ANTHOCYANINS 34 1 



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 

 temperature of a submerged plant." The first argument may 

 no longer be valid, for it appears that transpiration current 

 may exist in submerged aquatic plants. f 



Ewart believes that anthocyanin is to protect the chloro- 

 phyll 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 importance in protecting the chlorophyll in 

 HcEfnatococcus 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$ 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 Leontopodium alpinum, the Edelweiss, when grown in 

 London, contained but a quarter the amount of the substances 

 in question as compared with plants grown in the Alps. 



Wulff considers that the pigment is of value in the absorp- 

 tion of extra radiant energy, and is of great importance in 



* Stahl : "Ann. Jard. Bot. Buitenzorg," 1896, I3t i37- 

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

 I Shibata : " Bot. Mag. Tokio," 1915. 29. "8 ; Shibata, Nagai, and 

 Kishida : " J. Biol. Cham.," 1916, 28, 193. 



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



