CLIMATE 'AND PLANT GROWTH. 



53 



EFFECT OF TEMPERATURE AS INDICATED BY WATER REQUIREMENT PER UNIT OF 



LEAF AREA. 



The water requirements per unit of area of the chief food manufac- 

 turing agents of plants the leaves may be used as an index of the 



63 



99 



660 



60 



f* 



Oak-brush 



Aspen 



Spruce-fir 



for appearance of heads 



Temperature above 4O 



Average c/ai/y mean temperature 



PIG. 29. Relation of temperature to time of first appearance of heads of brome grass. 



efficiency of the leaves as users of water. The leaf length is used in- 

 stead of actual leaf area in the data given below, since, as has been 

 previously shown, it is proportional to the actual area. 



