10 THE COCO-NUT 



TEMPERATURE (c.) 



Hour. 



In Shade. 



In Sun. 



In Leaf. 



7 A.M. 



20-3 



21-8 



21-9 



8 „ 



24-3 



25-2 



27-4 



9 „ 



26 



30-7 



33-1 



10 „ 



26-9 



32 



35-4 



11 „ ' 



27-8 



31-5 



34-7 









(light cloud) 



12 M. 



28*3 



34-7 



37-7 



1 P.M. 



28 



30 



31-5 









(cloudy) 



2 „ 



28-5 



31-5 



38 



3 „ 



28-8 



31 



36-7 



4 „ 



28-6 



30-6 



36-4 



5 „ 



27-7 



30 



34 



6 „ 



26-6 



27-6 



28-5 



With conditions as they were on this day, a surface 

 of water at the temperature of the leaf in the sun at 

 noon would evaporate about three times as much as 

 a surface at the shade temperature. The increase in the 

 evaporation from a leaf is greater still, provided that as 

 transpiration goes on the supply of water is kept up. 



If we now take up the actual rate of evaporation of 

 the water from the leaves, we find that beginning early 

 in the morning there is practically none. The tempera- 

 ture is low, the air is moist and usually still, and the 

 stomata are at first closed. Under the influence of the 

 light the stomata open, the air warms enough so as to 

 no longer be saturated with moisture, and the transpira- 

 tion gradually increases. This increase goes on for 

 several hours. If it were possible for the roots to take 

 up water and furnish it to the leaves as fast as it could 

 be evaporated, there would be a steady increase in 

 transpiration up to 1 o'clock or possibly later, as up to 

 this time the factors which promote it usually operate 

 with more and more intensity. But against this steady 

 increase in the transpiration there operates the fact that 



