CHAP. II. 
STEM. 
63 
such plants when they are not caulescent. It is composed of 
cellular tissue, traversed by bundles of vessels and woody 
fibre, and has the form of a flattened disk. The fleshy root 
of the Arum, that of the Crocus and the Colchicum, are all 
different forms of the Cormus. It has been called hulho-tuber 
by Ker, and hulhus solidus by many others ; the last is a con- 
tradiction in terms. {See Bulb.) 
The stems of Palms have by some writers been considered 
as an extended cormus, and not a true stem, but this seems an 
extravagant application of the term ; or rather an application 
which reduces the signification of the term to nothing. A 
cormus is a depressed subterranean stem of a particular kind ; 
the trunk of a Palm is, as far as its external character is con- 
cerned, as much a stem as that of an Oak. De Candolle ap- 
plies the name cormus only to the stems of Gryptogamous 
plants, and refers to it the Anabices of Necker. 
The Tuber, fig. 24. (Tuberculum if very small), is an 
annual thickened subterranean stem, provided at the sides 
with latent buds, from which new plants are produced the 
succeeding year, as in the Potato and Arrow-root. A tuber 
is, in reality, a part of a subterranean stem, excessively en- 
larged by the developement to an unusual degree of cellular 
tissue. The usual consequences attendant upon such a state 
take place ; the regular and symmetrical arrangement of the 
buds is disturbed ; the buds themselves are sunk beneath the 
surface, or half obliterated, and the whole becomes a shapeless 
mass. Such is not, however, always the case; the enlarge- 
ment sometimes occurs without being accompanied by much 
distortion, and the true nature of the tuber stands revealed ; 
this is remarkably the case in the Asparagus Potato. In most, 
perhaps all tubers, a great quantity of amylaceous matter 
is deposited, on which account they are frequently found to 
possess highly nutritive properties. 
The Creeping stem, fig. 25. (soboles),\% a slender stem, which 
creeps along horizontally below the surface of the earth, emit- 
ting roots and new plants at intervals, as in the Triticum 
repens. It differs in nothing whatever from the rhizoma, ex- 
cept in being subterranean. This is what many botanists call 
