ON CORN BREEDING 



123 



this phenomenon. In these cases 

 the effects may be observed di- 

 rectly on the ears, without await- 

 ing the next generation. This 

 is due to the phenomenon known 

 as double fertihzation and which 

 has been discovered only lately. 

 The endosperm, in order to devel- 

 op, must be fcrtihzed as well as 

 the germ, and this is brought 

 about by the tubes of the pollen 

 grains carrying each two male 

 elements or cells, one destined for 

 the germ and the other for the 

 endosperm. Hence we see that 

 in cross-poULnizing the endo- 

 sperm assumes a hybrid nature 

 as well as the germ. In ordinary 

 cases this condition docs not be- 

 tray itself by any visible mark. 

 In crossing sweet corn with dent 

 or Hint corn, the hybrid endo- 

 sperm assumes the characters of 

 the male parent. Thus, when an 

 ear of sweet corn is partly fertil- 

 ized by a dent corn, we shall find 

 on it, after ripening, some starchy 

 kernels among the wrinkled and 

 translucent majority. It is evi- 

 dent that the number of these 

 aberrant kernels will correspond 

 to the number of threads in the silks which are thus cross- 

 poUinated, and the number of the differing kernels is to be 

 considered a direct measure of the proportion of ahen pollen 



Fig. 36. Sweet com, with 

 scattered starchy kernels, pro- 

 duced by partial cross-pollina- 

 tion. 



