256 PIGMENTS 



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 sup- 

 plied by these veins. Boodle then experimented with species 

 of Oenothera ; all the species examined were not equally 

 responsive, but in the case of O. 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 carbohydrates 

 which leads to the development of anthocyanin. In this con- 

 nexion the work of Linsbauer * may be referred to. 



That the presence of anthocyanin is connected with nutritive 

 processes there can be no doubt, but other substances besides 

 sugar may come into play ; thus Dendy observed that the ad- 

 dition of protein to the water, caused green plants of Hama- 

 tococcus to turn red. 



Finally, the work of Wheldalef on colour inheritance in 

 flowers, points to the conclusion that anthocyanin is a product 

 of the action of an oxidase upon glucosidal flavones, a view 

 which is entirely borne out by the chemical evidence outlined 

 on page 248. 



Reactions. 



1. Soluble in water, alcohol, and ether. 



2. The solution is coloured according to the reaction, red 

 in the presence of acid and blue when the medium is made 

 alkaline. 



3. Strong alkalies decolorize the solution. 



4. Basic lead acetate gives a green precipitate. 



5. With salts of iron, a green or blue coloration results. 



Physiological Significance. 



In considering the physiological significance of anthocyanin 

 it must be borne in mind that the substance may occur in 

 almost any organ of a plant, from the root to the flower, and 



* Linsbauer: " Oestr. Bot. Zeit.," 1901, 51, i. 



+ Wheldale: " Proc. Camb. Phil. Soc.," 1909, 15, 137; "Journ. Genet.," 

 1911, I, 10. 



