oo6 SCIENCE PROGRESS 



A somewhat similar scheme was put forward by him for the 

 hollyhock pigments. 



During the years covered by this series of papers by Grafe, 

 a considerable amount of work had been published by botanists, 

 dealing with the formation of the anthocyans in plants. Miss 

 Wheldale, as the result of much botanical work, came to the 

 conclusion that the anthocyans are derived from colourless or 

 faintly coloured chromogens (probably flavone or xanthone 

 derivatives) by oxidation, most probably as the result of the 

 action of peroxidases. She considered that the chromogens 

 were produced by hydrolysis of glucosides that existed in the 

 plant, this reaction being reversible. An essential feature of her 

 theory is that the oxidation of the chromogen, with production 

 of anthocyan, can only take place after the hydrolysis of the 

 glucoside. To represent these changes she proposed the follow- 

 ing scheme : 



Glucoside •+- H 2 ^ Chromogen -+- sugar, 

 then : Oxidation of chromogen 1 —> Anthocyan pigment. 



As chemical evidence of the latter part of these changes, Nieren- 

 stein and Wheldale (Ber. 191 1, 44, 3487) and Nierenstein (Ber. 

 191 2, 45, 499) brought forward products obtained by the oxida- 

 tion of quercetin and chrysin respectively with chromic acid, and 

 which they described as " anthocyan-like " products. The re- 

 actions from which they drew this conclusion are, however, by 

 no means sufficient to show that any relationship exists between 

 these compounds and the anthocyans. In this connection, it is 

 necessary to mention the observation of A. G. Perkin (Journ. 

 Chem. Soc. 191 3, 650), that gossypetin by oxidation in alkaline 

 solution yielded a substance (gossypeton) which was deep blue 

 in alkaline solution, but became red on acidification, accompanied, 

 if in concentrated solution, by the precipitation of the red pig- 

 ment. He pointed out the bearing of this observation upon the 

 theory of Miss Wheldale. The fact, however, that this pigment 

 is stable to alkalies is not in agreement with the properties of 

 such anthocyans as have as yet been investigated. 



Keeble, Armstrong, and Jones (Proc. Roy. Soc. B. 1912,85, 215, 

 B. 1913, 86, 308 and 318, B. 1913, 87, 113, and Keeble and Arm- 

 strong, Journ. Genetics, 1913, 2, 277) have published a number of 



1 This oxidation may, or may not, be accompanied by polymerisation. 



