F. Keeble and E. F. Armstrong 285 



lacks a factor for colour, give rise when crossed with one another to 

 white-flowered offspring only. 



The simultaneous study of the genetical behaviour of P. sinensis and 

 of the distribution of oxydases in the tissues of the plant provides an 

 explanation of this behaviour. For the latter line of inquiry demon- 

 strates that all varieties of P. sinensis, including the pure green-stemmed 

 varieties, contain oxydase in certain of their tissues. Whence it follows 

 that at least enough oxydase for a definite amount of pigment pro- 

 duction is a possession common to all Chinese primroses. We have in 

 this fact the explanation of the failure of green- stemmed varieties to 

 yield a red-stemmed Fi when crossed with one another. It is also clear 

 why the cross, green-stemmed variety by reddish-stemmed variety, 

 yields a reddish-stemmed Fi generation. Thus if we represent the 

 chromogen producing factor by C, its absence by c, and the oxydase 

 producing factor by O, and its absence by o, then green stem x reddish 

 stem 



= Oc X OC, 

 and Fi = OOCc, 



and since both chromogen and oxydase are present in Fi the plants of 

 that generation are pigmented. 



Fi plants of this kind produce gametes OC and Oc, and hence when 

 such plants are self-fertilised the P, generation is of the typical mono- 

 hybrid kind and consists of 30C : lOc, i.e. 3 reddish-stemmed plants: 1 

 green-stemmed plant. 



As we shall show immediately there is a similar agreement between 

 the results of genetical inquiry and those obtained from the study of 

 oxydase distribution in the case of red-stemmed varieties. 



But the broad features of the relation between oxydase and pigment 

 may be seen in an equally striking manner when they are viewed from 

 another standpoint. 



If, instead of fixing our attention on one variety only, we consider 

 the distribution of pigment and oxydase in the different coloured 

 varieties we obtain clear evidence of the truth of the hypothesis that 

 oxydases play a part in pigment formation. For when we adopt this 

 procedure we discover that, as we pass stage by stage from the less 

 pigmented to the more pigmented forms, the new additions of pigment 

 occur in those tissues which in unpigmented and pigmented forms alike 

 are most generally rich in oxydase. In other words, the cells which in 

 general contain most oxydase are prepotentially pigment forming cells. 

 Thus, although in pure green-stemmed varieties neither the ordinary 



Jonm. of Gen. ii * 20 



