194 A Defence of Menders 



and others like them have been a stumbling-block to all 

 naturalists. Of such paradoxical phenomena Mendel now 

 gives us the complete and final account. Will Professor 

 Weldon indicate how he proposes to regard them? 



Let me here call the reader's particular attention to 

 that section of Mendel's experiments to which Professor 

 Weldon does not so much as allude. Not only did Mendel 

 study the results of allowing his cross-breds (DR's) to 

 fertilise themselves, giving the memorable ratio 



IDD : 2DR : IRR, 



but he fertilised those cross-breds (DR's) both with the 

 pure dominant (Z>) and with the pure recessive (R) 

 varieties reciprocally, obtaining in the former case the ratio 



IDD : IDR 



and in the latter the ratio 



IDE : IRR. 



The DD group and the RR group thus produced giving 

 on self-fertilisation pure D offspring and pure R offspring 

 respectively, while the DR groups gave again 



IDD : 2DR : I RR. 



How does Professor Weldon propose to deal with these 

 results, and by what reasoning can he suggest that 

 considerations of ancestry are to be applied to them? 

 If I may venture to suggest what was in Mendel's mind 

 when he applied this further test to his principles it 

 was perhaps some such considerations as the following. 

 Knowing that the cross-breds on self-fertilisation give 



IDD : 2DR : I RR 

 three explanations are possible : 



