vni] THE SIGNIFICANCE OF ANTHOCYANINS 139 



growth is retarded by light and hence is protected by the pigment. 

 Similarly, Stahl considers the reddening of young shoots in temperate 

 regions in the spring to be protective against cold, whereas Ewart 

 considers the function to be protective for the chloroplast, since the 

 latter is more sensitive to light when the temperature is low. Reddening 

 of submerged plants in sugar-cultures Ewart explains as being due to 

 an unhealthy condition of the plant in which state it requires more 

 protection against light. 



Ewart concludes thus: 'There can be little doubt that, both in 

 the tropics and in temperate climes, the main and primary function 

 of the red dye, when present in exposed parts, is to act as a protection 

 against light of too great intensity; though in all cases its presence 

 at the same time confers upon the plant a slightly increased power of 

 absorbing heat. For calling attention to this latter possibility Stahl 

 deserves full credit from both the physiologist and the biologist: in 

 a few cases, such as in the horizontal leaves of shade plants having the 

 red colouration present on the under surfaces only, the relatively slight 

 heat-absorbing power of the dye may, by secondary adaptation, have 

 become its most important function." 



The latest work on the physiological significance of anthocyanin, 

 and undoubtedly the most accurate, is that published by Smith (420) 

 in 1909. This author determined the temperature of leaves in tropical 

 insolation in Ceylon, using a thermo-electric apparatus. The latter 

 was of the improved pattern which had been employed by Blackman 

 & Matthaei, and had the advantage that it could be used even in the 

 lamina of thin leaves and also for the internal temperature of leaves 

 in natural illumination. 



In the first of a series of experiments connected with this point 

 young leaves of Amherstia nobilis and Saraca indica were compared. 

 Both trees have young foliage of the pendent type we have previously 

 described. The leaves of Amherstia are of a deep brownish-red colour 

 due to the presence of anthocyanin, and after this pigment is removed 

 by a solvent, there is seen to be but a slight development of chlorophyll. 

 The leaves of Saraca are greenish-white and have, in the same way, 

 a small development of chlorophyll. Both leaves are also thin and 

 flaccid and hence form good objects for comparison. On exposing the 

 leaves and testing the temperature, it was found that the coloured 

 leaf of Amherstia reached a temperature of 2 C. higher than the leaf 

 of Saraca. Another experiment was conducted with a young red leaf 

 of Mesua ferrea as compared with a young leaf of Saraca indica. The 



