1/2 Plant Pigments [March, 



Cl 

 I 

 OH O OH O OH 



> 



HOr^/^-<f ~>0H + H2 HO/^/\c-<' >0H + HCl HO^,'^\c-<( >0H 



l^/\/COH ^/\/COH \A/COH 



HO CO HO C HO C 



/\ I 



H OH H 



This is in direct contradiction to Miss Wheldale's findings. 

 Here the change f rom a flavone to an anthocyanin product involves 

 reduction, whereas Miss Wheldale regarded the process as one of 

 oxidation. 



The exact influence of Hght in the formation of anthocyanin 

 pigments has yet to be settled.^^ Ewart^^ has shown that, in aquatic 

 plants at least (such as Elodea canadensis) , the red color does not 

 appear if the plant is grown in diffuse sunlight. Overton^^ names 

 temperature as an additional factor : a low temperature, but one 

 above freezing-point, favors the formation of the pigment. This 

 explains the prevalence of red color in alpine plants. 



That anthocyanin formation is dependent upon the presence of 



sugar is suggested by Overton's interesting experiments.^* He 



found that the pigment formation could be artificially induced by 



immersing the cut leaves of many plants in a 2-3 percent sugar 



Solution. This finding was later confirmed and extended by Combes^^ 



and Rose.^^ The fact that anthocyanins are commonly found with 



tannin-like substances has led Wigand to regard the two as closely 



allied. Anthocyanins give the iron reaction and, like the tannins, 



are precipitated by caffein and antipyrin.^^ 



Biochemical Laboratory of Columbia University, 



College of Physicians and Surgeons, New York. 



31 Fischer: Flora, 1908, xcviii, p. 380. Chartier and Colin: Rev. gen. Botan., 

 1911, xxiii, p. 264. Landel: Compt. rend., 1893, cxvii, p. 314. 



32Ewart: Ann. Bot., 1897, xi, p. 461. 



33 O verton : Nature, 1899, lix, p. 296. 



3* Overton : Jahr. wiss. Botan., 1899, xxxiii, p. 171. 



35 Combes : Compt. rend., 1909, clxviii, p. 790. 



3« Rose : Ibid., 1913, clviii, p. 955. 



37 See Czapek : Biochemie der Pflanzen, 1913, i, p, 587. For the chemistry 

 of tannins, especially with reference to an attempted synthetic production, see 

 Fischer: Jour. Amer. Chetn. Soc, 1914, xxxvi, p. 1187. 



