1 24 PLANT-BREEDING 



deposited on the silk. In close proximity this number will 

 often surpass that of the normal kernels, and by artificial 

 cross-pollination all the kernels on an ear of sweet corn may 

 be induced to become starchy. It is a simple method of 

 measuring the degree of transportation of pollen by the 

 wind, and wherever a field of sweet corn is near a culture of 

 dent corn, the inspection of the ears may give us an idea of 

 the significance of this transportation. 



All the starchy kernels on a partly cross-pollinated ear of 

 sweet corn have hybrid germs, since they were fertilized by the 

 contents of the same pollen tube as the endosperm. By this 

 means the hybrid kernels may be recognized and eliminated 

 in such cases, and thus the strains of sweet corn are easily 

 kept pure of admixtures of this kind. 



This wind-pollinated condition of corn has a great influ- 

 ence on the process of selection. In other cereals, whenever 

 a single head has been selected in the field, it is almost sure 

 to be exclusively self-fertilized and its progeny will at once 

 yield a pure and uniform race. 



In corn, however, a selected ear will almost always be 

 partly cross-fertilized, and probably by the pollen of more 

 than one of its neighbors. If we could eliminate these hybrid 

 kernels and sow only the self-pollinated seeds, we might ex- 

 pect to get at once a pure and uniform race, which would need 

 only careful protection against foreign pollen during the first 

 year of its multiplication. There can be hardly any doubt 

 that this conclusion, drawn from the other cereals, would 

 hold good for corn also. At present, however, it is impos- 

 sible to distinguish the cross-fertilized kernels of an ear from 

 the self -pollinated seeds, except in such extreme cases as we 

 have just alluded to. The only way is to sow all the seeds, 

 and to judge the plants when growing. In some instances 

 the hybrids may be recognized and thrown out before tassel- 

 ing, but ordinarily they will have to stand in the field until 



