242 THE BREEDING OF ANIMALS 



225. Results of in-breeding vary with different species. 

 The varying opinions regarding the benefits or injuries 

 from in-breeding may in part be accounted for from the 

 fact that investigators have based their conclusions upon 

 data gathered from researches on widely differing species 

 of animals and plants. The effects of in-breeding are quite 

 different in different species or families. Among plants, 

 nature seems to have designed some species especially to 

 insure cross-fertilization and to guard against self-fertili- 

 zation, while other species are self-fertilizing. Indian 

 corn (Zea Mays) is a good example of the former class 

 of plants. The results of continuous in-breeding on the 

 maize plant are markedly injurious. Shull found that 

 continual self-fertilization in Indian corn resulted in a 

 loss of vigor. There are other plants like wheat that are 

 self -fertilizing, and it is difficult to see how in-breeding 

 can be injurious in such species. 



