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 



the presence upon its sur- 

 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 

 branches, 

 which are 



FlG. 43. Kootstock of Cotton-Grass (Eriophorum). S to U t 6 f 



and more cylindrical than most of the roots. The " eyes " 



