LUTHER BURBANK 



the environment by supplying new forms that 

 come in competition with the ones already 

 developed. 



LIMITS OF HYBRIDIZING 



But why then, you will perhaps ask, does not 

 the production of new forms between natural 

 species take place so universally as to disturb the 

 entire scheme of organic nature. In point of fact, 

 the zoologist and the botanist are able to describe 

 vast numbers of species, each of which has certain 

 fairly well-defined characteristics and differs in 

 certain definite regards from other forms. 



It is true that the more closely the matter is 

 studied the more commonly varieties are found 

 that manifest characteristics intermediate between 

 those of the supposedly fixed species. But even 

 when these are taken into consideration, it still 

 remains true that the word "species" as applied 

 to a vast number of familiar forms of vegetable 

 and animal life, has a pretty definite and tangible 

 meaning. 



How is this possible, if the interbreeding of 

 species is a universal phenomenon? 



The answer is found in the facts (1) that the 

 hybrid forms produced when species in nature 

 are crossed, for the most part quickly disappear 

 because they are not an improvement, from the 

 standpoint of adaptation to their environment, 



[36] 



