120 A Defence of Mendel's 



When he speaks of the "law' or "laws' 3 that he has 

 established for Pisum he is referring to his own discovery 

 of the purity of the germ-cells, that of the statistical 

 distribution of characters among them, and the statistical 

 grouping of the different germ -cells in fertilization, and 

 not to the " Law of Dominance " which he never drafted 

 and does not propound. 



The issue will be clearer if I here state briefly what, as 

 far as my experience goes, are the facts in regard to the 

 characters cotyledon-colour and seed-shapes in peas. I have 

 not opportunity for more than a passing consideration of 

 the seed- coats of pure forms * ; that is a maternal character, 

 a fact I am not sure Professor Weldon fully appreciates. 

 Though that may be incredible, it is evident from many 

 passages that he has not, in quoting authorities, considered 

 the consequences of this circumstance. 



The normal characters: colour of cotyledons 

 and seed-coats. 



Culinary peas (P. sativum, omitting purple sorts) can 

 primarily be classified on colour into two groups, yellow 

 and green. In the green certain pigmentary matters 

 persist in the ripe seed which disappear or are decomposed 

 in the yellow as the seed ripens. But it may be observed 



* The whole question as to seed-coat colour is most complex. 

 Conditions of growth and ripening have a great effect on it. Mr 

 Arthur Sutton has shown me samples of Ne Plus Ultra grown in 

 England and abroad. This pea has yellow cotyledons with seed-coats 

 either yellow or "blue." The foreign sample contained a much 

 greater proportion of the former. He told me that generally speaking 

 this is the case with samples ripened in a hot, dry climate. 



Unquestionable Xenia appears occasionally, and will be spoken of 

 later. Moreover to experiment with such a pfonf-character an extra 

 generation has to be sown and cultivated. Consequently the evidence 

 is meagre. 



