TYPES OF FACTOR INTERACTIONS 



167 



illustrated by the cross white glabrous (ccRRVVHH) X cream glabrous 

 (CCrrVVHH). This gives in F l violet hairy plants (CcRrVVHH) which 

 segregate in FZ according to the analysis given in the accompanying 

 checkerboard (Fig. 77). The proportions are 9 violet hairy: 3 cream 

 glabrous: 4 white glabrous. 



The peculiar feature of these relations is the fact that the factor H 

 for hairiness can only act in the presence of C and R. In fact as far as 

 the above experiment goes, the hairy condition might be considered as 

 merely an extra effect of the interaction of C and R. However, glabrous 

 violet plants are known and in these the factor h for the glabrous con- 

 dition must be present. When a violet glabrous (CCRRVVhh) plant 

 is crossed with white glabrous (ccRRWHH] the FI again is violet hairy 

 (CcRRVVHh), this time because the factor for hairiness is brought 

 in by the white plant, and in F 2 the segregation is as indicated in the 



CRVH 



CRVh 



cRVH 



cRVh 



CRVH 



CRVh 



cRVH 



cRVh 



FIG. 78. Ft checkerboard analysis of a cross between violet glabrous (CCRRVVhh) and 

 white glabrous (ccRRVVHH) stocks. 



checkerboard in Fig. 78. The phenotypic ratio obtained this time is 

 9 violet hairy : 3 violet glabrous : 4 white glabrous. 



This analysis not only adequately accounts for the phenomena as 

 given above, but it also accounts for the F 3 results and the various types 

 of results that are obtained by mating other genotypes. In addition 

 Miss Saunders found that when purple or white incana were mated to 

 cream of the type above, the entire series of forms recorded for the 

 previous white X cream mating were obtained and in addition cream 

 hairy and cream glabrous. This at first sight appears to contradict 

 the hypothesis that no cream or white hairy forms are possible. But 

 closer examination has revealed the fact that white incana, which is 

 itself hairy is in reality a colored form, i.e., possesses the factors C and 

 R. This is shown by the fact that a slight tinge develops in flowers of 

 this variety on fading, and in the F 2 from a cross of this form with cream 



