THE STRUCTURE OF SEEDS 



35 



Near the hilum is a tiny opening (micropyle), and toward this 

 there sometimes extends a ridge which shows the location of the 

 hypocotyl, which will emerge here on germination. 



The tegumen is very thin and often cannot be separated from 

 the testa. 



The Bean. Internal Structure. On removing the seed coats, 

 the kernel is seen to consist of the embryo only, the endosperm 

 having been completely ab- 

 sorbed. All the nourishment 

 is now stored in the cotyle- 

 dons which are large, not at 

 all leaf-like, and contain 

 much proteid and starch. 



The hypocotyl is seen as a . 

 linger-like projection, fitting 

 into a protective pocket in 

 the seed coats. To it the 

 cotyledons are attached on 

 either side. 



By removing one " half " 

 (cotyledon) of the bean, the 

 plumule is exposed, attached 

 to the hypocotyl above the 

 cotyledons and closely pack- 

 ed in between their ends. It 

 is fairly well developed and 

 can be seen to consist of two 

 small leaves, with well-mark- ( 



FIG. 5. Structure of bean, exterior; 



ed veins, folded over each 



with seed coats removed ; with one cotyl- 

 edon removed. 



Other. 



It will be noted that the 

 upper end of the hypocotyl is the one point where all three parts 

 of the embryo are united. When the cotyledon is removed, a scar 

 showing its place of attachment is left on the side of the hypocotyl. 



The pea seed shows a structure similar to that of the bean 

 except that the cotyledons are so enormously swelled with stored 



