IX REPULSION AND COUPLING 83 



has been known to occur in such a family. More- 

 over, further breeding shows that while the erect 

 reds and the hooded purples always breed true, the 

 erect purples in such families never breed true, but 



Painted Lady X Duke of Westminster 



(erect red) 



(hooded purple) 



Purple Invincible 

 (erect purple) 



I 1 1 



Painted Purple Invincible Duke of 



Lady Westminster 



(I) (2) (I) 



always behave like the original F^ plant, giving the 

 three forms again in the ratio i : 2 : i. Yet we 

 know that there is no difficulty in getting purple 

 bicolors to breed true from other families ; and we 

 know also that hooded red sweet-peas exist in other 

 strains. 



On the assumption that there exists a repulsion 

 between the factors for erect standard and blue in 

 a plant which is heterozygous for both, this peculiar 

 case receives a simple explanation. The constitutions 

 of the erect red and the hooded purple are EEbb 

 and eeBB respectively, and that of the F^ erect 

 purple is EeBb. Now let us suppose that in such a 

 zygote there exists a repulsion 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 the zygotic series EEbb -|- 2 EeBb ■\- eeBB, i.e. 



