128 A Defence of Menders 



(neglecting environment) is the visible expression, has arisen 

 and can arise at one or more points of time, and we have 

 no difficulty in believing it to occur now. In many cases 

 we have clear evidence that it does. Crossing, dare we 

 call it asymmetrical fertilization ? is one of the causes of 

 the production of heterogeneous gametes the result of 

 divisions qualitatively difterentiant and perhaps asym- 

 metrical*. 



There are other causes and we have to find them. 

 Some years ago I wrote that consideration of the causes 

 of variation was in my judgment premature!. Now that 

 through Mendel's work we are clearing our minds as to the 

 fundamental nature of "gametic" variation, the time is 

 approaching when an investigation of such causes may be 

 not unfruitful. 



Of variation as distinct from transmission why does 

 Professor Weldon take no heed ? He writes (p. 244) : 



" If Mendel's statements were universally valid, even among 

 Peas, the characters of the seeds in the numerous hybrid races 

 now existing should fall into one or other of a few definite 

 categories, which should not be connected by intermediate 

 forms." 



Now, as I have already pointed out, Mendel made no 

 pretence of universal statement : but had he done so, the 

 conclusion, which Professor Weldon here suggests should 

 follow from such a universal statement, is incorrectly 

 drawn. Mendel is concerned with the laws of transmission 



* The asymmetries here conceived may of course be combined in 

 an inclusive symmetry. Till the differentiation can be optically 

 recognized in the gametes we shall probably get no further with this 

 part of the problem. 



t Materials for the Study of Variation, 1894, p. 78. 



