THE OXIDASES IN RELATION TO PIGMENTATION 279 



certain colour changes with acids, alkalies, hydrogen per- 

 oxide and nascent hydrogen, in becoming decolorized in 

 neutral solutions of alcohol (owing to isomerization), and in 

 being restored in colour by acids. The absorption bands 

 given by the natural anthocyanin and by Everest's com- 

 pounds were also found to be similar. However, Wheldale 

 and Basse tt (1914, 3), are of the opinion that such reduc- 

 tion products are of quite different structure from the 

 natural anthocyanins. The writer does not feel competent 

 to decide between the conflicting results, but he is of 

 opinion, after a survey of their evidence, that neither 

 Combes nor Everest have definitely established the identity 

 of their products with natural anthocyanin. 



Wheldale and Bassett have also obtained a coloured 

 substance by the reduction of quercetin. Analyses of this 

 showed it to be a reduced derivative of quercetin, from 

 which its molecular weight differed but little when deter- 

 mined by the raising of the boiling-point of alcohol. It 

 does not, however, in their opinion resemble any natural 

 anthocyanin. 



FACTORS INFLUENCING THE PRODUCTION OF 

 ANTHOCYAN PIGMENTS. 



From the time of Senebier (1791), numerous physiologists 

 have studied the anthocyan pigments and the influence of 

 various factors upon their production. Evidence as to the 

 effect of exposure to light and to high and low tempera- 

 tures was slowly accumulated, and the researches of Over- 

 ton (1899) appeared to prove that in certain plants ex- 

 posure to light was necessary for the production of antho- 

 cyanin. Working with Hydrocharis morsus -ranee, he 

 further showed that, other conditions being maintained 

 constant, low temperatures favoured the production of 



