1915] B. Horowitz 171 



occur as glucosides in many plants, the following scheine of reaction 

 was suggested :^® 



( 1 ) Glucoside + water ^ flavone + sugar. 



(2) X (flavone) + oxygen—>anthocyanin. 



In addition to oxidation there might be condensation of the 

 flavone molecules. Reaction (i) may be controlled by a glucose- 

 spHtting enzyme, and (2) may be due to an oxidase. Many authors 

 have shown that oxygen or oxidase plays an important part in an- 

 thocyanin formation.^'^ 



Acid turns anthocyanins red; alkali, blue. This characteristic 

 feature of these pigments naturally suggested that the red modifi- 

 cation behaves Hke a weak acid, and the blue Hke a weak alkali. 

 The fact that an excess of alkali gives a green instead of blue color 

 has been explained by the assumption that anthocyanin is a bi-basic 

 acid. 



Attempts to trace some relationship between anthocyanin and 

 Chlorophyll have not been wanting. Thus, it had been stated that 

 leaves containing anthocyanin have relatively less Chlorophyll than 

 those which do not contain anthocyanin.^^ Macaire's hypothesis 

 that Chlorophyll is transformed into anthocyanin held sway for 

 many years, tili Mohl disproved it. Mulder was of the opinion that 

 the decomposition of Chlorophyll gave rise both to blue and yellow 

 pigments. ^^ None of these Statements has been substantiated. 



A close chemical relationship between anthocyans and flavones 

 has been shown by Willstätter.^*' As has been stated Willstätter 

 has f ound that the anthocyan of corn flower can be hydrolyzed into 

 glucose and cyanidin. Now, if quercetin, a hydroxy-derivative of 

 flavone, is dissolved in alcohol, made strongly acid with hydro- 

 chloric acid, and reduced at 35° with Mg-Hg, a small quantity 

 of cyanidin is formed. The Solution can be concentrated and the 

 separated cyanidin and quercetin filtered off, dissolved in alcohol, 

 and the cyanidin precipitated with ether : 



2« Wheldale: Proc. Roy. Soc. (B), 1914, Ixxxvii, p. 301. 



27 Malvezin : Compt. rend., 1908, cxlvii, p. 348. MoUiard : Ibid., 1909, cxlviii, 

 P- 573- Combes: Ibid., 1910, cl, pp. 1186, 1532. Keeble and Armstrong: Jour. 

 of Genet., 1912, ii, p. 277. See also Czapek, Biochemie der Pflanzen, 1913, i, p. 591. 



28 Haas and Hill : Chem. of plant products, 1913, p. 244. 



29 See Czapek : Biochemie der Pflanzen, 1913, i, p. 586. 



30 Willstätter and Mallison : Sitz, preuss. Akad. Wiss., 1914, xii, p. 769. 



