vm] THE SIGNIFICANCE OF ANTHOCYANINS 133 



is these same rays which cause the formation of anthocyanin. Finally, 

 it was shown that red leaves always contain more diastase than green. 

 From these results the authors conclude that anthocyanin has a 

 protective action on diastase. 



The third theory which has been so largely supported by Stahl 

 (405) is based on the power shown by anthocyanin of converting light 

 rays into heat. Kerner, as previously mentioned, had the idea of this 

 function of anthocyanin, but Stahl laid stress on a special aspect, viz. 

 that of accelerating transpiration in red leaves. 



Stahl, however, was by no means the first to suggest a connection 

 between light absorption and transpiration. As early as 1879-80, 

 Comes (388, 389, 390) published the results of work on the effect of 

 light on transpiration. He used pot plants which were enclosed in a 

 zinc case with a glass front, and the loss of water was determined by 

 weighing. The plants were also exposed to differently coloured light 

 obtained by using potassium bichromate, ammoniacal copper, and 

 alcoholic chlorophyll solutions. The transpiration of various coloured 

 corollas was observed, the absorption bands of the pigments being also 

 ascertained. From his experiments Comes arrives at the following 

 conclusions. Transpiration is affected by light as well as by physical 

 conditions; other things being equal, a plant transpires more in the 

 light than in the dark, and the effect of light is proportional to its 

 intensity. Light favours transpiration only in so far as it is absorbed 

 by the colouring matters, and thus, that organ transpires most which 

 is most highly coloured. (This point was demonstrated by the coloured 

 corollas; those of which the pigment showed absorption bands in the 

 greatest number, breadth and intensity, transpired most strongly.) 

 Moreover, the rays which are most favourable for transpiration in a 

 coloured organ are those which are most absorbed by it. Hence the 

 transpiration of an organ is slightest under the influence of light which 

 is of the same colour as the organ itself, and strongest when under the 

 rays of the complementary colour. We have here then in Comes' 

 results the basis of Stahl's hypothesis, that the red pigment of leaves 

 brings about additional absorption and heating of the leaf, and conse- 

 quently greater transpiration. 



In addition, Kny (397) claims to have shown, by means of a simple 

 experiment, that red leaves do attain a higher temperature than green. 

 Kny filled tw T o parallel-sided vessels with green and red leaves respec- 

 tively of the same plant, and then filled up the vessels with water. 

 When these were exposed to light, the heat rays being cut off by alum 



