73 



and McNutt ('14), SherfT ('12, '13a, '13b), and Gleason and Gates 

 ('12). Shelf ord ('12, '13a, '13b, '14a), utilizing the evaporation 

 data of the plant ecologists, has applied the same to animal associa- 

 tions also, and he has further tested some of these ideas experiment- 

 ally in the laboratory. In Ohio, Dachnowski ('11) and Dickey ('09) 

 have made records of data obtained by the use of the porous cup, and 

 in Iowa Shimek ('10, '11) has used the open-pan method. Mention 

 should also be made of Yapp's observations ('09) on a marsh in Eng- 

 land. A very important summary of evaporation records, in the open 

 and in forests, is given by Harrington ('93). The effect of wind- 

 breaks upon evaporation has been studied by Bates ('n) and Card 

 ('97). Finally, mention should be made of Hesselman's studies of 

 relative humidity in forest glades in Sweden ('04). 



Our records from the Charleston region will be given first, and then 

 their significance will be discussed. The unglazed porcelain cups, with 

 a water reservoir, were placed so that the tops of the cups were about 

 six inches above the soil in the habitats examined, and at weekly in- 

 tervals the water loss was measured. The instruments were in opera- 

 tion simultaneously, so that the results are comparable. The standard 

 instrument was located in the open exposed garden of the Eastern 

 Illinois Normal School at Charleston, which was considered as unity, 

 or 100 per cent. For further details as to the conditions where the 

 atmometers were located consult the description of the stations and 

 the photographs. 



An examination of the diagram (Fig. 2) will show that although 

 based upon a limited amount of data (for less than a month, from 



Intensity of evaporation. 



Standard, open garden, Normal School 

 Sta. Ill, b. Mixed prairie and young forest 

 Sta. II, a. Grassy area, Panicum 

 Sta. II, a. Grassy area, Euphorbia 

 Sta. IV, a. Upland, open woods 

 Sta. Ill, a. Silphium on black soil 

 Sta. II, a. Colony of S. laciniatum 

 Sta. IV, b. Ravine slope, open woods 

 Sta. IV, c. Dense climax forest cover 



Fig. 2. Diagram of the relative evaporation in different prairie and forest 

 habitats, showing the great reduction in evaporation with the development of a closed 

 forest canopy of a climax forest; Charleston, Illinois. 



