28 THE VEGETATION OF THE UNITED STATES. 



particulars so as to make it conform more closely to the distribution 

 of vegetation, using vegetation rather than additional rainfall data as 

 a basis, we would secure a map of great interest and value as a dehnea- 

 tion of the vegetation of the United States. This map would be of no 

 value for a correlational study, however, since it would be in inherent 

 and foreseeable agreement with the map of mean rainfall of the growing 

 season, which is very similar to all other maps of moisture conditions. 

 The drawing of this map would resemble in all particulars the con- 

 struction of the hfe-zone map of the United States, both with respect 

 to the manner in which it was made and with regard to its unsuita- 

 bility for our purposes. 



It may also be emphasized in this connection that, although the 

 temperature conditions and the moisture conditions of chmate are con- 

 sidered as distinct in analytical studies, yet they are not truly inde- 

 pendent of each other. Since evaporation and precipitation are so 

 largely influenced by temperature, neither the chart of rainfall nor 

 that of temperature is wholly without indications of the influence of 

 one condition upon the other. It frequently happens, for example, 

 that a region of low temperature is one of high soil-moisture content, 

 low evaporation, etc. These considerations will receive more attention 

 in Part II. 



