BBITISH ASSOCIATION. 313 



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 Antirrhinum so totally unlike each other as majus 

 and molle can be hybridized, as Baur has shown, without a sign of 

 impaired fertility ? Jordan was perfectly right. The true-breeding 

 forms which 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 considerations 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 innu- 

 merable mongrels between them, are what he . finds when he 

 examines any so-called variable type. On analysis the semblance 

 of variability disappears, and tbe illusion is shown to be due to 

 segregation and recombination of series of factors on pre- determined 

 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 variation 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 

 cannot often actually prove variation by loss of factor to be a real 

 phenomenon. 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 

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

 individuals, gives off, as it did a few years since, a salmon-coloured 

 variety, " Coral King," we might claim this as a genuine example of 

 variation by loss. The new variety is a simple recessive. It differs 

 from " Crimson King " only in one respect, the loss of a single 

 colour-factor, and, of course, bred true from its origin. To account 

 for the appearance of such a new form by any process of crossing is 

 exceedingly difficult. From the nature of the case there can have 

 been no cross since "Crimson King" was established, and hence the 

 salmon must have been concealed as a recessive from the first origin 

 of that variety, even when it was represented by very few individuals, 

 probably only by a single one. Surely, if any of these had been 

 heterozygous for salmon this recessive could hardly have failed to 

 appear during the process of self-fertilisation by which the stock 

 would be multiplied, even though that selfing may not have been 

 strictly carried out. Examples like this seem to me practically 

 conclusive." They can be challenged, but not, I think, successfully. 

 Then again in regard to those variations in number and division of 

 parts which we call meristic, the reference of these to original cross- 

 breeding is surely barred by the circumstances in which they often 

 occur. There remain also the rare examples mentioned already in 



* The numerous and most interesting "mutations" recorded by Pro- 

 fessor T. H. Morgan and his colleagues in tbe fly, Drosophila, may also be 

 cited as unexceptionable cases. 



Zool. 4th ser. vol. XVIII., August, 1914. 2 b 



