A rheini(;al inethod of distinguishing genetic types of yellow cones in Rudbeckia. 215 



An experiment with the recessive chocolate rayed character strongly 

 supports this view. Three chocolate plants which wei'o heterozygous 

 for l^lack Yellow gave selfed offspring with a total of 25 purple to 

 9 yellow coned individuals. The 9 yellow plants must have been 

 homozygous for chocolate since this character is a i-ecessive and breeds 

 true. The Black Yellow factor inhibited the expression of chocolate 

 color in the rays of the 9 yellow coned offspring. The 25 purple coned 

 plants were all chocolate as was to have been expected. 



lY. Inheritance of Black Yellow conen. 



The Black Yellows comprise the clones of our original plant (R2.S) 

 and segregates having this plant as one of the ancestors. As shown 

 in Tables 2 and 3, the character, Black Yellow, is inherited as a simple 

 Mendelian recessive. The yellow segregates run somewhat lower than 

 expectation, as is often true of recessives. Some of the aberrant pedigrees 

 with only purple plants can be attributed to selfing in the Pi generation. 

 In other cases such an explanation will not suffice. 



Table 2. Rudbeckia hirta. 

 Inheritance of Black Yellow Cones (R23 and ^ts segregates) 

 a) Black Yellows X Black Yellows and Black Yellows selfed. 



Year 



No. of Pedigrees 



Total P 



Total Y 



BY 



Y, not tested 



1917 



1917 (self s) 

 1919 



37 

 6 



8 



67.5 



177 

 108 



352 



35 



103 



323 

 142 







Totals 46 ■ I | 955 j 490 | 465 



b) Black Yellows X Purples and Reciprocals (F^ generation). 



') The single yellow coned plant from the cross BY X P probably came from • 

 the selfing of the yellow coned parent. 



