82 
ORGANOGRAPHY. 
BOOK I. 
The Tuber, Jig. 2Q. (Tuherculum 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 pos- 
sess highly nutritive properties. 
The Creeping stem, Jig. 27. {soholes), is 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 
a creeping root. It is one of those provisions of nature by 
which the barren sands that bound the sea are confined 
within their limits ; most of the plants which cover such soils 
being provided with subterranean stems of this kind. It is 
also extremely tenacious of life, the buds at every node being 
capable of renewing the existence of the individual ; hence 
the almost indestructible properties of the Couch grass, Triti- 
cum repens, by the ordinary operations of husbandry : divi- 
sions of its creeping stem, by cutting and tearing, producing 
no other effect than that of calling new individuals into exist- 
ence as fast as others are destroyed. The term soboles is 
applied by Link and De Candolle to the sucker of trees and 
shrubs. (See Surculus.) 
Of the AERIAL stem, the most remarkable forms are the 
following : — 
