GERMINATION IN PARTICULAR SEEDS 



175 



its central part "comes up" first, (a, Fig. 312.) Presently 

 it draws the cotyledons out of the seed-coats, and then it 

 straightens and the cotyledons expand. These coty- 

 ledons, or "halves of the bean," persist for some 

 time. (b, Fig. 312.) They often become green and 

 probably perform some function of 

 foliage. Because of its large size, Lim? 

 bean shows all these parts well. 



342. Germination of Castor Bean. 

 In the castor bean the hilum and 

 micropyle are at the smaller end. (Fig. 

 313.) The bean "comes up" with a 

 loop, which indicates that the hypocotyl 

 greatly elongates. On exam- 

 ining a germinating seed, however, it will be 

 found that the cotyledons are contained inside a 

 fleshy body or sac. (a, Fig. 314.) This 

 sac is the endosperm. To its inner sur- 

 face the thin, veiny cotyledons are 

 very closely appressed, absorbing its 

 substance. (Fig. 315.) The cotyledons 

 increase in size as they reach the air (Fig. 316), and become 

 functional leaves. 



343. Germination of Indian Corn. Soak kernels of 

 corn. Note that the micropyle and hilum are at the 

 smaller end. (Fig. 317.) Make a longi- 

 tudinal section through the narrow 

 diameter; Fig. 318 shows it. The 

 single cotyledon is at a, 

 the caulicle at 

 plumule at p, 

 cotyledon remains in 

 the seed. The food is 

 stored both in the cotyledon and as endosperm, chiefly the 

 latter. The emerging shoot is the plumule, with a sheathing 



319. Indian corn. Cau- 

 licle at c ; roots emerg- 

 ing at 7n; plumule at p. 



6, the 

 The 



320. Indian corn. o. plumule; 

 n to p, epicotyl. 



