174 



GERMINATION 



fixed, and its subsequent growth tends to raise the cotyle- 

 dons above the ground, as in the bean. 



339. When cotyledons rise into the air, germination is 

 said to be epigeal ("above the earth"). Bean 

 and pumpkin are examples. When the hypo- 

 cotyl does not elongate greatly and the coty- 313. Sprouting of 

 ledons remain under castorbean - 

 ground, the germination is hypogeal ("be- 

 neath the earth"). Pea and scarlet run- 

 ner bean are examples. When the ger- 

 minating seed lies on a hard surface, as 

 on closely compacted soil, the hypocotyl 

 and rootlets may not be able to secure a 

 <nK~^S^" foothold and they assume grotesque 



— ' * forms. (Fig. 310.) Try this with peas 



314. Germination of cas- . , 



tor bean. Endosperm ailQ DeanS. 



ata - 340. The first inter- 



node above the cotyledons — between the 

 cotyledons and the plumule — is the epi- 

 cotyl. It elevates the plumule into the air, 

 and the plumule-leaves expand into the 

 first true leaves of the plant. These first 

 true leaves, however, may be very unlike 

 the later leaves. 



341. Germination of Bean. — The 

 common bean, as we have seen (Fig. 

 308), has cotyledons that occupy all 

 the space inside the seed-coats. When 

 the hypocotyl or elongating caulicle 

 emerges, the plumule-leaves have begun 

 to enlarge and to unfold. (Fig. 311.) The 

 hypocotyl elongates rapidly. One end 

 of it is held by the roots. The other is 

 held by the seed-coats in the soil. It, 



Germination complete ,. . . , ■; c , , 



in castor bean. therefore, takes the form 01 a loop, and 



315. Castor bean. En- 

 dosperm at a, a; co- 

 tyledons at 6. 



