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, 

 ki 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. 



Type. 



Oak-brush 

 Aspen-fir. . 

 Spruce-fir . 



Plant. 



Wheat 



Peas 



Brome grass 



Wheat 



Peas 



Brome grass 



Wheat 



Peas 



Brome grass 



Average 

 stem height 

 of peas and 

 leaf length 



of wheat 



and brome 



grass. 



Mm. 

 3,990 

 4,781 

 15,980 



8,560 

 11,863 

 22, 290 



5,280 



5,584 

 8,114 



Number 

 of leaves. 



28 

 206 

 125 



53 

 398 

 144 



26 

 166 

 81 



Water 

 require- 

 ment 

 per unit 



dry 

 matter. 



Grams. 



779 

 803 



288 

 368 

 516 



300 

 345 



756 



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 



