FUNCTION OF ANTHOCYANIN 257 



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 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. 



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- 

 thocyanin would absorb the heat rays more particularly. Also 

 Ewart cites his observations on Elodea against Stahl's view, 

 and remarks that " since the plants [Eiodea] are submerged, it 

 cannot possibly be for the purpose of increasing what is non- 

 existent, i.e. transpiration, nor can it perceptibly raise the tem- 

 perature of a submerged plant ". The first argument may no 

 longer be valid, for it appears that a transpiration current may 

 exist in submerged aquatic plants.f 



Ewart believes that anthocyanin is to protect the chlorophyll 

 against the action of too strong light. He gives experimental 

 data in support of his view, and cites the observations of 

 Schroder and Klebs to the effect that the pigment is of im- 

 portance in protecting the chlorophyll in Hcemaiococcus and 

 the resting spores of many Algae. 



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



+ See Thoday and Sykes : " Ann. Bot.," lyog, 23, O35. 



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