THE OXIDASES IN RELATION TO PIGMENTATION 267 



veins of Iris Monnieri. The effect, apparently, is only 

 brought about slowly, for, although it is noticeable after 

 twenty-one hours, it only becomes well marked after sixty- 

 six. It may also be seen that the age of the flower is 

 without influence on the intensity of the reactions, except 

 that in the buds the latter are not as strong as in the more 

 mature flowers. Since these buds opened in the dark, it 

 is clear that the absence of active peroxidase cannot be 

 due to its destruction by light. 



The almost complete absence of peroxidase activity, as 

 judged by the a-naphthol reaction, in certain deep-claret- 

 coloured varieties of /. xiphioides, is hard to reconcile with 

 the view that the pigment is produced as the result of the 

 action of the enzyme. Treatment with hydrogen cyanide 

 or with toluene, as previously described, resulted in the 

 production of the a-naphthol purple in the veins of the 

 falls when the reagent was subsequently added. Thus it 

 appears that in this case the presence of a powerful in- 

 hibitor, which is removed by the above methods, renders 

 the enzyme inert. If the production of inhibitor occurred 

 after pigment formation or in definitely localized portions 

 of the cells, the discrepancy might be explained. It is, 

 however, quite likely that the inhibitor is a reducing agent 

 sufficiently strong to check the oxidation of a-naphthol. 

 The subject is one which leaves much room for further 

 work, and the author hopes to be able to investigate the 

 matter more fully. 



SECTION II. THE ANTHOCYAN PIGMENTS. 



ANTHOCYANINS AND THEIR PARENT SUBSTANCES. 

 The chemical constitution of this group of substances is 

 now fairly completely known through the researches of 

 Willstatter and his pupils, which have shed much light on 



