242 PIGMENTS 



and observations on the production of anthocyan under con- 

 ditions, such as injury, etc., which tend to interfere with the 

 proper translocation of the glucosidic flavones. 



REFERENCES. 

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

 Perkin, A. G., and others: "J. Chem. Soc. Lond.," 1895, 67; 1S96, 69; 

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



Wheldale ; " Proc. Camb. Phil. Soc," 1909, 15, 137. 



ANTHOCYANIN, PHYCOERYTHRIN, AND 

 PHYCOPHAEIN. 



Occurring in the cell sap, often in sufificient quantity to 

 mask entirely the green colour of the chlorophyll, are a 

 number of pigments, other than chlorophylls, belonging to 

 various classes of chemical compounds. 



These substances are not completely understood, either 

 with regard to their chemistry or to their physiological signifi- 

 cance. They form, however, so conspicuous a feature in 

 vegetation that a brief consideration of them is justified. 



ANTHOCYANIN. 



The occurrence of a red, blue, or purple pigment, either 

 dissolved in cell sap — the exact colour depending on the -acid, 

 alkaline, or neutral reaction of the cell sap — or, less frequently, 

 in the form of needle-shaped crystals, as in the case of Del- 

 phinimn ajacis, is a common phenomenon, and is generally 

 ascribed to the presence of the pigment anthocyan, or antho- 

 cyanin. These pigments are commonly associated with colour- 

 ing matters of the nature of flavones and xanthones. It is, 

 however, doubtful whether all such colorations are due to these 

 substances ; thus Molisch found that the red colour assumed 

 by the leaves of the aloe, on exposure to high insolation, is 

 due to the formation of carotin within the chloroplasts. 



The presence of anthocyan is due to many causes, light, 

 especially when of high intensity, being important. For 

 example, apples and other fruits and also the vegetative 

 organs of certain plants will not assume a red colour if kept 

 in darkness ; on the other hand, light does not appear to be 

 of such importance in the case of the roots of the beet. 



