A chemical method of distinguishing genetic types of yellow cones in Rudbeckia. 221 



VIII. Summary. 



1. Ill the Black Eyed Susan (Rudbeckia hirta), which typically 

 has purple cones, two genetic races have been found with yellow cones. 



2. In both races the factor for presence of yellow cones inhibits 

 the production of red pigment throughout the plant. 



3. These races are indistinguishable in appearance but show 

 different color changes when their cones are treated with various 

 chemicals. 



4. The cones of one race turn black in KOH and NaOH and this 

 race is called Black Yellow; the other race has its cones turn red in 

 KOH and is called Red YeUow. 



5. The Black Yellow character and the Red Yellow character are 

 individually inherited as simple Mendelian recessives. 



6. When Black Yellows are crossed with Red Yellows the Fi 

 generation consists of purple coned individuals. 



7. In the Fg generation purples and yellows form a 9 : 7 ratio. 



8. By means of KOH the two yellow t}"pes can be distinguished 

 and a 9:4:3 ratio established as illustrated in the colored diagram. 



9. It is concluded that the genes for Black Yellow and Red Yellow 

 are located in different chromosomes. 



10. The desirability of attempting by means of chemical reagents 

 to resolve phenotypes into genetic groups in other forms is suggested. 



Plate 9. 



Colored diagram to illustrate segregation in Fj generation from a cross between Black 



Yellow Cones and Red Yellow Cones in Rudbeckia hirta. Cones in parentheses show 



colors of adjacent cones after treatment with KOH. 



