62 MAINE AGRICULTURAL EXPERIMENT STATION. I904. 



of the kernel, the bran, designed to protect the softer inner por- 

 tions. These three divisions and their relative proportions are 

 conveniently shown below. 



1. Germ or embryo, 6 per cent of the wheat kernel. 



2. Endosperm or floury part, 82 to 86 per cent of the wheat 

 kernel. 



3. Bran or coverings (not including the aleurone layers), 8 to 

 9 per cent of the wheat kernel. 



To these divisions should be added the aleurone layer, making 

 up 3 or 4 per cent of the kernel. Although this layer is botan- 

 ically a part of the endosperm, it is more convenient, as shown 

 below, to consider it by itself. 



Figure 9 shows the divisions named, and also the position of 

 the brush. 



Chemical analysis shows that the germ is not only rich in oils 

 and mineral constituents, but contains also a large proportion of 

 nitrogenous matter. Since we have no reason for supposing 

 that these nutrients are any less digestible than those furnished 

 by the endosperm, it may be asked why the germ should not be 

 included in the flour. To this it may be replied that the germ is 

 dark in color and the flour containing it would not make an at- 

 tractive loaf. Perhaps a better reason for the exclusion of the 

 germ lies in the readiness with which the oils absorb oxygen 

 from the air, thus becoming rancid and imparting a disagreeable 

 flavor to the flour. Since this change comes about slowly, this 

 objection would not extend to flours which are used within a 

 few months after milling. 



The endosperm, as has been said, is the only part of the kernel 

 which enters the higher grades of flour. It contains all the 

 starch and all the gluten of the wheat. True gluten is found 

 only in wheat and gives this grain its preeminence over the other 

 cereals. On this account its distribution in the kernel is a matter 

 of importance. The outer part of the endosperm differs radi- 

 cally from the inner parts, consisting of nearly square cells filled 

 with a granular form of protein known as aleurone. However 

 valuable this aleurone may be as a food, it should not be con- 

 founded with the gluten, which is found only in the interior of 

 the endosperm. This outer layer of cells is properly known as 

 the aleurone layer, and the name "gluten layer" sometimes given 

 to it is a misnomer. In the processes of the manufacture of fine 



