546 



BOTANY OF THE LIVING PLANT 



It is important as a basis for judgment of the results of milling to 

 know by analysis the distribution of the constituent substances in the 



FIG. 447- 



Part of a section of a grain of Wheat. p= pericarp; t= seed-coat, internal to 

 which is the endosperm; a/=aleurone grains; am = starch grains; n= nucleus. 

 ( x 240.) (After Strasburger.) 



Wheat-Grain. This is shown by the subjoined table, taken from Dr. 

 Hutcheson's book on Food : 



A large portion of the grain (85 per cent.) is endosperm ; the bran 

 amounts to 13-5 per cent., and the germ only to 1-5 per cent. The 

 latter is, however, important, for it contains a high proportion of 

 proteids, of fats, and of ash. Since the germ flattens in roller- 

 milling, it can be sifted out. The highly nitrogenous and fatty body 

 thus extracted may then be added to ordinary flour in varying 

 proportions, giving different kinds of germ-bread. Bran is charac- 

 terised by its large proportion of cellulose and lignin (18 per cent.), 

 which is indigestible by man, but more available for herbivorous animals. 

 There is in it, however, a large quantity of nitrogenous substance, owing 

 to the adherence of the aleurone-layer of the endosperm to the flaky 

 scales of the fruit-coat ; the silica in the latter accounts for the large 

 percentage of ash in bran (6 per cent.). Thus bran contains an undue 

 proportion of proteids in which the grain as a whole is deficient. Its 

 value in bran-mash for horses is therefore easily understood. The 



