90 



MENDELISM chap. 



actually consists of only three forms, viz. erect red, 

 erect purple, and hooded purple, and the ratio in which 

 these three forms occur is i : 2 : i. No hooded red has 

 been known to occur in such a family. Moreover 

 further breeding shows that while the erect reds and 

 the hooded purples always breed true, the erect purples 



Painted Lady X Duke of Westminster 



{erect redj 



(hooded purple) 



Purple Invincible 

 (erect purple) 



I \ I 



Painted Purple Invincible Duke of 



Lady ~ Westminster 



(I) (2) (^) 



in such famihes never breed true, but always behave 

 like the original Fi plant, giving the three forms again 

 in the ratio 1:2:1. Yet we know that there is no diffi- 

 culty 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 be- 

 tween the factors for erect standard and blue in a plant 

 which is heterozygous for both, thispeculiar case receives 

 a simple explanation. The constitutions of the erect 

 red and the hooded purple are EEbb and eeBB respectively 

 and that of the Fi erect purple is EeBb. Now let us 

 suppose that in such a zygote there exists a repulsion 



