182 



ELEMENTARY STUDIES IN BOTANY 



root anchorage holds and the cotyledons are pulled out of 

 the seed-coat, and when they are free from it the hypocotyl 

 straightens. The significant fact in this escape is not that 

 the cotyledons are pulled out, for in many seeds they remain 

 within the seed-coat, but that the plumule is pulled out, for 



it develops the stem 

 and leaves. 



This is only one 

 method by which 

 the plumule be- 

 comes free, but it 

 is a common way, 

 and will suggest the 

 interpretation of 

 other methods that 

 ought to be ob- 

 served. For ex- 

 ample, in the scar- 

 let-runner bean the 

 cotyledons are not 

 usually freed from 

 the testa, the first 

 joint of the stem 

 (in the plumule) 

 developing the arch 

 and freeing the 

 stem-tip and leaves, 



FIG. 1 50. Germination of corn, showing superficial 



position of embryo, the unfolding leaves, and the aS may DC S66n in 



roots; the single cotyledon is not seen, remain- . e pr ip cihnwn in 



ing in close contact with the endosperm. trie SCriCS SnOWn in 



Figs. 147 and 148. 



Such seeds as those of peas, castor-bean, squash, and 

 corn should be germinated to show important variations. 

 In the pea and acorn, for example, the cotyledons are gorged 

 with food and are never freed from the testa, but the plumule 

 is liberated by the elongation of the bases of the cotyledons 



