226 TRANSACTIONS OF THE [Sess. lxxxi 



Botanists are far fi'om agreed upon this subject of 

 anthocyanin, and conclusions based upon the same set of 

 experiments are sometimes diametrically opposed. In part 

 the conflict of opinion seems to be due to the tendency of 

 workers to see in one activity the only significance of the 

 pigment. As I read the facts of distribution of anthocyanin 

 in Nature, and those of experimental work, I receive the 

 impression that these pigments, having a definite absorptive 

 relation to light and to heat — whatever else they may do,— 

 may operate differently in accordance with the position in 

 which they occur. 



Their occurrence in the vouno- unfolding leaves of the 

 bud, particularly in tropical and warm-country trees, is 

 the starting-point for the suggestion of their use as a 

 screen to the chloroplasts against intense insolation; and 

 if to the chloroplasts also to the cytoplasm, whether chloro- 

 plasts be present in an organ or are absent, as in the case 

 of the anther. Much experimental Avork has been carried 

 out to test this hypothesis, which I believe is well founded. 

 It is obviously difficult to apply this interpretation to our 

 Rhododendron seedlings where the pigments are on the 

 under and concealed surface of the leaves, which are not 

 in danger of intense insolation. 



The frequent abundance of anthocyanin pigments on 

 leaf-petioles, on stems, on veins, has been advanced in 

 support of the suggestion that they have relation to 

 transport of plastic material ; their activity would be that 

 of protecting enzymes fi-om harmful solar rays, and thus 

 aiding metabolism and food-transference. This view is, 

 after all, complementary of the other. There is nothing 

 antagonistic. A screen to the cytoplasm itself against 

 intensity of light rays may well be one also to its products 

 against rays of particular f|uality. In the case of our 

 Rhododendron seedlings such activity of tlie pigments in 

 relation to tlie limited ainount of light reaching the leaves 

 is quite possible. 



Then there is the heat-relation of the pigments. That a 

 light-relation is not the only one is clearly shown by their 

 presence at the root-tips deep in the soil of so many peat 

 plants. Are they not to be regarded as heat-regulators 

 within the plant ? Such a conception by no means negates 



