ANTHOCYANINS 35 1 



and thus explains it : by the action of an enzyme the antho- 

 cyanin is converted into anthocyanidin and a sugar. The 

 anthocyanidin is then converted into a colourless pseudobase 

 which may be oxidized to a yellow pigment. In the process, 

 light is of importance ; the pseudobase is due to the photo- 

 chemical reduction of the oxidation product of the original 

 pigment. In the dark, on the other hand, anthocyanidin is 

 oxidized, a process accelerated by heat. Noack * also con- 

 cludes that the equilibrium between flavonols and their re- 

 duction products, the anthocyanins, normally is on the side 

 of flavonol. If assimilation is inhibited or depressed, antho- 

 cyanin is formed. Noack's conclusions based on his obser- 

 vations on Polygonum compactiim and other plants is criticized 

 by Combes f who suggests that the anthocyanidin pseudo- 

 bases were probably phlobatannins, and the red substances 

 which Noack obtained by the action of acids were probably 

 phlobaphenes and not anthocyanidins. 



CONNECTION BETWEEN ANTHOCYANINS AND 

 ANTHOXANTHINS. 



A comparison of the formula of cyanidin chloride on page 

 348 with that of quercetin reveals a close relationship between 

 these two substances, and consequently between the fiavones 

 or anthoxanthins and the anthocyanins. Theoretically it 

 should be possible to pass from anthoxanthins to antho- 

 cyanins by reduction, or conversely from anthocyanins to 

 anthoxanthins by oxidation. In the plant no doubt this is 

 effected readily enough by enzymes, but in the laboratory it 

 is more difficult, and so far the only transformation effected 

 has been the reduction of quercetin to cyanidin. J 



The view first put forward by Wheldale § was that the 

 fiavones and flavonols were the precursors of the antho 

 cyanins ; according to her the conversion of flavonols into 

 anthocyanins was due to oxidation. Evidence in support of 



* Noack : " Zeit. Bot.," 1922, 14, i. 



•f Combes : " Compt. rend.," 1922, 174, 58, 240. 



X Willstatter and Mallison : " Sitzungsber. K. Akad. Wiss. Berlin," 

 1914, 769. 



§ Wheldale : " Proc. Camb. Phil. Soc," 1909, 15, 137 ; " Joum. 

 Genet.," 1911, I, 10. 



