312 FIELD CROPS FOR THE COTTON-BELT 



The greater portion of the wheat grain consists of endo- 

 sperm or starch cell? which form the chief constituent of 

 wheat flour. The ratio of embryo to endosperm is about 

 as one to thirteen. The embryo is 

 composed essentially of two parts, viz., 

 the miniature plant known as the veg- 

 etative portion, and the absorbent 

 organ, known as the scutellum, which 

 on the germination of the seed, trans- 

 fers the substance of the endosperm 

 to the embryo for its nourishment. 

 Surrounding the endosperm and em- 

 bryo is a single layer of aleurone cells 

 known as the aleurone layer, which 

 makes up about eight per cent of the 

 weight of the grain. 



Just outside of and surrounding the 

 aleurone layer is a single layer of col- 

 lapsed cells called the tegmen or nu- 

 cellus. This is in turn surrounded by 

 the testa, which covering contains most 

 of the coloring matter of the grain. 



Fig. 53. — Cross-sec- 

 tion and transverse 

 section of grain of 

 wheat. Below: 

 transverse section 

 of an unripe grain. 



pericarpT (2)^outer This Coloring matter may vary from 

 JTer^St'e^gum^int; '^^^ P^^^^ shades of yeUow through am- 

 ber to a deep red, and gives the grain 

 its characteristic color so often used 

 in the classification of wheat varieties. 

 The three layers above described are inclosed in the 

 pericarp or outside covering, which corresponds to the 

 pod in the pea. The nucellus, testa and pericarp con- 

 stitute what is commonly spoken of as wheat bran. 



The wheat grain is very variable as regards size, color, 

 hardness, shape, weight, and composition, all of these char- 



(4) remains of nu- 

 cellus; (5) aleurone 

 cells; (6) starch 

 cells. 



