32 A Study of the Vegetation of 



this station in the fir-tamarack community was 60 per cent., that 

 of the prairie and pines about 45 per cent. On August 14, 1914, 

 the water content at each station was found to be somewhat 

 lower than on the same date of the preceding year. Samples 

 taken to a depth of 3 feet in the prairie showed that all of the 

 available water had been used. Indeed, at this time, practically 

 all of the vegetation except Hoorebekia racemosa, Solidago mls- 

 souriensis, Carum gairdneri, and a few other serotinal bloomers 

 had dried up. An examination of the root-systems of numerous 

 prairie species shows, however, that many of them obtain water 

 at much greater depths than 3 feet (Figs. 150, i$b, and i$c). In 

 the underlying rocky soil on this butte it is probable that consider- 

 able water was still available at this date. Because of the rocks, I 

 was unable to secure samples at greater depths than 2 feet in the 

 pine community, but these soils on August 13, 1914, were even 

 drier than those in the prairie. Likewise, the deeper soils in the 

 fir-tamarack community were very dry. 



The close similarity in water content between the soils of the 

 prairie and pine communities is just what one might expect when 

 the latter consocies was still quite open and only small amounts 

 of organic matter had been added to the soil. There is a close 

 similarity between these graphs and those obtained at Colfax in 

 communities of about the same stage of development. 



In order to determine the relation between the evaporating 

 power of the air and the water content of the soil in the cedar 

 community as compared with earlier stages in succession, a series 

 of stations was maintained on Cedar Mountain during the sum- 

 mers of 1913 and 1914. A station was maintained in an area of 

 the climax cedar forest which occupied a north slope and a ravine 

 through which flows a small stream. This forest is over 95 per 

 cent, pure cedar, mostly large trees from 2 feet to more than 3 

 feet in diameter. The rest of the trees are large white firs, most 

 of which are dead. The characteristic undergrowth of meso- 

 phytic shrubs and herbs need not be described here. 



About 700 feet beyond the station in the cedars and occupying 

 a slope somewhat above the latter, a station in the fir-tamarack 

 community was maintained. The Douglas fir and tamarack are 



32 



