No. 551] THE MENDELIAN NOTATION 655 



factors are necessary for the production of the purple 

 color. How many other factors (present also in the 

 whites) may be necessary one can not say. In another 

 white, the R factor is present and purples and whites in 

 the ratio of 9 : 7 result. In another white, both P and R 

 are present. In another white, both P and C are present. 

 Both give monohybrid ratios when crossed with the 

 purple. 



This is not the sum total of whites, however; several 

 others have been found. One has an intensifying factor. 

 We get darker purples together with the normal purples, 

 but no one can doubt that the purple is still the same pig- 

 ment modified in its expression. Another white has a 

 dominant inhibiting factor. In the heterozygous condi- 

 tion it does not always inhibit the color entirely, but in 

 the homozygous condition color never develops. The 

 dominance of this factor is proved by the fact that ex- 

 tracted colored recessives are still heterozygous for pres- 

 ence of color. 



In still other whites I have, demonstrated the presence 

 of at least three modifying genes M^M^M^ They are 

 independent of each other, yet each and all affect the 

 purple color. One is dominant, as if it were a partial 

 inhibitor, the others are recessive, as if they were the loss 

 of intensifying factors. Purples of all different degrees 

 can be isolated and breed true. The lightest is such that 

 the color can be distinguished only with a lens. But they 

 are all strictly alternative in their transmission and 

 somewhere near the expected ratios of darks, lights, very 

 lights, etc., appear. It is too much to ask that exact ra- 

 tios be obtained for with this kind of modification all 

 shades appear, yet conclusive evidence has been ob- 

 tained by F 3 and F 4 generations. 



The qualitative characters do act the same as quanti- 

 tative characters, therefore, and one can not make a real 

 distinction between them. 



