WHITE— STUDIES OF INHERITANCE IN PISUM. 



523 



breeding true, indefinitely, while the impure yellows in each genera- 

 tion continue to give rise to yellows and greens in the ratio of 3:1. 

 Darbishire has followed this study through to the Fj^ or F^o genera- 

 tion and finds nothing to controvert this statement. The yellow and 

 green seeds that came from such a cross appear to be the same sort 

 of colors that the grandparental ancestors had. The tendency of 

 yellows to be greenish because of immaturity, and of greens to fade 

 is no more marked in the progeny than in their pure forbears. 



The actual results from crossing pure yellow and green coty- 

 ledon plants are given in the following table :^ 



Mendel (60) tested out 519 Fo yellows by growing an Fo, the 

 result being: 353 seeds gave yellow and green seeds (3:1), 166 

 seeds gave only yellow seeds, the ratio of the former to the latter 

 being 2.13 : i. 



Darbishire (21) tested out in the same manner 140 F2 yellows, 

 which in Fo gave : 98 Fo seeds with both yellow and green progeny, 

 42 ¥., seeds with only yellow progeny, the proportions being 2.2 : i. 



Back-crosses (56) of F^ or of similar heterozygous plants from 

 later generations with the yellow parent gave all yellow as follows : 



Mendel, 192 yellow :o green, 



Tschermak, 126 yellow :o green. 



2 These data are taken from Darbishire (21) and White (98). 



