ENTIRE WHEAT FLOUR. 63 



white flour, the aleurone layer is rejected from the flour and is 

 included in the waste products. The middle of the endosperm 

 is softer than the outer parts, being richer in starch and poorer in 

 gluten. If ground by itself, it would make an inferior grade of 

 flour. From the center outward, the proportion of gluten grad- 

 ually increases, the largest amount being found in that part of 

 the kernel which lies just within the aleurone layer. 



The term "bran," as ordinarily employed, includes all the por- 

 tions of the grain removed in the milling processes. It is here, 

 however, used with a restricted meaning, and includes only the 

 wheat coverings lying outside the aleurone layer, and does not 

 include the germ. The different parts of the bran vary greatly 

 in composition and this has led to a close study of the coverings 

 of the wheat berry, the general results of which follow. 



The seeds of all our common agricultural plants are borne 

 within a cavity called the ovary. As the seed matures, the ovary 

 usually opens and the seed is discharged. In the grass family, 

 to which the cereals belong, we find an exception to this rule. 

 Here the ovary does not open to release the ripened seed, but be- 

 comes so closely adherent to the seed that a sharp separation is 

 impossible. Perhaps this may be made clearer if we suppose a 

 common garden bean (seed) growing until it entirely fills the 

 pod (ovary), to which it finally becomes so closely cemented that 

 the bean cannot be shelled. 



The wheat kernel, then, consists of a seed still enclosed within 

 the ovary walls. This fact will help to explain the complexity of 

 the wheat coverings, or bran, as the word is here used. The 

 ovary walls constitute what is known to the botanist as the peri- 

 carp. In the immature kernel this is found to consist of three 

 distinct layers, the outer of which, the epidermis, bears the small 

 tuft of hairs sometimes called the brush. Within the pericarp 

 are the true seed coatings, consisting also of several layers, the 

 two outer making up the episperm, while the inner is termed the 

 perisperm. 



This may be summed up as follows : 



Pericarp (walls of j Made up of three layers of cells, the outer of which, the epi- 

 the ovary), ( dermis, carries the brush. 



True seed coatings { ?g^SSi° f tW ° layeM " 



7 



