272 BREEDING 



had happened, the way for Mendelian segregation 

 was made clear by the possibility of a union between 

 two DKs. A female cannot mate with a female ; 

 but a yellow can mate with a yellow. 



The only alternative to this view of the origin of 

 the Mendelian phenomena is the supposition that 

 the first types to originate were the pure dominant 

 and recessive homozygous forms. Now, apart from 

 the fact that this is rendered improbable by the 

 probability of the common origin of the MendeHan 

 and sexual modes of inheritance from a mode which 

 most closely resembles, even if it difiers from, the 

 sexual one, it can be shown that at least in one case 

 this cannot have been the way in which these pheno- 

 mena arose. And it is well to remember that the 

 question we have to ask ourselves when we are 

 considering the value of evidence for a particular 

 theory is not : how many facts are consistent with 

 it ? but : is there a single one which is inconsistent with 

 it ? The statements of forty of the friends of the 

 Irishman who was accused of shooting his landlord, to 

 the effect that they had not seen him doing it, were 

 consistent with his statement that he had not done it. 

 But he was hanged, because the fact that one man had 

 seen him do it was not consistent with his statement. 



One of the varieties of the Snapdragon, which 

 ordinarily has green leaves, is a form with much 

 yellower, variegated, leaves; this variety is spoken 

 of as aurea (golden). The inheritance of these 

 characters has been investigated by Dr. Baur. He 

 found that the greens bred true but that the varie- 



