1914] FULLER— EVAPORATION AND SOIL MOISTURE 195 



made in this 



may 



data for these associations upon a sandy soil. In addition to this 

 successional series of associations, through the cooperation of 

 some of the writer's students, data were obtained from the edanhic 



Chicago 



from May 



October 31 (178 days); during 191 1, from May 

 (180 days) ; and during 19 12, from May 3 to October 22 (172 days), 

 the records for the oak-hickory forest and the edaphic prairie 

 being for the seasons of 19 n and 19 12 only. Weekly visits were 

 made to all stations throughout this period, except to those of the 

 beech-maple forest, which were visited once in two weeks. A 

 preliminary report of much of the data obtained during the first 

 season has already appeared. 1 



INSTRUMENTS AND METHODS 



The instruments employed were mostly the porous cup atmom- 

 eter devised by Livingston, although during the first season a 

 few of the type described by Transeau (3) were also used. The 

 atmometers were mounted in wide-mouthed bottles, having a 

 capacity of 500 cc, closed with tightly fitting cork stoppers that 

 were perforated for the atmometer tubes and for bent capillary glass 

 tubes which served to equalize the atmospheric pressure within 

 the bottles with that of the exterior air, without causing any loss 

 by evaporation or permitting rainwater to enter the reservoir. 

 The bottles were sunk in the soil about two-thirds of their height, 

 so that the evaporating surface of the instruments was 25-20 cm. 

 above the surface of the soil. Except where otherwise specified, 

 the readings were made weekly by filling the bottles from a gradu- 

 ated burette to a file scratch on the neck. The small area of the 

 water surface at this point made the probable error in readings less 

 than 0.5 cc, and this could have had no appreciable effect upon the 

 results. The instruments were all standardized to the same unit 

 before being used, restandardized at intervals of 6-8 weeks during 

 the season, a revolving table being used for the purpose similar to 



1 Bot. Gaz. 52:193-208. 191 1. 



