SEEDS AND CERMLXATION 



^ 





Fir,. 17. — Pea. Grotesque forms assumed 

 when the roots cannot gain entrance to 

 the soil. 



air, germination is said to be epigeal ("above the earth"). 

 Bean and pumpkin are examples. When the hypocotyl 

 does not elongate greatly ,- 



and the cotyledons remain 

 under ground, the germi- 

 nation is hypogeal ("be- 

 neath the earth"). Pea 

 and scarlet runner bean 

 are examples (Fig. 48). 

 When the germinating 

 seed lies on a hard sur- 

 face, as on closely com- 

 pacted soil, the hypocotyl 

 and rootlets may not be able to secure a foothold and they 4^ 

 assume grotesque forms. (Fig. 17.) Try this with peas ^ 

 and beans. 



The first internode (" between nodes") above the coty- 

 ledons is the epicotyl. 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 t — 

 very unlike the later leaves in shape. 



Germination of Bean. — The common bean, as we have 

 seen (Fig. 15), has cotyledons that occupy all the space 

 inside the seed-coats. When the hy- 

 pocotyl, or elongated caulicle, emerges, 

 the plumule-leaves have begun to en- 

 large, and to unfold (Fig. 18). 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 therefore takes the form of a loop, 

 and the central part of the loop " comes up " first (a, Fig. 

 19). Presently the cotyledons come out of the seed-coats, 



Fig. 18. — Cotyledons 

 of Germinating 

 Bean spread apart 

 to show Elongat- 

 ing Caulicle and 

 Plumule. 



