400 



Cannon: Transpiration of Fouqujeria 



3 



Whether the amount 

 of evaporation for 1904 

 and the relation of that 

 amount to the rainfall 

 of the year as given are 

 exact expressions of the 



true ratio and of the 

 actual amount does not 

 matter for the present — 

 the striking fact, which 

 is inadequately shown 

 by the illustration, is 

 that a really small de- 



3 crease in the annual 

 rainfall may be a most 

 important fact in the 



^ nicely balanced life rela- 

 tions of desert plants. 



A climatic condition, 

 the relative humidity, 

 which is closely asso- 

 ciated with the rainfall 

 and thus with the rate 

 of transpiration, may be 

 passed over in few words. 

 As the seasonal rainfall 



tc 





u 



O 



^3 

 u 



O 



CJ 



cu 



2 



K 



(4 



^ was less than usual, so 

 also the average relative 

 humidity was probably 

 correspondingly lower. 

 What the departure from 



the normal may 



have 



been, however, I have 

 no observations at hand 

 to show. Certain it is 

 that the humidity at 

 times was very low, as 

 for instance during the entire week ending July 4 it did not even 



