb is a stock of a shape approaching to globular, usually rather conical above and flattened underneath, in which the bud or buds are concealed, or nearly so, under scales. These scales are the more or less thickened bases of the decayed leaves of the preceding year, or of the undeveloped leaves of the future year, or of both. Bulbs are annual or perennial, usually imderground or close to the ground, but occasionally buds in the axils of the upper leaves become transformed into bulbs. Bulbs are said to be scaly when their scales are thick and loosely imbricated, tunicated when the scales are thinner, broader, and closely rolled round each other in concentric layers.

27. A corm is a tuberous rootstock, usually annual, shaped like a bulb, but in which the bud or buds are not covered by scales, or of which the scales are very thin and membranous.