EVAPORATION AT SKOKIE MARSH 



159 



standard atmometer cup, the data were plotted graphically. 

 Among Phragmites (fig. 3). the average daily evaporation for the 

 seven weeks, at 0 cm. (the soil surface), was 2.5 cc; at 25 cm., 

 4 cc. ; at 107 cm., 5.3 cc. ; at 198 cm., in the uppermost atmospheric 

 stratum among the Phragmites plants, 7.5 cc, — or just 300 % as 

 great as at the soil surface. Among Typha (fig. 4),^ the average 

 daily evaporation for the seven weeks, at 0 cm., was .64 cc; at 



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Fig. 3 



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Fig. 4 



Fig. 3. Average daily evaporation rates among Phragmites communis, at 

 a, 0 cm.; b, 25 cm.; c, 107 cm., and d, 198 cm. 



Fig. 4. Average daily evaporation rates among Typha lalifolia, at a, 

 0 cm.; b, 25 cm.; c, 107 cm., and d, 175 cm. 



' Because of the faulty working of the atmometer at 0 cm., the results for the 

 first two and the last weeks are not plotted, and the average here given (0.64 cc.) 

 is for the remaining four weeks. Enough certain data were obtained, however, 

 for the other three weeks to show that the total average would have been even 

 less than 0.64 cc. 



