354 



GENETICS IN RELATION TO AGRICULTURE 



Collins to be those of Seal (Michigan, 1878-1882), Ingersoll (Indiana, 

 1881), Sanborn (Maine, 1889), and of Morrow and Gardner (Illinois, 

 1892). All of these crosses were made between commercial varieties and 

 in each case the hybrids outyielded one or both parents. Then came the 

 work of Shull and of East (1908) with inbred strains and the crosses between 

 them, both investigators obtaining an increase in yield in the hybrids 

 over that of the original stock. Following this the United States Depart- 

 ment of Agriculture conducted experiments on an increasingly extensive 

 scale and included work with the most distinct types as well as commercial 

 varieties and inbred strains. More recently various experiment stations 

 have conducted similar investigations. 



Crossing inbred strains or biotypes produces the most striking results 

 because the rate of increase in vigor in the F\ hybrids over the inbred 

 strains is enormous (as much as 250 per cent, over the average of the 

 parents). Of course it is much greater in some cases than in others be- 

 cause of the inherent differences between different biotypes. East worked 

 with biotypes of four different varieties and secured an average increase 

 of 73 per cent, in all crosses. The data on inbreeding the Learning 

 dent variety are summarized by East and Hayes in Table LI. It will be 

 noted that two of the strains were not grown as second inbred generations 



TABLE LI. EFFECT OF INBREEDING IN STRAINS OF LEAMING DENT MAIZE 

 Yield in bushels of shelled corn per acre and years in which grown (After East and 



Hayes) 



