vi] MENDELIAN HEREDITY 77 



random give offspring in the ratio of 9 with C and 72, 

 3 with c and ft, 3 with G and r, 1 with c and r. But 

 only those containing both C and R can produce colour 

 and therefore 9 coloured appear to 7 white. Further, 

 among the coloured individuals of F 2 , both purple 

 and red appear, because the factors C and R together 

 produce only red ; to get purple a third factor for 

 blue (E) must also be present, which can only take 

 effect in the presence of both C and R. Since B 

 was introduced by one only of the original whites, 

 the F l purples were heterozygous for blue as well 

 as for C and R (with fully represented constitution 

 CcRrBV) and hence among the F 2 plants one quarter 

 contain no B and in the presence of C and R are 

 red 1 . 



1 In this account, the production of colour (red) is described as 

 being due to two factors (C and R). The recent work of Miss 

 Wheldale [42] on the chemical nature of flower-colours indicates 

 that the essential bodies are an organic base or * chromogen ' and 

 an oxidising ferment. The work of Chodat and Bach, however, 

 indicates that such oxidising ferments must contain two components, 

 neither of which alone is able to oxidise the chromogen and produce 

 the coloured derivative anthocyanin. Both kinds of white sweet- 

 pea contain the chromogen, but it seems probable that one component 

 of the oxidising ferment is present only in one, and the other com- 

 ponent only in the other. Hence no colour can be produced in either. 

 But on mating the two whites together, the mechanism for the 

 oxidation of the chromogen is again complete, and red colour 

 (anthocyanin) is formed. The purple colour (represented by the 

 additional * factor ' B) is due to a further stage of the oxidation 

 of the chromogen than when only red is produced. In some white 



