LUTHER BURBANK 



few cases of the fertility of seeming hybrids might 

 best be explained either on the supposition that the 

 observed forms were not really of the parentage 

 ascribed to them; or else that the parent forms, 

 even though classified as different, were not really 

 entitled to rank as independent species. 



In a word, the doctrine of Kolreuter and his 

 followers, which would make the sterility of the 

 hybrid offspring a test of the specific diversity of 

 the parent forms, was perhaps the stock doctrine 

 of the biological world. 



The implications of such an argument are obvi- 

 ous. If we are to answer the question, "What is 

 the test as to whether two forms are entitled to 

 recognition as different species?" by saying, "They 

 are different if their hybrid offspring are sterile, 

 and they are only varieties if their offspring are 

 fertile" — we should obviously supply a definition 

 that takes the matter beyond the range of 

 argument. 



And, inasmuch as the minds of the biologists 

 were now adjusted to the new Darwinian idea that 

 there is a wide range of variation in natural forms, 

 and that natural species are after all only varieties 

 that have separated a little farther, the idea that 

 the classifier might be mistaken in ascribing spe- 

 cific difference to any pair of forms, and that the 

 physiological test of the production of sterile 



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