152 PLANT-BREEDING 



Until now I have almost exclusively considered the 

 selection of corn for yield. But since Hopkins has dis- 

 covered that definite chemical constituents of the grains 

 can be improved also, the selection of corn for special pur- 

 poses has gained a noticeable significance. Of course, 

 the augmentation of the yield of shelled corn per acre will 

 always be the main care of the farmer, but the glucose 

 factories and the hominy mills will pay a higher price for 

 corn that has been improved according to their special 

 industrial interests. 



In order to understand how this aim is reached, we must 

 first consider the structure of the kernels and the relative 

 proportions of their different parts. The kernel consists of 

 the germ or chip and the endosperm, enveloped by a very 

 tliin covering called the hull. The endosperm consists 

 of the starchy and the horny parts; its outer layer, of the 

 thickness of one cell, is the glutinous tissue, which may be 

 considered as an inner covering and is usually much tliicker 

 than the hull. The size of the germ and the relative pro- 

 portion of the starchy and horny parts of the endosperm 

 constitute most valuable varietal characters. In the starchy 

 endosperm the tissue surrounding the germ at the tip end of 

 the kernel is called the tip starch, the name of crown starch 

 being given to the starchy tissue at the upper end. These 

 parts are different in their chemical constitution. The oil 

 is mainly produced in the germ, and the protein mainly in 

 the horny endosperm. The better developed these two 

 parts are the richer the kernel will be in oil or in protein. 

 The germ contains 35 to 40 per cent of oil or from 80 to 85 

 per cent of the. total oil content of the kernel. The horny 

 endosperm contains much starch and about 10 per cent of 

 protein, a figure which is variable according to the varieties 

 tested. 



From this description it is easily seen that a selection 



