246 



PIGMENTS 



/ \ 



CH CH 



H 



\ / 



CO 

 Pyrone 



which dissolves in hydrochloric acid, forming an additive com- 

 pound of the formula 



H Cl 

 \X 



O 



CH 



II 

 CH 



\ 



\ 



CH 



CH 



CO 



the oxygen becoming tetravalent. Such additive compounds 

 of anthoxanthins with acids are easily dissociated and do not 

 occur in plants, though it will be seen on page 248 that in the 

 case of the anthocyanins analogous compounds do actually 

 occur naturally. 



REFERENCES. 



Kostanecki : "Bull. soc. chim. Paris," 1903, [3], 29, i-xxxvii. 



Perkin, A. G., and others: " J. Chem. Soc. Lond.," 1895,67; 1896, 69; 

 1897, 71 ; 1898, 73 ; 1899, 75, etc. 



Wheldale : " Proc. Camb. Phil. Soc.," 1909, 15, 137; " Biochem. J.," 1914, 

 8, 204, etc. 



ANTHOCYANINS. 



Occurring in the cell sap, often in sufficient quantity tc 

 mask entirely the green colour of the chlorophyll, are a 

 number of pigments, other than chlorophylls, belonging to 

 various classes of chemical compounds. 



Under the collective heading of Anthocyanin are included 

 a number of such pigments of a blue, red, or violet tint occur- 

 ring in the flowers, fruits, or leaves of many plants.* Th( 

 first representative ' of the class to be isolated in a state of 

 purity by Willstatter and Everest-)- was Cyanin, the blu< 



* An historical account of our knowledge of these pigments is given b) 

 Everest in " Science Progress," 1915, 9, 597. See also Wheldale : " The Antho- 

 cyanin Pigments of Plants," Cambridge, 1916. 



f Willstatter and Everest : " Annalen," 1913,401, 189, 



