52 



BULLETIISr 700, U. S. DEPARTMENT OF AGRICULTURE. 



The difference in the time for the plants to reach approximately 

 the same stage of maturity in the type stations may account, in part 

 at least, for the difference in the character and composition of the 

 vegetation in the respective types as well as for failures to establish 

 exotic and indigenous species adapted to types of higher effective tem- 

 peratures. In the spruce-fir type only those species which can com- 



/6 



Oak-Brush Type Aspen -Fir 8pruce~Fir 



Days For Appearance Of Heads 



Temperature Above 40 F. 



Averaqe Dally Mean Temperatare 



Fig. 28. — Relation of temperature to time of first appearance of heads of wheat. 



plete their developmeijt to maturity in minimum time, provided, of 

 course, that their perpetuation is dependent wholly or primarily on 

 seed, are conspicuously in evidence and of economic importance. 

 This tendency toward early maturity is evident, for example, in the 

 case of mountain brome grass, less days beirg required in all type 

 stations for its flower production than for that of peas and wheat. 





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