INTERNAL TEMPERATURE OF LEAVES. 



267 



Table XXX.— January 19, 1907. 



In this case the red leaf shows a more striking difference, 

 attaining a temperature of 3"9° C. above that of the white leaf. 

 This great difference may perhaps be to some extent correlated 

 with the presence of two pigments in the leaf, chlorophyll and 

 the anthocyau masking it. The general result which seems to 

 be clearly indicated by these experiments is that the presence 

 of any pigment raises the internal temperature of the leaf 

 whether the pigment be red (anthocyan) or green (chlorophyll). 

 A yellow or white leaf remains at a lower temperature on 

 account of the lack of pigment. The experiments in fact seem 

 to show more clearly a purely physical effect, similar to what 

 would be obtained with inorganic bodies, than was perhaps to 

 be expected. 



The fact that the red pigment does cause a higher tempera- 

 ture than that attained in leaves lacking it is now clearly 

 established for thin leaves, as it had previously been for 

 succulent leaves by Stahl. Attention was now paid to the 

 question of the internal temperature of young flaccid and 

 coloured leaves compared with the mature green leaves of the 

 same tree. Here the question is complicated by the fact that 

 besides differences in colour in the leaves compared there are 

 great differences of texture. In the case of Amherstia nobilis, 

 for example, the mature leaf is green, stiff, with fairly thick 

 cuticle, while the young leaf is thin, flaccid, and pliable with 

 scarcely developed cuticle, red in colour and almost without 

 chlorophyll. 



7(1)09 ■ (35) 



