ix REPULSION AND COUPLING 91 



between E and B, such that when the plant forms gametes 

 these two factors will not go into the same gamete. 

 On this view it can only form two kinds of gametes, viz. 

 Eb and eB, and these, of course, will be formed in equal 

 numbers. Such a plant on self-fertilisation must give 



EEbb eeBB Parents 



- 

 %\eB 



0+ 



EEbb 



^ — Eb 



EeBb 



^—eB 



EeBb 



^—Eb 



eeBB 



^—eB 



F 8 generation 



the zygotic series EEbb 4- 2 EeBb 4- eeBB, i.e. 1 erect red, 

 2 erect purples, and 1 hooded purple. And because the 

 erect reds and the hooded purples are respectively homo- 

 zygous for E and B, they must thenceforward breed true. 

 The erect purples, on the other hand, being always formed 

 by the union of a gamete Eb with a gamete eB, are 

 always heterozygous for both of these factors. They 

 can, consequently, never breed true, but must always 

 give erect reds, erect purples, and hooded purples in the 

 ratio 1:2:1. The experimental facts are readily ex- 

 plained on the assumption of repulsion between the two 



