PAPERS ON BOTANY 123 



the long slopes which lead directly down to it from the Con- 

 tinental Divide, here some 2500 feet above it, but less than 

 ten miles distant. 



Both localities are exposed to high winds, but the moun- 

 tain habitat particularly so. During the colder months of the 

 year in particular do westerly winds of high velocity and 

 great desiccating power sweep down from the Continental 

 Divide. 



SOIL CONDITIONS 



The soil conditions are very diverse. The rich agriculture 

 of Illinois is associated with a prairie soil of almost exhaust- 

 less fertility. It is a dark, heavy loam or silt of rather fine 

 texture, possessing, as has been shown by Harvey 3 , a large 

 water holding capacity as indicated by a high wilting coeffi- 

 cient. On the contrary, the soil of Boulder Park is lacking in 

 fertility and coarse in texture, consisting of glacial gravels 

 with a very small percentage of humus. No determination of 

 its water holding capacity nor of its wilting coefficient have 

 been made, but they are known to be low, since investiga- 

 tions of actual soil moisture conditions by Ramaley 4 show, dur- 

 ing July, from 1.5 to 5.5 per cent of moisture in the drier por- 

 tions, and only 1 1 per cent of moisture in the soil of the meso- 

 phytic meadow. In and about the shallow lakes there are 

 small accumulations of peat and in portions of the sedge-moor 

 the accumulation of humus has been rather considerable, so 

 that in spots the soil becomes comparable in its organic con- 

 tent with that of corresponding areas in Illinois. 



It seems certain that during the summer season the soil of 

 this mountain habitat, except where it is at or near the water 

 table, is deficient in soil moisture and this deficiency is reflected 

 in the xerophytic aspect of its vegetation. It is interesting to 

 note in this connection that Harvey 2 has found that the soil 

 moisture in the Chicago prairie falls below the wilting coeffi- 

 cient at midsummer. 



Summarizing the comparison of climate and soil factors 

 in the two grasslands it will be seen that they differ widely 

 in respect to altitude, length of growing season and in soil 

 fertility and texture, but agree in possessing conditions of 

 relatively low atmospheric humidity, in being exposed to high 

 winds and in having a deficiency in the supply of soil mois- 

 ture at least during the weeks of midsummer. Further the 

 precipitation in the two habitats is practically the same in 

 amount, although a closer study would probably show that it 



