62 



BULLETIN 700, U. S. DEPARTMENT OF AGRICULTURE. 



temperature index and the evaporation rate were also expressed as 

 average daily rates in order to make these climatic factors com- 

 parable to the plant measurements. The data were recorded prac- 



Phys/o/og/ca/ Temperature 



efficiency 



Wheat 



Brome-grass 



Evaporation 



FIG. 34. Relation between increments of leaf expansion, evaporation rate, and tempera- 

 ture, aspen-fir type. 



tically simultaneously at about 10-day intervals in each association. 

 The first measurements here recorded are for June 22 10 days after 

 establishing the.potometers. 



TABLE 18. Effect of evaporation and temperature on leaf expansion of wheat 

 and bronie grass in type stations at about 10-day intervals, beginning June 

 22, through growing season. 



