75 



est crown, is strikingly shown in passing from the open upland 

 woods, at 54.2 per cent, to the ravine slope at 31.5 per cent, and on 

 to the lowland forest at 26.9 per cent. 



A comparison of these results with those secured by Transeau 

 ('08) on Long Island, is instructive. His standard instrument was 

 also in an open garden (Fig. 3), comparable with the Charleston 

 standard. A gravel slide, partly invaded by plants, had an ev?iporation 

 of 60 per cent., comparable with the open prairie at Charleston; the 

 open forest, 50 per cent., comparable with the upland open Bates 

 woods at 54.2 per cent. ; and the mesophytic forest, 33 per cent., com- 

 parable with the ravine and lowland places in the Bates woods at 31.5 

 and 26.9 per cent, respectively. 



Fig. 4. Eelative intensity of evaporation in different kinds of habitats on sandy 

 soil, Havana, Illinois. (After Gleason and Gates.) 



Another series of relative evaporation observations was made by 

 Gleason and Gates ('12) on sandy soils at Havana, Illinois. As their 

 methods were similar to those used at Charleston, useful comparisons 

 may again be made. The standard instrument was in an open area 

 comparable to the garden at Charleston. An examination of Figure 4, 

 summarizing the results of their study, shows that upon the grass- 

 covered sand prairie (bunch-grass) the evaporation was about no per 

 cent., that in open black oak (Q. velutina) woods (on sand) it was 

 about 60 per cent., and that in a denser hickory-black-oak-hackberry 

 mixed forest (somewhat open) it was about 31 per cent. There is thus 

 a close general correspondence between the conditions at Havana and 

 Charleston, although the evaporation upon sand prairie appears to be 

 relatively much greater than upon the black-soil prairie. 



Fuller ('11) and McNutt and Fuller ('12) have made comparative 

 studies in different kinds of forest in northern Illinois and in northern 



