202 BOTANICAL GAZETTE [SEPTEMBER 
the season. Of the 3 stations in the beech-maple forest, no. 11 
was in an area dominated by the sugar maple and well surrounded 
by maple seedlings. No. 11 was near a large beech tree on a slope 
covered with Asplenium angustifolium and Impatiens biflora, while 
no. 13 was in the midst of beech seedlings between two large trees 
of the same species. Together they seemed to represent the aver- 
age conditions in a beech-maple forest. The resulting graphs 
(fig. 3) are very similar, showing coincident maxima and minima 
differing but little in amount. The maxima are in July and 
August, and amount to little more than 12 cc. daily; the minimum 
occurs in September and is scarcely 3 cc. per day. The average 
rate of evaporation at the 3 stations for the 155 days is 8.1 cc. 
per day. 
It is here interesting to note the close correspondence between 
the records for this beech-maple forest and those obtained by 
TRANSEAU (8) in a mesophytic forest containing a small percentage 
of beech and situated on Long Island, N.Y., where for the period 
of observation from June 5 to July 2, 1907, the evaporation rate 
averaged 8.5 cm. daily, compared with 8.4 cm. daily during the 
month of June, 1910, in the Otis, Ind., forest. While it is not safe 
to draw any very definite conclusions from records covering but 
a single month, it may be assumed that the two associations differ 
very little in the amount of mesophytism developed. 
Several methods may be employed in comparing the data 
obtained from the various evaporation stations. Perhaps the best 
is to plot upon the same chart graphs representing the mean daily 
evaporation by weeks, from the several stations in the different 
associations (fig. 4). It will be seen that the graphs show several 
similarities, but more differences. The maxima and minima are 
generally coincident in time and proportionate in amount. All 
show great irregularity during spring and autumn, and a compara- 
tively high rate during July and August. The general height of 
the different graphs probably gives the most instructive and 
interesting differences in the various habitats. That of the 
cettonwood dune is farthest removed from those of the other asso- 
ciations, and shows a habitat not only with great evaporating 
power, but one of great extremes, the difference in rate between 
