Periodical Literature. 577 



data would be of great value to the agriculturist and to the for- 

 ester. The weather bureau is officially a part of the Department 

 of Agriculture, being one of the largest bureaus of the Depart- 

 ment, yet its main activities have never been primarily directed 

 towards the relation between agriculture and climatology. The 

 data of precipitation should be linked with data upon soil con- 

 ditions. Upon the water extracting power of the aerial environ- 

 ment, the climatic data of the weather stations is of no use. For 

 these purposes there should be more rural stations with the re- 

 cording instruments in other situations than high buildings. 



The temperature data in relation to plant growth should be for 

 the frostless season, but actual data of the mean length of the 

 frostless season in the United States have never been published. 

 Compiling data from Bigelow's tables of daily normal tempera- 

 tures throughout the year, Livingston has summarized the tem- 

 peratures during the frostless season, taking as a starting point 

 32° F., and has plotted them in thousand degrees upon a map. 

 The lines of temperature summation divide the country into 

 zones having in general an east and west direction with a south- 

 ward displacement along the two mountain systems. The tem- 

 perature indices range from 3,000 to 13,000 degrees during the 

 frostless season. The average daily precipitation (in hundredths 

 of an inch) plotted upon a map of the United States divides the 

 country into north and south trending zones, in general perpen- 

 dicular to the temperature zones. The amount of mean daily 

 evaporation plotted upon a map also divide the country into 

 north and south belts. The chart indicating the difference be- 

 tween the mean daily precipitation and the mean daily evapora- 

 tion during the growing season is the most remarkable since it 

 shows that in most of the United States evaporation exceeds 

 precipitation. Of course, the data for the last two mentioned 

 charts are very meagre, and they are put forward by the author 

 simply as suggestions as a proper line of procedure in the study 

 of vegetational characteristics in relation to climate. If further 

 study along these lines should demonstrate that evaporation really 

 exceeds precipitation during the growing season, then we would 

 have a powerful argument for the conservation of soil water. 



C. D. H. 



Proceedings of the American Philosophical Society. Vol. 52, No. 209, 

 April, 1913, pp. 257-279. 



