Time. 



A.M. 



11.46 

 11.47 



11.54 

 11.56 



INTERNAL TEMPERATURE OF LEAVES. 



Table XXV.-^January 27, 1906. 



Leaf of Acalypha tricolor. 



Conditions. Temperatui-e 



ot Leaf. 



Still, briglit sun .. 42-9 



Fairly strong breeze, bright 



sun .. 35-9 



Still, bright sun . . 41-7 



Do, .. 43-5 



255 



Excess 

 over Air. 



14-9 



7-8 

 13-7 

 15-5 



Time. 



A.M. 



10.55 

 10.56 



10. 5o 

 10.56 



Table XXVI.— January 21, 1907. 



Mature leaf of Theobroma Cacao. 



Conditions. 



Still, bright sun 



Strong breeze, bright sun 



Temperaturo 

 of Leaf. 



37-2 

 30-9 



Young red leaf of Theobroma Cacao. 



Still, bright sun ,. 40-3 



Strong breeze, bright sun ' . . 30-0 



Excess 

 over Air. 



10-7 

 4-4 



13-8 

 3-5 



The last example furnishes the extreme case of effect of 

 breeze, 10° C. difference in temperature being caused in the 

 young red leaf of cacao by a sudden strong gust of wind. 

 Summing up, it may be said that breezes of various strengths 

 reduce the temperature in thin leaves immediately from 

 2°-10° C. below what they attain in still air. It only remains 

 to point out how important such air movement is in natural 

 conditions in reducing leaf temperature. There are few days 

 when some sort of breeze is not present, and even on com- 

 paratively still days the occasional Ught airs which spring up 

 have an important effect in reducing leaf temperature. 



Effect of Colour (historical). 



A large number of observations were made on the internal 

 temperature of leaves of different colours, especially on those 

 coloured red with anthocyan. The subject of the significance 

 of such red colouring matters has attracted considerable 

 attention. The method followed by observers on this matter 

 has almost ahvays been to regard the presence of anthocyan 

 as an adaptation advantageous for some purpose, and then to 



