392 W. Bateson. 



Reversion and Tariatiou. 



One of the most interesting- deductions from these facts is that 

 which concerns the nature of reversion on Crossing, a phenomenon 

 the importance of whicli was first insisted on by Darwin. We 

 now recognize that such reversion is due to the meeting- of long- 

 parted complementary factors. Conversely it is clear that the original 

 variation which gave rise to the types whose cross brings about the 

 reversion, must have consisted in the separation of those factors. 

 Such facts naturally raise a question of vast consequence in evolution. 

 The variation which, for instance, i)roduced the red flowered Sweet 

 Pea from the purple was essentially an elimination of the blue 

 factor. The variation which produced a white Sweet Pea is most 

 simply described as an elimination of one of the colour-factors. Is 

 it not then possible that such analytical variations, as we may call 

 them, are responsible for much of the diversity of nature? In dis- 

 cussing the phenomenon of dominance reference was made to the 

 difficulty of distinguishing, in the present state of ph3'Siological 

 knowledge, between characters which are positive and those which 

 are negative. Not until some certaintj^ is reached regarding this 

 very material point can we even feel perfect confidence that variation, 

 in general, may not be an analytical process, and evolution itself a 

 passage from a higher to a lower degree of complexity. I hope that 

 reference to such a question may not lay me open to a charge of 

 premature speculation. I have no bias in favour either of a positive 

 or a negative answer, but it is impossible to study the modern develop- 

 ments of genetics without becoming aware that such a question exists. 



Colour-heredity in general. 



As will be now understood, the phenomena of colour-inheritance 

 are so complex that it is not easy to give a list of cases like those 

 previously recited. Some references however will be acceptable, but 

 in almost all the cases quoted further annotation is required. In 

 particular, it is to be observed that where the interaction between 

 several factors occurs, the term "dominant"' and "i-ecessive" are no 

 longer strictly applicable. These terms can only be properly used 

 to describe the relationship between nembers of the same allelo- 

 morphic pair. Phenomena following the general lines of those dis- 

 cussed above have been observed in the following cases. 



