34 STUDIES IN THE VEGETATION OF THE STATE 



perature differences between the prairie formation on the 

 one hand and thiclcet and deep woodland formations on the 

 other range from .2°-5° during the early spring months, 

 and from 2°-12° 15° during the summer months. 



Soil temperatures are inyariably higher in I than in II, 

 III, or IV. During the spring and autumn these differ- 

 ences range from 2°-5°, while in midsummer it is not un- 

 common for the soil temperature of the prairie to range 

 12 "-20° higher than corresponding temperatures in thickets 

 and woodlands. Soil temperatures of location I show great- 

 est variations, 10°-20° in twenty-four hours being not infre- 

 quent. Similar temperatures in woodlands and thickets are 

 relatively stable, the changes being gradual and of a less 

 degree. It is also to be noted that soil temperatures taken 

 at a number of stations in the same formation show little 

 variation if conditions are similar. Immediately after a 

 heavy precipitation, temperatures of the soil in all forma- 

 tions are observed to have approached almost a common 

 degree. 



Psychrometer data indicate the least amount of atmos- 

 pheric humidity in the prairie formation and the greatest 

 amount in thickets and deep woodlands; in this relation, 

 as would be expected, open woodlands are intermediate. As 

 a rule, the wet-bulb thermometer registered .2°-3° lower 

 at a height of one meter than at the earth's surface, thus 

 indicating a greater evaporation of the water particles from 

 the bulb and hence less humidity in the atmosphere at this 

 height. The dry-bulb thermometer recorded in most cases a 

 temperature of .2°-2.5° higher one meter above than at the 

 earth's surface. These conditions are found to be true, in 

 general, for the various formations, and they explain to a 

 considerable extent the habits of certain plants of our flora, 

 which tend to develop mesophytic leaves near the ground 

 and xerophytic leaves above. It goes without saying that, 

 when the atmosphere is laden with moisture, little or no 

 difference is observed between the wet- and dry-bulb ther- 



