REVIEWS 61 



days, and the data seemed to warrant the statement that the use of 

 atmometers to obtain records of sunshine duration are quite as rehable 

 as the more costly sunshine recorder. 



The author presents a detailed comparison of the climatic character- 

 istics of the sites where the potometers were located and summarizes 

 them on different bases. It is a comparatively easy matter to measure 

 the growth of plants and to measure the separate site factors to which 

 they are subjected. The difficulty comes in correlating growth with 

 these factors. The most interestinK, but also in many respects the 

 most unsatisfactory, part of the bulletin is the attempt on the part of 

 the author to correlate growth with the environmental factors. An 

 analysis is made, first, of the relative development of the plants at each 

 station and their corresponding water requirement ; second, of the rela- 

 tive development of the plants at each station and the amount of avail- 

 able heat ; third, the effect of evaporation and temperature on the 

 production of dry matter and on the growth of the plant as a whole. 



The temperature factor in the respective stations for the periods that 

 the potometers were under observation was summarized as follows : 



(a) By physiological temperature coefficient. 



(b) By the sum of the means above 40° F. 



(c) By the sum of the daily means. 



It is worthy of note that the summed physiological temperature co- 

 efficients derived by Lehenbauer's method bore practically the same 

 relation to each other in the respective type stations as the sums of the 

 means above 40° F. This relation, however, did not hold true in the 

 summation of the daily mean temperatures. 



The summation of water requirements in the respective stations was 

 based upon the water required to produce during the growing season a 

 unit weight of dry tops of the standard plants. The most striking 

 features brought out in the graphs, representing the summation of 

 water requirements, were the greater vegetation development per unit 

 of water consumed in the aspen-fir type and the relatively high water 

 requirement for the production of a unit of dry matter in the oak- 

 brush type. 



In order to determine the relation of the water requirements of the 

 standard plants to evaporation and temperature in the type stations, 

 the water used per unit of dry matter through practically the entire 

 growing season was in each case divided by the evaporation for the 

 corresponding period. The value of the quotients obtained was found 

 to be highest in the oak-brush type, intermediate in the aspen-fir type, 

 and lowest in the spruce-fir type, and the conclusion was reached that 



