ror1| DACHNOWSKI—CRANBERRY ISLAND I4I 
appropriate to the peculiar conditions. To measure evaporation 
in a few places in this locality, and then to assign the results to 
the region as a whole, is a procedure not without its accompany- 
ing shortcomings. It was intended to overcome this difficulty 
partially by measuring the variation in evaporation of the vertical 
as well as the horizontal vapor pressure gradient in a larger number 
of stations, plotting the results, and drawing isothymes. By a 
summation of the evaporation, that of the whole area could be 
calculated with greater accuracy. The distance of Buckeye Lake 
from Columbus and the inconveniences as to available time have 
made it difficult to secure the required observations. However, 
the problem here dealt with does not concern itself with the devel- 
opment of a formulated expression of evaporation for this region. 
The purpose at present is to obtain quantitative data on the rate 
of evaporation, and thus to secure direct evidence as to the rela- 
tion of the observed evaporating power of the air and the nature 
of the vegetation. The more detailed study of the phenomenon 
as originally outlined is now in progress. 
The ordinary markets are not prepared to supply the well 
designed standardized self-registering instruments which have 
been devised to meet the needs of the Weather Bureau (26). 
For ecological purposes, an instrument is required which can be 
placed under conditions practically identical with those which 
the plants themselves endure. For this purpose a small atmome- 
ter partly buried in the soil is desirable. Dr. Forrest SHREVE 
of the Carnegie Desert Laboratory, Tucson, Arizona, courteously 
left at the disposal of the writer several porous cups of the type 
as described and used by Livincston (21). The instruments 
had been previously standardized with an atmometer at Tucson, 
and since they are similar to those sent out from the Desert 
Laboratory to various other stations in the United States, the 
readings obtained may be readily compared. There are certain 
objections to the porous cups as an instrument in the field study 
of habitat conditions. The inability of the cup to withstand 
frost makes it practically impossible to obtain readings for more 
than the growing period of seven months, and the fact that the 
instrument does not prevent the direct entrance of rain to the jar 
