20 GROWTH AND WORK OF PLANTS 



sometimes called the bran layer. The two layers of cells (s, s^ 

 are the two seed coats (the outer and the inner seed coats. See 

 the formation of the seed, paragraph 320). At p is the aleurone 

 layer, the cells containing protein grains, and at st are the starch 

 containing cells. 



26. The aleurone layer. Lying just within the seed coats is 

 a single layer of very regular cells rectangular in outline and nearly 

 cuboidal in form. They are packed with fine granular con- 

 tent. This layer of cells is the aleurone layer. The granules in 

 the cells are protein grains or aleurone grains. The proteins 

 form one of the food substances stored in many seeds. The 

 aleurone layer is rich in nitrogenous food, the proteins being a ni- 

 trogenous substance containing nitrogen (N), (see paragraph 172) 

 carbon (C), hydrogen (H), oxygen (O), sulphur (S) and some- 

 times phosphorus (P). This forms the most nutritious part of 

 the flour, and it is well known that nitrogenous foods, both for 

 plants and animals, are much less abundant and more costly 

 than most other foods. These proteins are in composition very 

 much like the albumen, or white of egg. 



27. The starch in the endosperm. Just inside of the aleu- 

 rone layer is a tissue of large angular cells filled with coarse 

 whitish grains. These are starch grains. Starch does not con- 

 tain nitrogen. It consists of three elements, carbon, hydrogen 

 and oxygen.* The starch grains vary greatly in size, and in 

 some plants they are much larger than in others. If the section 

 of a grain of wheat or corn is treated with iodine the starch is 

 stained blue while the aleurone layer is stained brownish yellow. 



28. Starch. Starch is stored in plants usually in the form 

 of grains which are deposited inside the cells. While these 

 grains are microscopic in size, they vary a great deal in different 



which the seed is formed. If this brown layer could be entirely removed 

 from the grain of corn and wheat the remaining part of the grain would be 

 the seed. While then we speak of the grain of corn and wheat as seeds we 

 should remember that this usage is not technically correct, for the walls of 

 the seed capsule are consolidated with those of the seed. 



