OUTLINES OF BOTANY. XV 



of an annual or perennial, or the lowest branches of a plant, are sometimes 

 underground 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. 



§ 3. The Stock. 



22. The Stock of an 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, whilst the under side of the stock 

 emits new roots from or amongst the remains of the old ones. These peren- 

 nial stocks only differ from the permanent base of an undershrub in the 

 shortness of the perennial part of the stems and in their texture 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 some- 

 times hybernacula, offsets, or stolons, keep up the communication 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 underground 

 or root-like. This is the rootstock, to which some botanists limit the mean- 

 ing of the term rhizome. When the stock is entirely root-like, it is popu- 

 larly 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 annual 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 con- 

 cealed, or nearly so, under scales. These scales are the more or less thick- 

 ened 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, usu- 

 ally underground 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 con- 

 centric layers. 



27. A corm is a tuberous rootstock, usually annual, shaped like a bulb, 

 but ia. which the bud or buds are not covered by scales, or of which the 

 scales are very thin and membranous. 



§ 4. The Stem. 



28. Stems are 



erect, when they ascend perpendicularly from the root or stock ; 



