204 A Defence of Menders 



revolution it might be possible for a future experimenter to 

 conclude that Pisum sativum was by nature a "mosaicized" 

 species in these respects, though the mosaic character may 

 have arisen once in a seed or two as an exceptional 

 phenomenon. When the same reasoning is extended to 

 wild forms depending on other agencies for selection, some 

 interesting conclusions may be reached. 



But in Mendelian cases we are concerned primarily not 

 with the product of gametes of blended character, but with 

 the consequences of the union of gametes already dis- 

 continuously dissimilar. The existence of pure Mendelian 

 gametes for given characters is perfectly compatible with 

 the existence of blended or mosaic gametes for similar 

 characters elsewhere, but this principle enables us to form 

 a comprehensive and fruitful conception of the relation of 

 the two phenomena to each other. As I also pointed 

 out, through the imperfection of our method which does 

 not yet permit us to see the differentiation among the 

 gametes though we know it exists, we cannot yet as a 

 rule obtain certain proof of the impurity of the gametes 

 (except perhaps in the case of mosaics) as distinct from 

 evidence of imperfect dominance. If however the case be 

 one of a "mule" form, distinct from either parent, and 

 not merely of dominance, there is no a priori reason why 

 even this may not be possible ; for we should be able to 



of peas (Jour. R. Hort. Soc. xxir. 1899, p. 254) alludes to the great 

 instability of this class of pea. To Laxton, he says, " we are indebted 

 for a peculiar type of Pea, a round seed with a very slight indent, the 

 first of this class sent out being William the First, the object being to 

 get a very early blue- seeded indented Pea of the same earliness as the 

 Sangster type with a blue seed, or in other words with a Wrinkled Pea 

 flavour. This type of Pea is most difficult to keep true on account of 

 the slight taint of the Wrinkled Pea in the breed, which causes it to 

 run back to the Bound variety." 



