254 PIGMENTS 



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 Hcema- 

 tococcus to turn red. 



Finally, the work of Wheldale* 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 246. 



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 

 in plants very remote phyletically one from the other; and 

 that chemically this pigment may not always be exactly the 

 same. Further, as its appearance seemingly depends upon 

 the immediate metabolic condition of the plant, and so in 

 some cases may be sporadic, whilst in other instances it is 

 characteristic of the species or variety or form, cafe must be 

 exercised in ascribing to it a definite function. Its presence 

 may be due to nothing more than the particular metabolic 

 sequence ; in other words, an accident, which, in some ex- 

 amples may be a lucky one for the plant. 



It is, of course, not surprising to find that several opinions 

 have been put forward to explain its presence. 



According to Pick the dye is a filter to separate from the 

 light entering the leaf certain rays which would be deleterious 



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

 IQII, I, 10. 



