68 



BULLETIN 700, U. S. DEPARTMENT OF AGRICULTURE. 



found to be highest in the oak-brush type, intermediate in the aspen- 

 fir type, and lowest in the spruce-fir type, the curves in the case of 

 each species following in a general way the physiological tempera- 

 ture indices. 



/3 



2473.7 



<0 



9 

 8 

 7 

 6 



/58 



^Os 



730.S 



7t 



Oak-brush 



Aspen-rir 



Physiological temperature 



e fficiency 

 Brome -grass 



Spruce-Fir 



FIG. 37. Relation of the quotient of water requirement and evaporation C^ r - *M 



temperature. 



to 



On the basis of the agreements shown, it may be concluded that 

 the water requirement of these plants is determined largely by 

 evaporation and temperature. Hence it is evident that in localities 

 of limited rainfall, high evaporation, and high temperature values, 

 agricultural pursuits, even where the most drought-resistant species 



