32 Colour and other Characters in the Potato 



" Flourball " has therefore yielded three types of potato which have 

 been identified by reason of their gametic qualities, namely, two reds, 

 one giving reds to whites in the ratio 9 : 7, another red to white in the 

 ratio 3 : 1, and a white variety. 



In order to elucidate further the colour factors the white variety D 

 was crossed by the 3 : 1 red variety A and the result was 



27 Red to 22 White. 



This ratio is presumably to be taken as approaching equality, as 

 9 : 7 ratio would be here impossible. 



If the formula of A be RrDD then this particular white potato 

 must be rrDD ; similarly if A be RRDd then the white variety must 

 be RRdd. It is here assumed that A = RrDD, and the family D 

 therefore will be represented by rrDD, it could of course be equally 

 well rrDd. 



A cross of peculiar interest was made between " Flourball " and a 

 potato called " Record " which, although of attractive appearance, was 

 of such frail constitution that it has entirely died out everywhere. 

 The result of the cross was a family H. Of the 30 individuals which 

 lived through the following years 19 were white and 11 red. The 

 numbers are small, but enough at least to show that the whites are 

 in a very distinct majority. If the notes of the H family be examined 

 from its first origin, one finds that there were 28 whites to 12 reds and 

 two with no tubers, and that the mortality has taken place amongst the 

 white and tuberless. 



The formula for " Flourball " was shown to be RrDd, and there are 

 two possible formulas for a white potato which would, in union with 

 " Flourball," give rise to a family having a majority of whites. They 

 are rrdd and rrDd respectively ; — the first would give a family of 

 three whites to one red ; the second would give a family of five whites 

 to three reds. The numbers in the H family are not large enough to 

 decide with certainty which formula for " Record " is the more correct. 

 We have seen that the mortality affected those plants which were 

 either white tuber bearers or tuberless, and that the approximation of 

 the final result of two whites and one red is due to this mortality 

 amongst the whites. Whether it is possible that plants pure to the 

 absence of pigment factors are more weakly than others cannot, on the 

 present evidence, be asserted, but the facts suggest such a possibility. 



Two white-tubered members of the H family were crossed by the 

 red potato A, whose gametic composition we may assume to be RrDD, 



