370 ANiSrUAL EEPOBT SMITHSONIAN INSTITUTION, 1915. 



introduced, there will be a profusion of forms, utterly unlike each 

 other, distinct also from the original parents. Many of these can 

 be bred true, and if found wild would certainly be described as good 

 species. Confronted b}' the difficulty I have put before you, and 

 contemplating such amazing polymorphism in the second generation 

 from a cross in Antirrhinum, Lotsy has lately with great courage 

 suggested to us that all variation may be due to such crossing. I do 

 not disguise m}^ sj^mpathy with this effort. After the blind compla- 

 cency of conventional evolutionists it is refreshing to meet so frank an 

 acknowledgment of the hardness of the problem. Lotsy's utterance 

 will at least do something to expose the artificiality of systematic 

 zoology and botany. Whatever might or might not be revealed by 

 experimental breeding, it is certain that without such tests Ave are 

 merely guessing when we profess to distinguish specific limits and 

 to declare that this is a species and that a variety. The only defin- 

 able unit in classification is the homozygous form which breeds true. 

 When we presume to say that such and such differences are trivial 

 and such others valid, we are commonl}^ embarking on a course for 

 which there is no physiological warrant. "Wlio could have foreseen 

 that the apple and the pear — so like each other that their botanical 

 differences are evasive — could not be crossed together, though species 

 of Antirrhbium so totally unlike each other as majus and 7)ioUe can 

 be hybridized, as Baur has shown, without a sign of impaired fer- 

 tility ? Jordan was perfectly right. The true-breeding forms Avhich 

 he distinguished in such multitudes are real entities, though the great 

 systematists, dispensing with such laborious analysis, have pooled 

 them into arbitrary Linnean species, for the convenience of collectors 

 and for the simplification of catalogues. Such pragmatical consid- 

 erations may mean much in the museum, but with them the student 

 of the physiology of variation has nothing to do. These " little 

 species," finely cut, true breeding, and innumerable mongrels between 

 them, are what he finds Avhen he examines an}^ so-called variable type. 

 On analysis the semblance of variability disappears, and the illusion 

 is shown to be due to segregation and recombination of series of 

 factors on predetermined lines. As soon as the " little species " are 

 separated out they are found to be fixed. In face of such a result 

 we may well ask with Lotsy, Is there such a thing as spontaneous 

 A'ariation anywhere? His answer is that there is not. 



Abandoning the attempt to show that positive factors can be added 

 to the original stock, we have further to confess that we can not 

 often actually prove vaiiation by loss of factor to be a real phenom- 

 enon. Lotsy doubts whether even this phenomenon occurs. The 

 sole source of variation, in his view, is crossing. But here I think 

 he is on unsafe ground. When a well-established variety like " Crim- 

 son King" Primula, bred by Messrs. Sutton in thousands of in- 



