A chemical method 



of distinguishing genetic types of yellow 



cones in Rudbeckia. 



By Albert F. Blakeslee, Station for Experimental Evolution, 

 Cold Spring Harbor, N. Y. 



(Eingegangen 15. Oktober 1920.) 



Seite 



I. Introduction 211 



II. Origin of Yellow Coned Races 212 



III. Chemical Tests 213 



IV. Inheritance of Black Yellows 215 



V. Inheritance of Red Yellows . . . ■ 216 



VI. Crosses between Black Yellows and Red Yellows 216 



VII. Discussion ...... 220 



VIII. Summary • . 221 



I. lutroductiou. 



Rudbeckia hirta, familiarly known as the Yellow Daisy or 

 Black Eyed Susan from its yellow rays and purple cone, is a composite 

 often found growing in enormous numbers in neglected meadows. The 

 species is highly variable in the field, the individuals differing widely 

 in size, form and color of the floral parts. 



The central cone or disk, which contains the disk flowers, varies 

 from almost black through various shades of reddish purple to bright 

 red. In our records we have recognized the gi-ades h, f, d and b to 

 indicate progressive reductions in the amount of purple pigment. Absence 

 of purple in the cone, represented by grade „o", is an extremely rare 

 condition. The resulting color is a greenish yellow, shown in figure I 

 in contrast to normal purple cones of about grade f. The breeding 

 work summarized in the present paper indicates that there are two 

 genetic types of yellow cones, each lacking a factor necessary for the 



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