74 



August 19 to September 22) the facts are in harmony with similar 

 studies elsewhere covering a much longer period, so that there is valid 

 reason for confidence in them. The standard instrument was located, 

 as already mentioned, in an open, exposed cultivated garden, where the 

 intensity of evaporation was very high. The black soil prairie areas, 

 Stations II and III, a, have an average of 56.1 per cent. — a condition 

 much like that in the grassy-Euphorbia prairie at Loxa (Station II, a) 

 — or a little more than half that of the standard instrument. The dry 

 upland area of mixed prairie and young forest, on gray silt loam ( Sta- 

 tion III, b), has an intensity of 80 per cent. This is in the region of 

 the most extensive grassy prairie about Charleston; the general ap- 

 pearance of the region is shown in Plate XIII. A surprising feature 

 of the table is the evaporation in the open-crowned upland oak-hickory 

 woods (Station IV, a). In this forest perhaps two thirds to three 

 fourths of the ground was shaded, and it was very well drained. The 

 evaporation here reached 54.2 per cent., being very near that of the 

 average of the black soil prairie (56.1 per cent.). I had anticipated 

 much less evaporation than on the prairie, a position more intermedi- 

 ate between the prairie and the lowland forest, or about 42 per cent, 

 (cf. Harvey, '14:95). The ravine slope (Station IV, b), although 

 somewhat open, has 31.5 per cent. — a very low rate of evaporation — 

 and is remarkably close to that of the densely crowned lowland for- 

 est (Station IV, c), at 26.9 per cent. The decline, however, in the 

 intensity of evaporation with the degree of completeness of the for- 



Per cent, of standard 



Sta. 11. Salt marsh outer margin 



Sta. 3. Gravel slide, open 



Sta. 1. Carnegie garden, standard 



Sta. 9 and 10. Upper beach 



Sta. 12. Salt marsh, inner margin 



Sta. 2. Garden, high level 



Sta. 4. Gravel slide, partly invaded 



Sta. 5. Forest, open 



Sta. 13. Fresh-water marsh 



Sta. 6. Forest, typical mesophytic 



Sta. 7. Forest, ravine type 



Sta. 8. Forest swamp type 



Fig. 3. Diagram of the relative intensity of evaporation in the lowest stratum 

 of different kinds of habitats, Long Island, N. Y. (After Transeau.) 



