76 I. XAGAi : 



separable at the time of synapsis. The character which is due to the end 

 product of the final change, therefore woidd appaar as due also to a single 

 genetic entity. Suppasiug that the purple authoeyanin is produced by C-*B-*P 

 changes and three separate genes are actually taking pai't to biing about 

 complex chemical changes. But if these genes are linked, or so to say, form 

 a complex, and do not separate in gametogenesis, they may weU be considered 

 as a single entity and can be substituted by a single designation to express 

 the genetic entities to a given character. When they separate fi-om the complex 

 by any cause, a supposed single imit character M"ould appear to be constituted 

 by more than a single gene. 



The separation of genes from tha complex may take place either by 

 hybridization or by unknown internal causes, and of the latter cases, we call 

 mutation. 



It is a comparatively simple matter to determine the number of genes 

 concerned with given characters by h^'bridization experiments when the 

 contrasting characters are distinct and the segregation in the oflfepring of the 

 hybrid is sharply defined. But it is exti-emely difficult to interpret those 

 genes in terms of biochemisti-y or physiology. We are likely to fall into the 

 danger of providing a superficial analogy and di'awing sweeping CDnclusion by 

 confusion of the geuetical data to those of physiology. 



lu the case of the formation of anthocyanin and phlobaphene pigments 

 in the plants studied, the genes C, 0, R and P appear to govern certain 

 gi'oups of biochemical reactions in the sporophytic cells more or less in a 

 distinct manner, yet we must have great reserve in referring these genes to 

 any physiological factors. It is time that the paroxidase coexists with the 

 pigment, and the normal oxygen relation is essential to the formation of the 

 pigment, but these facts prove in no way to jillow us in intei-preting the 

 complementary gene of the colour producing system in plant is exclusively 

 relating to peroxidase. Even in the case of the formation of brown and 

 reddish brown pigments, in which the oxidation of the chromogenic substance 

 is an essential change, the direct inference of the geue to peroxidase or 

 oxidase may deserve serious consideration. 



The formation of brown plant-pigments (plili)baphenes) resembles, as we 

 have ah-eady seen in the precethug pages, that of melanin pigments in animals 



