ANTHOCYANIN AND SUGAR 255 



were important factors. If the temperature be low, but above 

 freezing-point, then the formation of the red pigment will be 

 promoted, which accounts for the red colour prevalent in 

 alpine plants, since under their conditions of existence sugar 

 tends to accumulate rather than starch. This also is true for 

 arctic plants in which, according to the observations of Wulff,* 

 the leaves are very frequently sugar leaves, and are commonly 

 characterized by the presence of anthocyanin. 



In the case of Hydrocharis grown in water culture, Overton 

 found that when the temperature and the intensity of light 

 were so balanced that no colour was formed, the addition of 

 2 per cent of invert sugar caused its appearance in three days, 

 not only in the young leaves but also in the old ones. 



Other aquatic plants behaved similarly, but in the case of 

 cut shoots of lilies the red pigment only developed provided 

 sugar were added to the culture solution. 



Further experiments showed that the red colour is not 

 formed in those plants, in which the pigment was restricted to 

 the epidermis, when cultivated in sugar solution. Success only 

 resulted in those cases where the colouring matter occurred in 

 the mesophyll. 



In view of these facts Overton considered that anthocyanin 

 had some connexion with tannins, and was probably a glucoside 

 (p. 249). A similar view was held by Combes,f who called 

 attention to the facts that, as compared with the green leaves, 

 the red autumnal leaves of Ampelopsis hederacea, etc., contain 

 more sugars and glucosides, the amount of anthocyanin vary- 

 ing directly as the sugars and glucosides ; that the dextrins 

 diminish as the sugars and glucosides increase ; and that the 

 formation of anthocyanin is not apparently dependent on the 

 insoluble carbohydrates. For these and other reasons he con- 

 cluded that the substance in question was probably a cyclic 

 glucoside which arose, not at the expense of pre-existent 

 sugars and glucosides nor of chromogens, but in the ordinary 

 course of constructive metabolism ; also, he concluded, it was 

 only formed provided that oxygen be present. 



The observations of Boodle J also indicate the relationship 



*Wulff: " Botanische Beobachtungen aus Spitzbergen," Lund., 1902. 

 + Combes: "Ann. Sci. Nat. Bot.," 1909, 9, 274. 

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



