May, 1920.] YASVI.'—GENETICAL STUDIES. 63 



1918. The white double, used in this experiment was raised from 

 the seeds of 1917. If this white double were a homozygote with 

 respect to the whiteness, then the Fi plant should be of only one kind 

 in colour ; while we got in Fi here both the magenta and the 

 yellow. So the white double should be taken for a heterozygo_te 

 with respect to a certain id relating the colour. 



We have reason to say that there were any inhibitorv- factor 

 present neither in the single white ccRRdd, nor in the magenta double, 

 the parents of the white double. But it is clear that this plant is 

 homozygous in lacking C as it has no yellow pigment and will be 

 denoted by cc ; thus it is the natural consequence that it should be 

 heterozygous with respect to R. Thus we put the idic formula 

 ccRrDd for the double white in question, and for the gamates cRD, 

 cRd, crD, crd, thus cRD : cRd : crD : crd xCrd = l CcRrDd (magenta 

 double) : 1 CcRrdd (magenta single) : 1 CcrrDd (yellow double) : 1 

 Ccrrdd (yellow single). 



In this place I should mention that Ikeno's statement (1918) 

 in his book " Zikken-Idengaku " (Japanese) 3. ed., " in a certain race 

 [Portulaca grandiflora] the reddish violet [magenta ?] appears among 

 the offsprings from the crosses between the white and the yellow 

 (orange) , seems certainly to have something in common with the 

 results of the present experiments. 



The yellow character of the petal has been hitherto assumed 

 due to the presence of the flavone derivation and the corresponding 

 id R. But it is equally possible or even more likely that the yellow 

 petal is due to the simultaneous presence of the ids C and R, and 

 the absence of an id which serves the agency to bring them into 

 cooperation. But as we are at present not completely aware of the 

 nature of all of the pigments in Portulaca grandiflora, we are not 

 in the position to decide the point. 



SUMMARY 



1. The character doubleness in the Portulaca grandiflora (at 

 least in the races used in the present experiments), behaves dominant 

 to the character singleness. The number of alleromorphic ids con- 

 cerned appears to be one ; if it is two or more, then they are 

 situated in one and the same chromosome. 



2. The pale yellow colour of the petal is due to the presence 

 of a pigment (may be one of the flavone derivations), which serves 



