ANTHOCYANINS 249 



pound has a red tint. When treated with alkali, blue metallic 

 salts are formed, while the arrangement shown in the formula 

 II. represents a neutral compound having a violet tint. The 

 neutral violet tinted delphinin has been isolated from Del- 

 phinium consolida by Willstatter and Mieg,* and has been 

 shown to turn blue with alkali, and red with acids ; the 

 colour would therefore appear to act as an indicator in the 

 plant itself, showing whether the cell sap is neutral acid or 

 alkaline. 



The colours of different flowers are not necessarily due 

 to the same anthocyanin. Willstatter found three pigments 

 in the cornflower : purple, an acid flavone derivative ; blue, 

 the potassium salt of the purple ; and red, an oxonium type 

 of salt of anthocyanin with an acid present in the cell sap. 

 Wheldale and Bassett,f on the other hand, conclude that the 

 anthocyanins of Antirrhinum must be different from those of 

 Centaurea, since in the latter plant no oxonium salts are pro- 

 duced with mineral acids ; further, the dissimilarity in the range 

 of colour varieties thrown by the plants in question also sug- 

 gest the same conclusion. If, in Antirrhinum, the antho- 

 cyanins are derived from flavones, their origin must in part be 

 due to oxidation since the red and magenta anthocyanins 

 contain a much higher percentage of oxygen than do flavones. 

 The anthocyanin molecule is apparently larger than the 

 flavone, so that if the chromogen is flavone, its condensation 

 must be either the combination of two flavone molecules or 

 one flavone molecule with one or more molecules of phenol, 

 or an aromatic acid, etc. 



Sometimes it is observed that the leaves of certain plants 

 when first they unfold are bright red and that in a few days 

 this colour fades away and the green colour is seen. Noack J 

 has investigated this phenomenon in Polygonum compactum, 

 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, 



* Willstatter and Mieg : " Annalen," 1915, 408, 61. 



t Wheldale and Bassett: " Biochem. Journ.," 1914, 8, 204. 



% Noack: " Zeitsch, Bot,," 1918, 10, 561. 



