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 sui"- 

 face of many scales, -vrhich 

 are reduced le^ives. 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 

 rshifting 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 

 tvher. 



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 



Fig. 43. — Bootatock of Cotton-Grass (Erioplwrani). a tri n t a r 



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



