76 FOUNDATIONS OF BOTANY 
found in some mints and in many grasses and sedges, the 
real nature of the creeping underground stem is shown by 
sp itigoltg the presence upon its sur- 
iM 
face of many scales, which 
are reduced leaves. Root- 
stocks of this sort often 
extend horizontally for 
long distances in the case 
of grasses like the sea rye 
grass (Plate I), which roots 
itself firmly and thrives in 
shifting sand-dunes. In 
the stouter rootstocks, like 
that of the iris (Fig. 44) 
and the Caladium (Fig. 
45), this stem-like charac- 
ter is less evident. The 
potato is an excellent ex- 
ample of the short and 
much-thickened under- 
ground stem known as a 
tuber. 
It may be seen from Fig. 
46 that the potatoes are 
none of them borne on true 
roots, but only on subter- 
ranean 
= LE —— 
—=S——=—._—sébranches, 
whichare 
Fic. 43.— Rootstock of Cotton-Grass (Eriophorum). stouter 
and more cylindrical than most of the roots. The “eyes” 
