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THE AMERICAN NATURALIST [Vol. XLVII 



implications. 20 The custom has grown up (notably in the 

 work of Shull and East) of using the term "inbreeding" 

 when self-fertilization is really meant. I think it would 

 be difficult, in view of the considerations already set forth 

 in detail, to justify this usage on general grounds. In 

 any event it is clear that when the term inbreeding is 

 used in the sense of self-fertilization it is not used in its 

 ordinary sense. The plant-breeder rarely carries out a 

 mating which is strictly comparable with the matings 

 which the animal breeder makes when he inbreeds. The 

 closest inbreeding possible with animals is the continued 

 mating of brother and sister. How often does the plant- 

 breeder make a mating which is objectively exactly this? 

 It is assumed, specifically and implicitly, by the plant- 

 breeder that his method of inbreeding by self-fertilization 

 is equivalent to methods of inbreeding practised in 

 animals. On the basis of that assumption he compares 

 the results in the two cases. Can such a comparison be 

 regarded as a strictly just one, until it has in fact been 

 proven to be so by concrete evidence? I think it can not, 

 because it rests on an assumption which is not only mi- 

 proven, but which, as I have endeavored to show, is con- 

 trary to fact. 



On just this ground, it seems to me, the section of the 

 paper of East and Hayes devoted to an "Extension of 

 the Conclusions to the Animal Kingdom" is weakened. 

 From this section I have been unable to understand 

 precisely what the concept in the minds of these authors 

 as to inbreeding in animals really is. They nowhert 

 sharply define their concept of inbreeding. Throughout 

 the portion of the paper dealing with plants it appears 



