140 THE SIGNIFICANCE OF ANTHOCYANINS [CH. 



red Mesua leaf registered a temperature of 2-8 C. higher than the 

 Saraca leaf. 



It was next found by comparing green and white leaves, that a green 

 leaf also reaches a higher temperature than a white one. Hence it 

 seems clear that any pigment, either chlorophyll or anthocyanin, raises 

 the temperature of the leaf, and that the simultaneous presence of 

 anthocyanin and chlorophyll in the leaf will raise the temperature 

 considerably above that of a leaf without either pigment. The latter 

 point was demonstrated in a comparison between a green and white 

 leaf of Caladium sp. and a red and green leaf of the same genus, the 

 electrodes being placed in the green and white leaf where there was 

 little chlorophyll. The red and green leaf then showed a most striking 

 rise of 3-9 C. above the green and white leaf temperature. 



Attention was finally given to the differences between the temperature 

 of young flaccid and coloured leaves as compared with older green 

 leaves from the same tree. With Saraca indica, a mature green leaf 

 showed a difference of 4 C. above a young colourless leaf. When, 

 however, a young leaf of Theobroma Cacao which is red, was compared 

 with a mature green leaf, the young leaf showed a difference of 3-5 C. 

 above the mature leaf, and this one would suppose to be due to the 

 presence of the anthocyanin. On the other hand, comparisons of young 

 red leaves with mature green leaves of Amherstia nobilis, resulted in 

 a decidedly higher temperature in the mature leaf. 



"Thus," Smith concludes, "it seems, that we have a series beginning 

 with Saraca indica, in which anthocyan is almost absent, and in which 

 the mature leaf is always higher in temperature than the young leaf. 

 Then comes Amherstia nobilis with a brownish-red colour, in which the 

 mature leaf is, as a rule, only slightly higher in temperature than the 

 young leaf. Lastly, we have Theobroma Cacao with the young leaf an 

 intense pinkish-red and the mature leaf lower in temperature than 

 the young leaf. 



"No doubt the relative temperatures of mature and young leaves 

 are to be correlated with the amount of anthocyan in the young leaf. 

 The young leaves, without this pigment, would be always cooler than 

 the mature leaf, as is the case in Saraca indica. The presence of more 

 or less anthocyan produces a temperature in the young leaf, which 

 almost reaches (Amherstia} or exceeds (Theobroma) the temperature of 

 the mature leaf. Thus the general tendency of these results is to confirm 

 and extend Stahl's conclusion that the presence of anthocyan tends to 

 raise the internal temperature of the leaf. What biological advantage. 



