42 



BULLETIlSr 70O, U. S. DEPAETMEN-T OP AGEICULTUEE. 



length, and stem height, in the aspen-fir association, and (2) tlie rela- 

 tively high water requirement for the production of a unit of dry- 

 matter in the oak-brush type. 



In the case of peas, the number of leaves produced in the aspen-fir •: 

 type, as compared with the oak-brush and spruce-fir tj^pes, respec- 

 tively, is approximately in the ratio of 4, 2, and l.T. The leaf length ! 

 of wheat shows a ratio of about 2, 1, and 1.3 in favor of the aspen-fii- , 



i 



/ 



|53 

 \ 



/ 

 / 

 / 



\ 



\ 

 \ 





s^60 ^^ 



/ / 





626 







28 







S280 

 26 





/ ^v 







3990 







300 





28e" 























Oak-brush 



/Ispen 

 L eaf length 



Spnuoe-F/n 



Number of leaves 



Wafer requirement per 



unit dry matter 



Fig. 21. — Water requirements and vegetative growth of wheat in the three climatic tj-pes. 



association. In the case of the brome grass practically the same 

 relations exist. 



In each instance the water requirement per unit of dry matter is 

 the highest in the oak-brush type. The fact that the plants were 

 grown for a longer period in the highest and middle stations would 

 naturally imply that they used more total water, but not necessarily 

 that they had a higher water requirement per unit of dry weight. A 

 comparison shows that in the case of wheat and peas the water 

 requirements are very nearly the same in the central and in the 



