NATURE OF FOOD STORED IN SEEDS 15 



times called the bran layer. The two layers of cells (s, s t ) are the 

 two seed coats (the outer and the inner seed coats. See the for- 

 mation of the seed, paragraph 305.) At p is the aleurone layer, 

 the cells containing proteid grains, and at st are the starch con- 

 taining cells. 



19. 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 content. 

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

 cells are proteid grains or aleurone grains. These proteids form 

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

 layer is rich in nitrogenous food, the proteids being a nitro- 

 genous substance containing nitrogen (N), carbon (C), hydro- 

 gen (H), oxygen (O), sulphur (S) and sometimes 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 proteids are in composition very much like the albumen, 

 or white of egg. 



20. 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, C, H, and O.* 

 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. 



21. 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 

 plants. Commercial starch, while it will give the reactions for 

 starch, is not suitable for the study of the grains, since they are 

 destroyed in its preparation. Starch becomes blue by treat- 

 ment with a few drops of a tincture of iodine, or, better, a solu- 

 tion of iodine in potassium iodide. Sometimes the color is more 



* C 8 H 10 6 . 



