No. 518] COLOR INHERITANCE 87 



the other. In order to produce a second stage of color it 

 is necessary to assume the occurrence of a third gene 

 which can make its characteristic color-reaction apparent 

 only in the presence of the other two. Thus in Lathyrus, 

 etc., it was assumed that two factors, R and C, are neces- 

 sary to the production of a red anthocyan color, and that a 

 third factor, B, modifies this color to bluish. This as- 

 sumption requires that the presence of each of these three 

 genes be dominant over its absence. An alternative as- 

 sumption might have been made, viz., that the absence of 

 the third factor is dominant over its presence. Then the 

 lowest grade of color would be a blue color produced by 

 the simultaneous presence of B and C, and the red color 

 would appear only when R is present in the homozygous 

 state. 



Last year in my discussion of the presence and ab- 

 sence hypothesis (Shull, 1909) it was pointed out that it 

 would be impossible in many cases to determine "whether 

 red flowers are blue flowers with an added factor for 

 acidity or whether blue flowers are red with an added 

 factor for alkalinity, ' ' and also that "it is conceivable 

 that both these situations may be presented in different 

 species. " The color characters in Lychnis give a very 

 good illustration of these statements. 



If we assume the dominance of presence over absence, 

 the lowest grade of color the bluish is formed by the 

 combined action of two genes, B and C, the one probably 

 representing, according to the studies of Miss Wheldale 

 (1909), the capacity to produce a chromogen of the 

 flavone series, the other representing the production of 

 an oxidase. The red color is in this case produced by an 

 added factor, R, which modifies the bluish color produced 

 by B and C. The R may be perhaps an acidifier, a re- 

 ducing agent, or a partial inhibitor of the oxidizing 

 action of B. This method of explaining color inheritance 

 in Lychnis presents an interesting reversal of the places 

 occupied by R and B when compared with the situation 

 in other plants. 



