182 



STEMS 



cinth, and Tulip. The edible portion of the Onion bulb consists 

 mainly of the fleshy scale-like leaves, in which the food has been 

 stored. (Fig. 157.) 



Not all bulbs, however, are produced underground, for small 



Onion bulbs, called bulb- 

 lets, often replace flower 

 buds in the common 

 Onion. These small bulbs 

 are sometimes known as 

 "Onion sets." Some Lilies 

 also produce small bulbs 

 in the leaf axils. Such 

 bulbs, although they re- 

 semble underground bulbs 

 in structure, are not 

 formed in connection with 

 underground stems. 



Corms are very short, 

 solid, vertical, under- 

 ground stems, usually 

 bearing roots on their 

 lower and leaves and buds 

 on their upper surface. 

 However, buds may arise 

 anywhere and roots are 

 sometimes present at the 

 upper end of the corm, as 

 in the Jack-in-the-pulpit. 

 Corms are usually marked 

 by scar-like rings left by 

 the decay of former leaves. 

 From the buds of the old 

 corm new corms develop. (Fig. 158.) The most familiar corms 

 are those of the Indian Turnip, Crocus, Timothy, Cyclamen, and 

 Gladiolus. 



General Structure of Stems 



Stems have a cylindrical shape, which is associated with the 

 circular arrangement of their strengthening tissue. By being 

 arranged in a circle and near the periphery of the stem, the 



FIG. 158. A corm of Gladiolus, showing 

 young corms developing at the base of the 

 old one. 



