152 A Defence of MendeVs 



As Tschermak writes ((37), p. 658), experience has 

 shown him that cross-bred seeds with character transitional 

 between "round" and "wrinkled" behave as hybrids, and 

 have both wrinkled and round offspring, and he now reckons 

 them accordingly with the round dominants. 



Note further the fact that Rimpau found the wrinkled 

 form came true in the fifth year, while the round gave at 

 first more, later fewer, wrinkleds, not coming true till the 

 ninth year. This makes it quite clear that there was 

 dominance of the round form, but that the heterozygotes 

 were not so sharply distinguishable from the two pure 

 forms as to be separated at once by a person not on the 

 look-out for the distinctions. Nevertheless there was 

 sufficient difference to lead to a practical distinction of 

 the cross-breds both from the pure dominants and from 

 the pure recessives. 



The Telephone case may have been of the same nature ; 

 though, as we have seen above, this pea is peculiar in its 

 colour-heredity and may quite well have followed a different 

 rule in shape also. As stated before, the wrinkled off- 

 spring were not cultivated after the third year, but the 

 round seeds are said to have still given some wrinkleds in 

 the eighth year after the cross, as would be expected in a 

 simple Mendelian case. 



(b) Tschermak's cases. The cases Professor Weldon 

 quotes from Tschermak all relate to crosses with Telephone 

 again, and this fact taken with the certainty that the 

 colour-heredity of Telephone is abnormal makes it fairly 

 clear that there is here something of a really exceptional 

 character. What the real nature of the exception is, and 

 how far it is to be taken as contradicting the " law of 

 dominance," is quite another matter. 



