56 



TRANSPIRATION IN A DESERT PERENNIAL. 



Proper substitution in equation 2 gives: 



[(20.66) (.41) + (2.23) (X) +6.80] [6.3] = (14.51) (7.24) 

 .*. specific heat of leaves, X = .64. 



Proper substitution in equation 3 gives: 



[(20.66) (.41) +6.80] [.50] = (2.23) (.64) (X) .'. X = 5.3. 

 Therefore the temperature of the leaves was 



19.2+ 5.3 = 24.5, or 5.5 above air-temperature. 



EXPERIMENTATION. 

 EXPERIMENT XX. 



A series of leaf-temperature determinations was made from trees D and E. 

 The samples were taken every 2 hours, a period of 2 to 3 minutes elapsing 

 between the cuttings. The general appearance of the trees indicated that 

 tree E was nearer the stage of dropping its leaves than was D. 



TABLE 23. Temperatures for leaves from two trees urith the corresponding air-temperatures 



Experiment XX. 



9 6789 10 11 12 123456 



FIG. 25. Graph for leaf-temperature from two adult trees, plotted with air-tempera- 

 tures. Exp. XX. 



