10 



THE BOOK OF NATURE STUDY 



and the radicle just ready to push its way through the testa. In 

 fact, the seed of the pea consists practically of the seed-coat and 

 embryo. 



In the grain of wheat, the embryo is very minute and occupies 

 but a small portion of the whole grain. Its position is indicated 

 by the pale patch on the convex surface of the grain. The greater 

 part of the grain consists of a white substance, the endosperm 

 or albumen, which was formed in the ovule as a result of 



FIG. 4. Seedling of wheat. 

 /, primary root. 



FiG. 5. Seedling of onion. 

 The dotted line marks 

 the level of the soil. 



fertilisation. The difference between albuminous and exalbumin- 

 ous seeds is simply this ; in the former the food-material is not 

 absorbed by the embryo, in the latter it is. The embryo is in contact 

 with the endosperm by a shieldlike structure, the scutellum, 

 which probably represents the cotyledon. The scutellum sucks 

 food from the endosperm and hands it on to the young plant. 

 The outer coat of the grain is the wall of the ovary, the seed-coat 

 adheres to it and can only be detected with the aid of a microscope. 

 The plumule of the wheat is curved, but does not form as complete 



