FUNCTION OF ANTHOCYANIN 255 



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 [Elodea] 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 Hczmatococcus and 

 the resting spores of many Algae. 



Ewart does not think that the pigment is an accidental 

 occurrence in all cases, for in Elodea it is not formed in diffuse 

 light ; on the other hand, in the beetroot it probably has no 

 special function, and may be a waste product of metabolism. 



Shibata J and his colleagues found that derivatives of flavones 

 are almost universally distributed in sub-aerial plants, alpine 

 and tropical plants particularly so. They conclude that the 

 presence of these substances, especially when in the peripheral 

 tissues, absorb the ultra-violet rays, and thus are protective. 

 Rosenheim supports this view since he found that Leonto- 

 podium alpinum, the Edelweiss, when grown in London, con- 

 tained but a quarter the amount of the substances in question 

 as compared with plants grown in the Alps. 



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

 f See Thoday and Sykes : " Ann. Bot.," 1909, 23, 635. 

 % Shibata : " Bot. Mag. Tokio," 1915, 29, 118 ; Shibata, Nagai, and Kishida : 

 " J. Biol. Chem.," 1916, 28, 193. 



Rosenheim : " Biochem. Journ.," 1918, 12, 283. 



