1^0. 643] SEROLOGICAL PHENOMENA 



121 



ular condition that at present exists in the group. Some 

 of them may have been small and sequentially related, 

 and it is not impossible that the extremes were thrown 

 in one line, while grades of less advanced type came into 

 expression in collateral lines. It is also clear that even 

 should certain grades have arisen as a progressive series 

 there is no reason, from the viewpoint of the mutation 

 theory, why any two particular grades should not show 

 the characteristics of Mendelian unit-characters, irrespec- 

 tive of the order of their origin. The important point is 

 that in this group when mutations occur in certain col- 

 or pattern-controlling factors, whether great or small, 

 they tend toward the formation of eye-spots in some 

 degree. 



While we know little of the chemistry of animal pig- 

 ments, the reactions involved in color-production in cer- 

 tain plants are better understood, since many of the pig- 

 ments have been extracted and analyzed. Along with the 

 understanding of structure that has been gained in the 

 chemical studies of synthetic dye-stuffs, has come con- 

 siderable knowledge of the relation between color and 

 molecular structure. In many cases, for instance, as 

 Nietzki- has shown, where the pigments of most simple 

 construction are yellow, by increase of molecular weight 

 they change to red, next to violet, then to blue. A good 

 review of the theories of color in organic compounds, 

 given as an introduction to her own painstaking and 

 valuable chemical researches^ on Pigments of Flower- 

 ing Plants," will be found in a recent paper by Dr. Nellie 

 A. Wakeman. Most of the information about organic 

 pigments used in the present discussion has been obtained 

 from this source. 



Upon reading such a piece of investigation together 

 with the accompanying discussion of related studies one 

 is impressed by the fact that a comparatively few proc- 

 esses underlie most pigmentary changes in plants. En- 

 zymes— hydrolases, reductases and oxidases— frequently 



2 Tra7is. Wis. Acad., XIX, Part II, pp. 767-906, Madison, Wis. 



