INHERITED SEED-CHARAGTERS 65 



the seed-coats (which may be grey or white) are not 

 developed till the plant is mature, whilst the cotyle- 

 dons (which may be yellow or green) are among the 

 first parts of the plant to be developed. 



I have been at pains to make this point clear, 

 partly because I am concerned to bring the actual 

 facts discovered by Mendel home to the reader, and 

 partly because the cotyledon characters of Pisum are 

 the most valuable that I know for illustrating the 

 Mendelian phenomenon and for testing the truth of 

 general statements made with regard to it. For it 

 must be plain already that one of the features by 

 which the Mendelian phenomenon may be recognised, 

 when it occurs in a breeding experiment, is the definite - 

 ness of the ratios in which the parental characters 

 reappear or segregate in the second hybrid generation. 

 It is therefore desirable, in critical experiments of 

 this kind, to use material which will furnish the 

 maximum number of individuals at a minimum 

 expense, and in a minimum space. That end is 

 attained by selecting characters, to experiment with, 

 which appear as early as possible in the life history 

 of the animal or plant which bears them, and this 

 condition is better fulfilled by the characters of 

 the cotyledons of Pisum than by any other that I 

 know. A plot of land fifteen yards square will 

 bear 100,000 seeds. 



The actual numbers which Mendel himself obtained 

 in his experiments with the colour of the cotyledons 

 are as follows : He made fifty-eight crosses on ten 

 plants ; and found the yellow colour of the cotyledon 



