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EARL E. SHERPF 



of moisture in the air where the station is hydrophytic ; and again, 

 the greater amount of atmospheric moisture was due, in many 

 places, not merely to the greater sources of supply (soil moisture 

 or surface water) but to the more difficult' means of escape (be- 

 cause of the tall rank vegetation evoked by hydrophytic condi- 

 tions). It will be noted that the average rate in the outer part 

 of the reed swamp (b) sUghtly exceeded that in the swamp-meadow 

 ,(c). This may be explained easily, however, by the fact that 

 in the swamp meadow the vegetation remained more dense and 

 compact in late summer than in the outer part of the reed swamp, 

 thus retarding evaporation. 



Transeau^ has obtained in a mesophytic forest on Long Island, 

 New York, an average daily evaporation rate of 8.5 cm. This 

 was based upon readings taken during a period of less than one 

 month. More recently, Fuller" has obtained for typical mesophy- 

 tic forest, and based upon readings extending over 155 days, the 

 average daily rate of 8.1 cc. While we are not justified by the 

 data at hand in attempting final comparisons, yet, so far as they 

 go, these data indicate that evaporation is slightly less rapid in 

 the swamp white oak-white ash forest than in climax mesophytic 

 forest. If this indication is sustained by further study, as it 

 undoubtedly will be, it will coincide very exactly with the fact 

 that, in the normal development of mesophytic forest from hydro- 

 phytic formations, Quercus hicolor, Fraxinus americana, F. nigra, 

 etc. are antecedent to trees of the climax mesophytic type {Fagus 

 grandifolia, Acer saccharum, etc.). 



In the autumn of 1911, a study of evaporation at different 

 levels above the soil surface was made. Beginning September 

 3, weekly readings were taken with four atmometers arranged 

 at different heights in a dense growth of Phragmites communis, 

 and with three more atmometers added to the one already at 

 station 1, among Typha. The last readings were taken on Octo- 

 ber 22. After correction to correspond with the readings of a 



' Transeau, E. N., The relation of plant societies to evaporation. Bot. Gaz. 

 46 : 217-231. 1908. 



'Fuller, G. D., Evaporation and plant succession. Bot. Gaz. 62: 193-208. 

 1911. 



