ANTHOCYANINS 339 



In view of these facts Overton considered that anthocyanin 

 had some connection with tannins, and was probably a gluco- 

 side. A similar view was held by Combes,* who called atten- 

 tion 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 f also indicate the relationship 

 between anthocyanin and sugar. He found that in the leaves 

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

 severed, anthocyanin made its appearance in the mesophyll 

 supplied by these veins. Boodle then experimented with 

 species of Oenothera ; all the species examined were not 

 equally responsive, but in the case of 0. 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 carbo- 

 hydrates which leads to the development of anthocyanin. In 

 this connection the work of Linsbauer J may be consulted. 

 Keener,§ from his observations on Diervilla lonicera, con- 

 cludes that the chief factors which affect the formation of 

 anthocyanin are the degree of insolation, the rate of tran- 

 spiration, the water content of the soil, and the composition 

 of the soil. 



That the presence of anthocyanin is connected with nutritive 



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

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

 X Linsbauer : " Oestr. Bot. Zeit.," 1901, 5i» i- 

 § Keener : " Amer. J. Bot.," 1924, li, 61. 



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