246 PIGMENTS 



In view of these facts, Overton considers that anthocyan 

 has some connexion with tannins, and is probably a gkicoside. 

 A similar view is held by Combes,* who calls attention to the 

 facts that, as compared with the green leaves, the red autumnal 

 leaves o'i Ampelopsis hederacea, etc., contain more sugars and 

 glycosides, the amount of anthocyan varying directly as the 

 sugars and glucosides ; that the dextrins diminish as the 

 sugars and glucosides increase ; and that the formation of 

 anthocyan is not apparently dependent on the insoluble carbo- 

 hydrates. For these and other reasons he concludes that the 

 substance in question is probably a cyclic glucoside which 

 arises, not at the expense of pre-existent sugars and gluco- 

 sides nor of chromogens, but in the ordinary course of con- 

 structive metabolism ; also, he concludes, it is only formed 

 provided that oxygen be present. 



The observations of Boodle f also indicate the relationship 

 between anthocyan and sugar. He found that in the leaves 

 of Rheum, some of the veins of which had been accidentally 

 severed, anthocyan made its appearance in the mesophyll sup- 

 plied by these veins. Boodle then experimented with species 

 of Oenothera; all the species examined were not equally 

 responsive, but in the case of O. biennis the severance of the 

 midrib at about its middle caused the whole region distal to 

 the cut to become red provided the plant were exposed to 

 daylight. The operation interrupted the path of transport of 

 carbohydrate from the leaf, so that sugar accumulated above 

 the cut, and it is this concentration of soluble carbohydrates 

 which leads to the development of anthocyan. In this con- 

 nexion the work of LinsbaueriJ: may be referred to. 



That the presence of anthocyan is connected with nutritive 

 processes there can be no doubt, but other substances besides 

 sugar may come into play ; thus Dendy observed that the ad- 

 dition of protein to the water, caused green plants of Hcona- 

 tococcus to turn red. 



Finally, the work of Wheldale § on colour inheritance in 

 flowers, points to the conclusion that anthocyan is a product of 



* Combes: " .\nn. Sci. Nat. Bot.," 1909, 9, 274. 

 t Boodle: " New Phytologist," 1903, 2, 207. 

 J Linsbauer : " Oestr. Bot. Zeit.," 1901, 51, i. 



§ Wheldale: " Proc. Cainb. Phil. Soc," igog, 15, 137; " Journ. Genet.," 

 1911, I, 10. 



