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 
Fic. 158.— A corm of Gladiolus, showing by scar-like rings left by 
young corms developing at the base of the the decay of former leaves. 
eons 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 
