102 BOTANY OF CROP PLANTS 



yellow. The proportions of these colors determine whether 

 the wheat is white, yellow, or red. 



Brown found in Triticum, as well as in Avena, Secale, and 

 Hordeum, that the semi-permeabihty of the grain coats is 

 localized in the testa. It is very probable that the epidermal 

 membrane of the nucellus also has semi-permeable properties. 



Nucellus (perisperm). — The epidermis of the nucellus 

 surroimds the aleurone layer. It is the only remaining 

 portion of the nucellar tissue, which was comparatively large 

 in the undeveloped ovule. The mature nucellus consists of 

 cells with strongly thickened walls, and with indistinct 

 cavities. It is possible that in some cases the nucellus is 

 completely absorbed, and hence wanting in the mature 

 grain. 



Endosperm. — The endosperm consists of two portions, 

 starchy or floury endosperm, and aleurone layer. The endo- 

 sperm constitutes about 92 per cent, of the grain's volume. 

 The cereals are cultivated chiefly for the food material 

 stored in the grain. In all of them, the bulk of this food is 

 found in the endosperm. The chief food materials stored in 

 the endosperm of grains are starch and proteins. The 

 germinating embryo makes use of these foods in the first 

 few days of its growth, or until its roots are taking substances 

 from the soil, and the young leaves are manufacturing food, 

 or, in other words, until the young plant has established its 

 independence. 



Aleurone Layer. — This is a single layer of large cells im- 

 mediately within the nucellus. The cells are rather imi- 

 formly square or rectangular when viewed in transverse or 

 longitudinal section, but irregular in shape when viewed per- 

 pendicular to the surface. They are stored largely with 

 aleurone grains. This layer is often erroneously called the 

 gluten layer. The term "gluten" is only properly applied 



