340 PIGMENTS 



processes there can be no doubt, but other substances besides 

 sugar may come into play ; thus Dendy observed that the 

 addition of protein to the water caused green plants of 

 Hcematococcus to turn red. 



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, 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. 



The chief physical property of anthocyanin is its absorp- 

 tion spectrum. Engelmann found that it is complementary 

 to that of chlorophyll, the main absorption bands being in the 

 yellow and yellow-green, with minor ones in the blue end of 

 the spectrum. Questions relating to the energy relationship 

 between this and other pigments and chlorophyll are outside 

 the scope of the present consideration ; it may be mentioned, 

 however, that it has been stated that leaves containing 

 anthocyanin have relatively less chlorophyll than those which 

 have no red pigment. 



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 difference in temperature due to the anthocyanin was 

 about 2° C, and he concluded that it may be of value as a 

 protective mechanism against the heating effect of strong 

 sunlight. 



