OUTLINES OF BOTANY. XV 
of an annual or perennial, or the lowest branches of a piant, 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 Stoek 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 
ma bud at the top. A potato is an annual tuberous rootstock with several 
uds. 
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- 
eealed, 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 in 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; 
