UNDERGROUND STEMS 



53 



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. 

 FIG. 48. Bulb of hyacinth Jt 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). na ! se f i( f of an 



onion leaf 

 The variously modified forms of under- 



. sea, thickened base of 



ground stems just discussed illustrate in a i ea f , forming a bulb 

 marked way the storage of nourishment during scale ; s > thin sheath 



J fe of leaf; bl, blade of 



the winter, or the rainless season, as the case the leaf -int, hollow 

 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 



sea 



