PHYSIOLOGICAL SIGNIFICANCE 247 



the action of an oxidase upon glucosidal flavones or similar 

 bodies. 



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 alkalis 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 anthocyan 

 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, care 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 

 to the translocation of the starch. Keeble found that in leaves 

 which had the dye on one side but not on the other, the differ- 

 ence in temperature due to the anthocyan was about 2° C, 

 and he concluded that it may be of value as a protective 

 mechanism against the heating effect of strong sunlight. 



Stahl * thought that it absorbs heat and so increases trans- 

 piration, especially in the case of tropical plants. Ewart points 

 out that, although this might sometimes be of value, if it were 

 the primary function it would naturally be expected that an- 

 thocyan would absorb the heat rays more particularly. Also 



* vStahl : " Ann, Jard. Bot, Buitenzorg," 1896, 13, 137. 



