44 



BULLETIN 700, U, S. DEPARTMENT OF AGRICULTURE. 



season. Hence these data appear to throw some light on the causes 

 of failure or success of experimental trials with plants in the types 

 represented. 



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Oa/c drus/i 



^spen 

 Leaf/engfh 



Spruce-f/r- 



A/umber of /eaves 



Wafer requjrcnnent per 



unit dry ma tier 



Fig. 23. — Water requirements and vegetative growth of brome grass in the three climatic 



types. 



THE EFFECT ON PLANT GROWTH OF DIFFERENCES IN THE AMOUNT OF HEAT- 

 AVAILABLE IN THE THREE TYPES. 



EFFECT OF TEMPERATURE AS INDICATED BY DIFFERENCES IN WATER EEQXTJREMENTS 

 BASED UPON STAGE OF DEVELOPMENT AND CONDITION OF CERTAIN AERIAL PARTS. 



The total effective heat units and length of growing season in the 

 types studied are such that only in the lowest type do the plants reach 



