5 



GROWTH AND WORK OF PLANTS 



Fig. 48- 

 Easter lily "bulbs." 



flattened circular or oval body. The outer leaves are usually 

 dead, thin, papery and brown. A longitudinal section through 

 the middle shows well the thickness and relation of the leaves. 

 At the lower end can be seen the flattened very short stem to the 



upper surface of which the 

 leaves are attached, while the 

 roots extend from the lower 

 side (fig. 47). The food is 

 stored in the fleshy leaves. 

 It is of a protein or nitro- 

 genous nature, i.e., it con- 

 tains nitrogen in addition to 

 carbon, hydrogen, and oxy- 

 gen. The presence of pro- 

 teins can be shown by heating 

 portions of an onion in nitric acid. The liquid becomes pale 

 yellow in color. Adding a small quantity of ammonium 

 hydrate the color becomes orange. The lily bulb (caster lily, 

 fig. 48) is similar to that of the onion but the thickened leaves 

 are not so closely and compactly crowded. 



80. The corm. This is a short, thick, fleshy shoot in which 

 food is stored. The Indian turnip, or Jack-in-the-pulpit, is a 

 good exam'ple. This is circular and somewhat flattened or oval. 

 It is perennial, increasing gradually in size usually each year on 

 the upper side, while the lower side gradually dies off. Prop- 

 agation of the corm usuaHy takes place by the formation of small 

 corms on the side. T? hese eventually separate and form new 

 plants. New corms are also formed by the germination of the 

 seed. 



81. Tubers. A tuber is a fleshy thickened portion of a 

 subterranean stem containing large quantities of plant food. 

 There are rudimentary scale leaves, in the axils of which are 

 buds. These buds often resemble an eye, as in the potato tuber, 

 when they are called "eyes." The potato plant has slender 

 underground stems as well as aerial stems. It is on the ends of 

 these underground stems, which are thicker than the roots, that 



