CLIMATE AND PLANT GROWTH. 



27 



does the mercury column of the sunshine recorder of the Weather 

 Bureau type. 



The data seem to warrant the statement that the use of atmometers 

 in obtaining sunshine duration affords quite as reliable a record as 

 does the more costly Marvin sunshine recorder. Of course, the 

 impossibility of operating atmometers when the temperature drops 

 below freezing makes them of value only during the growing sea- 

 son. Where it is desired merely to obtain a summary of the sunshine 

 record, it is necessary to read the instruments only about twice per 

 month, whereas the Marvin recorder must be read daily. 



OCT. NOV. DEC. JAN FEB. MAR. APR. MAY JUN. JUL. AUG. SER 

 FIG. 11. Monthly mean temperatures October, 1915-October, 1916. 



COMPARISON OF THE CLIMATIC CHARACTERISTICS OF THE 

 THREE PLANT TYPES. 



TEMPERATURE. 



For purposes of comparison there is probably no better way of 

 showing differences in temperature in the type stations than to give 

 the monthly mean temperature for each station. This is shown 

 graphically in figure 11. Throughout the year the mean monthly 

 temperature is appreciably lowest in the spruce-fir and highest 

 in the sagebrush-rabbit-brush type. In general, the slopes of the 

 mean-temperature curves of all the climatic types are similar, and 

 this is especially true for the main growing season, from June to 

 September, inclusive. 



In the monthly range in temperature for the respective types there 

 are even greater contrasts than in the daily means. The range in the 

 monthly temperatures is shown in figure 12. These temperatures 

 differ most notably from those given in figure 11, representing the 

 monthly means, in (1) the similarity in vertical form and proximity 



