UNDERGROUND STEMS 



53 



FIG. 48. Bulb of hyacinth 



Exterior view, and split lengthwise. 

 After Faguet 



Rootstocks of this sort often extend horizontally for long dis- 



tances 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. 45) and 

 the caladium (Fig. 46), this 

 stem-like character is less evi- 

 dent. The potato is an excel- 

 lent example of the short and 

 much-thickened underground 

 stem known 

 as a tuber. 



It may be 

 seen from 

 Fig. 47 that 



the potatoes are none of them borne on true 



roots, but only on subterranean branches, 



which are stouter and more cylindrical than 



most of the roots. The " eyes " of the potato 



are rudimentary leaves and buds. 



Bulbs, whether coated like those of the 



onion or the hyacinth (Fig. 48), or scaly like 



those of the lily, are merely very short and 



stout underground stems, covered with closely 



crowded scales or layers which represent FIG. 49. Longitudi- 



leaves or the bases of leaves (Fig. 49). 



The variously modified forms of under- 



. . sea, thickened base of 



ground stems just discussed illustrate in a leaf , forming a bulb 



scale '> s > tnin sheath 

 of leaf; bl, blade of 



the leaf ;int, hollow 



sea 



nal section of an 

 onion leaf 



marked way the storage of nourishment during 



J 



the winter, or the rainless season, as the case 



may be, to provide the material for rapid 



growth during the active season. It is inter- 



esting to notice that a majority of the early flowering herbs 



in temperate climates, like the crocus, the snowdrop, the spring 



