Heredity Studies in the Morning-Glory ii 



are in man}?- cases interdependent. Thus, for instance, red anthocyan 

 may be regarded as a highly oxidized and colored product of an oxidase 

 acting upon a colorless chromogen; this oxidase, therefore, is equivalent 

 to the "reddening factor" of the mendelists. Similarly, a second oxidase, 

 the mendelian "bluing factor," leads to the formation of purple antho- 

 cyan from the product of the action of the reddening oxidase (red antho- 

 cyan). But the bluing oxidase is unable to form pigment directly without 

 the process of the reddening oxidase. If the power to form the bluing 

 oxidase is lost from the purple type, a red variety is the result; if the 

 reddening factor is lost, an albino results, which may still contain the 

 ferment capacity for the bluing action. 



In this way can be represented, in terms of mendelian genes and in terms 

 of oxidases, the series of genetically different varieties which actually 

 exist, ranging as they do in such plants as stocks and morning-glories 

 from pink thru mauves, magentas, and reds, or thru the blue series to 

 the purple type. It is evident that the loss of either element, peroxide 

 or peroxidase, will give rise to albinism, even tho the plant may still carry 

 the bluing factor or other modifying genes. Hence in any species having 

 a complex series of color varieties there are a number of possible albinos, 

 both genotypically and physiologically different from one another. The 

 colors of varieties arising from an anthocyanic type may be regarded as 

 components of the original anthocyan of the wild ancestral prototype. 

 Conversely, the type may be supposed to have lost its components in 

 succession, thus giving rise to a series of color variations. 



This chromogen-oxidase theory of the formation of anthocyanic colors 

 furnishes an explanation for the behavior of the color types of the morning- 

 glories here studied. Their genetical behavior is considered in the next 

 section, where it is shown that these color types form an epistatic series, 

 each step of which is determined by the active presence of a particular 

 gene or complex of genes which are probably in the nature of en7ymes. 



THE GENETICS OF COLOR TYPES 



In accord with the enzyme-chromogen hypothesis of the formation of 

 floral pigments, the following sjonbols and formulas are here used as 

 working hypotheses to account for the genetic relationships of the various 

 color types of morning-glories used in the present study: 



Symbols 

 C= Chromogen 

 R = Oxidase acting on C 

 B = Bluing gene 



X == Peroxidase or intensifier acting on C and R, and on B 

 I ^A further intensifying gene 



127 



