CLIMATE AND PLANT GROWTH. 



43 



highest types, while brome grass shows a greater demand for water 

 in the spruce-fir type than in the aspen-fir type. All three species ex- 

 hibit a markedly interesting relation of development to water re- 

 quirement, namely, that the lowest water requirement for the 

 production of a unit of dry matter is invariably associated with the 

 most luxuriant growth. Further, figure 8 shows that the evapora- 



Oak-brueh /Ispen Spruce-F/'r 



— Average stem length 

 — — lA/afer requiremen t per 



unit dry weight 

 Number of /eaves 



Fig. 22. — Water requirements and vegetative . growth of Canada field peas in the three 



climatic types. 



tion curve, corresponding to the period of growth of the plants, 

 slants in the opposite direction from those of the development of 

 the plants as platted in figures 21, 22, and 23. In the oak-brush type, 

 where the water requirement is highest, evaporation is most intensive. 

 The data on the relative development of the plants in the type 

 stations and the corresponding water requirements are especially 

 important, since they represent vegetative activities throughout the 



