CH. V] 



Reversion in Colour 



89 



sixteen individuals 9 will contain both the dominant or 

 present factors, while of the remaining 7 individuals, 3 will 

 contain the one dominant, 3 will contain the other, and i 

 will contain neither. There will therefore be 9 which are 

 coloured and 7 which are albino. In the diagrammatic 

 scheme C and R are the symbols representing the two 

 complementary factors, c and r being their respective allelo- 

 morphic absences. 



Fig. 16. Composition of the 9 coloured and 7 albino offspring in F^ 

 from the cross between albino Cr with albino cR, showing the ratio 

 9 coloured : 7 albinos. 



Tvv^o examples of this phenomenon have been studied 

 in detail. The first is that provided by the Sweet Pea 

 {Lathyrus odoratus) which has formed the subject of ex- 

 periments carried on jointly by Mr Punnett and myself for 

 some years. 



The work was begun by crossing two white sweet peas 

 belonging to the variety Emily Henderson. These plants 

 were alike in every respect so far as could be perceived, 

 excepting that the shapes of their pollen grains differed, 

 the one having the normal long pollen grains of the species, 

 while the other had roundish grains. The object of the 

 experiment was to trace the descent of the pollen-character 

 and at the beginning no question of colour was entertained. 

 When F^ was grown however it was clear that here was a 



