IN-BREEDING 237 



While the fundamental principles governing the trans- 

 mission of characters are the same in plants and animals, 

 the practical applications are sometimes widely different. 

 Wholesale advice based wholly upon plant investigations, 

 therefore, and intended to guide the practical breeder 

 of animals is not always justified for obvious reasons. 

 The experiments conducted for the purpose of testing 

 the effects of in-breeding on Indian corn (Zea Mays) have 

 been extensive. In every case, so far as the author has 

 been able to determine, in-breeding corn has resulted in 

 decreased yields if long continued. Hayes 1 and East 

 found that " the first generation of in-breeding has the 

 greatest detrimental effect." The injury from in-breed- 

 ing is not continuous, but results in separating the pure 

 lines in a variety. When once a pure line is produced 

 by in-breeding, further in-breeding apparently does not 

 reduce the yield. Shamel 2 found that four generations 

 of self-fertilization of corn so weakened the strain that 

 the seed failed to germinate. Darwin, experimenting 

 with morning glories (Ipomsea) for a period of ten years, 

 found that the strain which was screened so that insects 

 could not bring about cross-fertilization lost in vigor 

 as compared with a similar strain which had beeen left 

 in the open and cross-fertilized through the agency of 

 insects. 



Wheat is a self-fertilizing plant. Unnumbered genera- 

 tions of in-breeding seem not to have decreased its vigor 

 or lowered its fertility. Castle in-bred brother and sister 

 of Drosophila (pomace fly) for 59 generations. No loss 

 of fertility or vigor was observed. 



1 Hayes and East, Bui. 168, Connecticut Agricultural Experi- 

 ment Station, p. 11. 



2 Shamel, U. S. Dept. of Agr., Year Book, 1905, p. 388. 



