480 BOTANICAL GAZETTE [JUNE 
ard, remained in its original location. Readings in the field were 
continued for 23 days, and then all the instruments were again 
standardized for 93 hours in the original location. Readings of 
the standard were taken daily, while those in the field were read at 
intervals of one to four days. Since the purpose of the work called 
for the total amount of evaporation rather than the daily fluctua- 
tions, the observed amounts of evaporation from each instrument 
were added, and the total amounts reduced to terms of the standard 
instrument by multiplying by the factor obtained in the two 
standardizations. The results are therefore directly comparable, 
and have been plotted in the accompanying diagram (fig. 6). Since 
they are not absolute values, they have been expressed in terms of 
the evaporation from the standard instrument, which is here desig- 
nated 1.00. 
Two atmometers were located in each of five distinct associa- 
tions, and one other was set up on the sandy beach of Quiver Lake. 
Four of the associations were in sandy soil, and their vegetation 
has been described in detail by GiEAson.4 A brief description of 
the vegetation and the successional relations of the associations, 
however, may be given here. 
The standard.—During standardization the atmometers were 
placed on the ground in the Chautauqua Park athletic field, and the 
standard instrument was kept there during the whole period of 
observation. This field was formed by leveling the sandy ground 
after cutting off the mixed forest association which covered it. It 
was bordered by a cultivated field on the east, and was surrounded 
on the other three sides by forest at a distance of 50-100 m. from 
the atmometers. The field was partly covered by weeds, of which 
the following were the most abundant: Erigeron canadensis, 
Mollugo verticillata, Eragrostis Purshii, Erigeron divaricatus, 
Verbena stricta, Erigeron annuus, Cenchrus carolinianus, and a few 
other grasses. The atmometers were placed in the center of an area 
cleared of the taller weeds for a radius of about one meter (fig. 1). 
The river bank.—One atmometer was maintained on the sandy 
eastern bank of Quiver Lake, at a height which corresponds to a 
4Gueason, H. A., The vegetation of the inland sand deposits of Illinois. Bull. 
Til. State Lab. Nat. Hist. 9: 23-174. figs. 6. pls. 20. 1910. 
