124 A Defence of Mendel's 



In respect of shape the seeds of a variety otherwise 

 stable are as a rule fairly uniform, the co-existence of 

 both shapes and of intermediates between them in the 

 same variety is not infrequent. As Professor Weldon has 

 said, Telephone is a good example of an extreme case of 

 mixture of both colours and shapes. William I. is another. 

 It may be mentioned that regular dimorphism in respect 

 of shape is not so common as dimorphism in respect 

 of colour. Of great numbers of varieties seen at Messrs 

 Suttons' I saw none so distinctly dimorphic in shape as 

 William I. which nevertheless contains all grades commonly. 



So far I have spoken of the shapes of ordinary English 

 culinary peas. But if we extend our observations to the 

 shapes of large-seeded peas, which occur for the most part 

 among the sugar-peas (mange-touts), of the "grey' peas 

 with coloured flowers, etc., there are fresh complications 

 to be considered. 



Professor Weldon does not wholly avoid these (as 

 Mendel did in regard to shape) and we will follow him 

 through his difficulties hereafter. For the present let me 

 say that the classes round and wrinkled are not readily 

 applicable to those other varieties and are not so applied 

 either by Mendel or other practical writers on these 

 subjects. To use the terms indicated in the Introduction, 

 seed-shape depends on more than one pair of allelomorphs 

 possibly on several. 



Stability and Variability. 



Generally speaking peas which when seen in bulk are 

 monomorphic in colour and shape, will give fairly true and 

 uniform offspring (but such strict monomorphism is rather 

 exceptional). Instances to the contrary occur, and in my 

 own brief experience I have seen some. In a row of Fill- 



