LUTHER BURBANK 



plicates the entire situation. The fact of double 

 parentage is one that will be seen at a glance to 

 remove all simplicity from the formula "like pro- 

 duces like." For no two individuals are precisely 

 alike; no two cells of the germ-plasm carry pre- 

 cisely the same ancestral traits. 



The briefest consideration will suggest some, at 

 least, of the complications that necessarily result 

 when more or less divergent germ-plasms are 

 commingled. 



Of course, if two ancestral germ-plasms are 

 too widely divergent they cannot commingle at all. 

 The two organisms are then said to be mutually 

 infertile. This was formerly supposed to be the 

 case with most different species. Indeed, the test 

 of capacity to interbreed with the production of 

 fertile offspring was long considered to be the 

 best test of specific identity. Nowadays we know, 

 thanks largely to Mr. Burbank's experiments, 

 that this test cannot be fully relied upon. Never- 

 theless, it is clear that only species that are some- 

 what closely related can interbreed. 



Even where union takes place between mem- 

 bers of the same species, however, there are sure 

 to be some divergent traits that are more or less 

 in conflict. It may chance even that there are 

 numerous minor traits that are mutually antago- 

 nistic. 



For example, to take the simplest and most 

 familiar case, animals of the same species may 

 differ radically in color. One guinea-pig may be 

 jet black and another pure white. It is obvious, 



[276] 



