05Z THE AMERICAN NATURALIST [Vol.L 



from pedigree 1311, belong to the F 2 generation. Taking 

 these plants alone, we have the data given in Table II. 



It is seen at once that there is again the same relative 

 excess of 0. F. Y. E. over I. Y. E. that is shown by the 

 complete data in Table I. The expectation on the 2:1: 1 

 ratio is 50.5:25.3:25.3. while on the 9:3:4 ratio the ex- 

 pectation is 56.8 : 18.9 : 25.3. It will be seen that the lat- 

 ter figures more nearly fit the observed numbers. 



A 9:3:4 ratio presumes a bifactorial composition. 

 However, a moment's consideration shows that such a 

 ratio cannot have its usual significance in this case. If 

 this were the usual bifactorial segregation, one out of 

 every nine F 2 piebald beans ought to breed true in the 

 third generation. Yet out of 15 rows from piebald beans 

 which certainly belong to the F 3 or F 4 generation not a 

 single one bred true. 



Further, one half of the F 2 Old-Fashioned Yellow Eye 

 segregates and two thirds of the F 2 Improved Yellow Eye 

 segregates ought to show segregation in the third genera- 

 tion. In 1915, 43 Old-Fashioned Yellow Eye, F 3 plants 

 were grown and every one bred true. At the same time 38 

 F 3 plants were grown from Improved Yellow Eye seed. 

 Thirty-seven of these gave typical Improved Yellow Eye 

 beans, but one plant gave piebald beans. The F 2 plant 

 which furnished this latter seed was grown without any 

 protection from insects in 1912 and it is very probable 

 that the one I. Y. E. bean which gave piebald seed was due 

 to insect pollination with Old-Fashioned Yellow Eye 

 pollen. This is all the more probable because the ratio 

 1 : 37 is by no means what would be expected on the usual 

 bifactorial hypothesis. 



The evidence is fairly conclusive that the I. Y. E. and 

 the 0. F. Y. E. segregates breed true and that beans with 



