120 CREEPING STEM.—TUBER. 
more slender form, its commonly greater length, and its 
entirely subterranean course. The Sand Sedge (Carex arenaria) 
( fig. 235), and the Couch Grass (Triticwm repens), afford 
good examples of this stem. In some instances such stems 
serve important purposes in nature ; thus those of the Sand 
Sedge or Carex, by spreading through the sand of the sea- 
shore, and in this way binding it together, prevent it from being 
washed away by the receding waves. Others, like those of the 
Couch Grass, are the pest of the agriculturist, who finds it very 
difficult to destroy such stems by cutting them into pieces, for 
as every node is capable of developing a leaf-bud and roots, 
each of the pieces into which they will then be divided may 
become an independent individual ; and therefore such a 
Bree 23h. 
Fig. 235. Creeping stem of the Sand Carex (Carer arenaria). 1. Terminal 
bud by which the stem continues to elongate, 2, 3, 4. Shoots produced 
from former buds. 
process, instead of destroying such plants, only serves the 
purpose of still further multiplying them by placing the 
separated parts under more tavourable circumstances for 
development. 
b. The Tuber (figs. 236 and 237).—This is a subterranean 
stem or branch, arrested in its growth, and excessively enlarged 
by the deposition of starch or other nutritious substance in its 
tissue. It has upon its surface a variable number of little 
buds, or eyes as they are sometimes called, from which new 
plants are ultimately formed. The presence of these’ buds 
indicates its nature asa kind of stem. This stem-like nature 
of the tuber is also clearly proved by the practice commonly 
adopted for propagating potatoes, the tuber being cut into 
pieces, each piece containing one or more buds. When these 
pieces are placed under favourable circumstances for develop- 
ment, the buds are at first nourished by the matter which 
surrounds them, and are thus enabled to put forth roots and 
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