220 Blakeslee. 



Another possibility that cannot be exchided without further breeding 

 experiments is that the double recessive, homozygous for both RY and 

 BY, fails to appear in F^. If this be true, the purples and yellows 

 should form a 9:6 ratio and the two types of yellows a 1 : 1 ratio. 

 The deviation of our purples and yellows from a 9:6 ratio is about 

 equal to the probable error and the deviation of the two t^^pes of yellows 

 from a 1 : 1 ratio is 1"4 times the probable error. Our figures therefore 

 agree well with the assumption of the double recessive failing to appear 

 in the F2. Since experimental evidence is lacking other than that offered 

 by the ratios obtained, it seems best to leave the assumption represented 

 in figure 1 as a tentative representation of the type of segregation in 

 the F2 generation. • 



Til. DisciissioD. 



The two yellow cone types offer an example of complementary 

 factors, to use the terminology of the presence and absence hypothesis. 

 The presence of such complementary pairs of factors has been found 

 not to be a rare phenomenon since Bateson and his associates') first 

 demonstrated the existence of two kinds of white Sweet Peas which 

 when crossed throw purples. 



The chief interest in the present example from Rudbeckia lies in 

 the sharp chemical differentation possible between genetic types which 

 are similar phenotypically. Wheldale^) reports that the whites extracted 

 from different colored varieties of Mathiola and Lathyrus, though all 

 giving the oxydase reactions, did not give the reaction to the same 

 extent, that is, it varied in intensity. So far as the writer is aware, no 

 other case has been reported than the one in the present paper where 

 a sharp chemical distinction could be established between the genetic 

 groups within a phenot3q)e. It is believed, however, that should thorough 

 tests be made with other material, as strikiug results could be obtained 

 as with the cone colors of Rudbeckia. The advantage to the geneticist 

 of being able to analyse his material without recourse to actual breeding 

 operations is obvious and need not be dwelt upon. 



^) Bateson, W., Saunders, E. R. and Punnett, R. C, 1904. Experimental 

 Studies in the Physiology of Heredity. Rep. Evol. Com. Roy. Soc. Rpt. II. 



*) Wheldale, M. The Anthocyanin Pigments of Plants. I9I6. Univ. Press, 

 Cambridge, Eng. Pg. 212. 



