482 BOTANICAL GAZETTE [JUNE 
Drainage Canal. The evaporation from this atmometer was very 
pronounced during the day, but was much lower at night. Some- 
times virtually no nocturnal evaporation was indicated, while on 
the athletic field, about 200 m. inland and separated from the river 
by a forested dune, the evaporation was quite noticeable. 
The bottom-lands.—The bottom-lands immediately across the 
river show plainly the results of the persistent high water during 
the last few years. The low banks and islands between the numer- 
ous lakes are still mostly covered with trees, but they are gradually 
being killed. A marginal zone of Salix longifolia represents the 
Salix-Cephalanthus association, while in the interior or highest 
parts of the islands a few maples, Acer saccharinum, occur, showing 
the former presence of the Ulmus-Acer association. A few pecan 
trees, Carya illinoensis, are present, but other tree species are rare. 
The ground is submerged during the greater part of the year. If 
emergence occurs during the summer, the surface is in a few weeks 
thickly covered with a growth of weeds, of which the most abundant 
are Xanthium commune, species of Aster, and other composites, and 
with numerous seedlings of willow and maple, none of which, 
however, survives the following winter. One atmometer was 
placed in a large rotten willow stump, about 6 m. from the river 
bank and about 2 m. above the surface of the mud. When first 
located, the station was covered half a meter deep with water. 
Another instrument was stationed in a maple stump, 1.7 m. above 
the mud, and about 8 m. from the river (fig. 2). Since the maple 
leaves were more nearly confined to the upper parts of the trees, 
while the willows were leafy almost to the ground, the better circu- 
lation of air permitted a greater evaporation under the maple 
trees. 
The bunch-grass association.—Of the several consocies of the 
bunch-grass association occurring in the region, two adjacent ones 
were selected, characterized respectively by Eragrostis trichodes and 
Leptoloma cognatum. ‘The former of these is the more stable, and 
consists chiefly of well defined bunches of Eragrostis spaced about 
2-4 dm. apart. Other less conspicuous or less abundant grasses 
occur also, particularly Andropogon furcatus, Leptoloma cognatum, 
Sorghastrum nutans, and Paspalum setaceum, with a few plants of 
