CLIMATE AND PLANT GROWTH. 



41 



It is a noteworthy fact that the summed physiological temperature 

 coefficients and the sum of the positive temperatures; that is, those 

 above 40 F., bear practically the same relation to each other in the 

 respective type stations. This has also been observed to hold true, 

 in general, for shorter periods (fig. 20). Neither of these summa- 

 tions, however, agrees with the sum of the daily temperatures. As 

 will be shown elsewhere, both the physiological temperature coeffi- 

 cients and the sum of the positive temperatures show some relation to 

 growth and other plant activities. This does not appear to hold true 

 of the summation of the daily mean temperature. Because of the 

 corresponding slopes of the graph in figure 19 between the physio- 

 logical temperature summation and the sum of the positive tempera- 

 tures, either may be used for comparison with the plant-growth data 

 in the case of the batteries observed for the period in question. 



CORRELATION BETWEEN GROWTH AND ENVIRONMENTAL 



FACTORS. 



RELATIVE DEVELOPMENT OF THE PLANTS IN THE TYPE STATIONS, AND THE 

 CORRESPONDING WATER REQUIREMENTS. 



A summation of the data obtained for the development and water 

 requirements in the different type stations of wheat, peas, and brome 

 grass (based on dry weight of tops) is given in Table 12. These 

 figures represent the activities of the plants for 81 days in the oak- 

 brush type, 95 days in the aspen-fir type, and 91 days in the spruce- 

 fir type. The temperature indices and evaporation summaries for 

 the respective periods are given in figures 19 and 8. 



TABLE 12. Summation of growth and water requirements of plants developed 



in the type stations. 



The values given in Table 12 are platted in figures 21, 22, and 23, 

 The most striking features brought out in the graphs are (1) the 

 greater vegetative development, including number of leaves, leaf 



