The Factor Hypothesis 65 



insure the production of the purple color. As a matter 

 of fact, just this result has been actually realized in 

 practically all such crosses. In one case, however, 

 startlingly different results were obtained. Crossing 

 just such a purple parent as was mentioned with a white- 

 grained race resulted in an Fi generation which was all 

 white. 



Inbreeding this Fi gave an F2 generation which con- 

 tained some colored grains, but a decided majority of 

 whites. Evidently the colorless condition is dominating 

 over the colored. This would be surj^rising in any case 

 of color inheritance, for we always expect colored to be 

 due to the presence of something that is absent in col- 

 orless. 



Analysis of the present case revealed the fact that 

 the white-grained race that had been used was homozy- 

 gous for the presence of an inhibitory factor, /; whenever 

 this factor is present no color of any kind can be produced. 

 This readily explains the foregoing results. If the purple- 

 grained race that was used had the fonnula iiPPRRCC 

 and the white-grained race was IIPPRRCC, the result- 

 ing Fi would be IiPPRRCC, which would be pheno- 

 t}^pically white owing to the presence of the / factor. 

 Inbreeding would then result in the following F2: i 

 IIPPRRCC, phenot>TDically white; 2 IiPPRRCC, white; 

 I iiPPRRCC, purple. It is clear that the colorless con- 

 dition is actually dominating, but it is dominating on 

 account of the presence of the / factor. 



It is evident that the purple and red types with which 

 we had been dealing before must all have been homozy- 

 gous for the absence of /. Corn grains can be colorless 

 for any of three reasons, absence of R, absence of C, or 



