46 



BREEDING CROP PLANTS 



order to illustrate the general results. The theoretical explana- 

 tion is given, as an appreciation of these phenomena is essential 

 in obtaining a correct plant breeding perspective. 



The most extensive studies made have been those with maize. 

 As this crop is almost entirely cross-pollinated under natural 

 field conditions it is an admirable one to contrast with self- 

 fertilized plants. Table VIII presents differences in yield and 

 height obtained at the Connecticut Station with four self-fer- 

 tilized strains of Learning Dent. These strains were grown only 

 in small plots, therefore differences are only indicative of the 

 general results which may be expected. Crosses between in- 

 dividual plants within a strain that had been selfed six or seven 

 years, were not appreciably more vigorous than the progeny of 

 self -fertilized seed. These strains also differ in other characters, 

 such as shape of ear, width of leaf, and color in various organs. 

 One strain of Learning Dent No. 1-12 was self-fertilized for about 

 seven years. It produced well-developed tassels but few ears 

 and was eventually lost. 



TABLE VIII. THE EFFECT OF INBREEDING ON THE YIELD AND HEIGHT OF 



MAIZE 



