RELATION BETWEEN EVAPORATION AND PLANT SUCCESSION 1 67 
A similar series of experiments was run in connection with the 
estabhshment of pine plants in the aspen association. Pine seeds are 
furnished by large trees bordering the lake and scattered sparingly in 
the main body of the pine land. The ground conditions are various. 
Open sandy soil may be quite plantless where fire damage has been 
very severe. The ground is sometimes covered with a dense carpet 
of moss or sod, which makes seeding ineffective. 
Fig. 5. Margin of hardwoods, the result of clean cut lumbering. July 14, 1916. 
Eleven atmometers were set out on a line running back from the 
lake near the Biological Station under conditions as follows: No. 20 
in an open growth of aspen, the ground covered with Pteris; No. 18 
near the preceding in a growth of Pteris under the open sky; No. 26 
at the foot of a slope in a dense aspen thicket, in which the ground was 
entirely obscured by the luxuriant growth of Pteris; No. 21 about 20 
meters from the preceding at the crest of a slope where the ground 
flora was predominantly formed by GauUheria procumhens under a 
fairly open aspen thicket (Fig. 8). Atmometers No. 24 and No. 25 
were run in a dense aspen thicket, where Pteris was also luxuriant. 
This thicket was separated from the uplands by a steep partially 
cleared slope about 10 meters high. Atmometers No. 17 and No. 19 
were run on this slope. On the uplands there were fewer pine seed- 
lings, both because of the distance from seed trees and the greater 
