1912] SHERFF—SKOKIE MARSH 421 
From September 3 to October 22, 1911, weekly readings were 
taken of the rates of evaporation at different levels above the soil 
surface. Among the plants of Phragmites, four atmometers were 
placed at levels ranging from o m. to 1.95 m. above the soil. The 
average daily rate for the seven weeks at 1.95 m., or near the top 
of the Phragmites plants, was found to be 7.5 cc., just three times 
as great as the average daily rate of 2.5 cc., at the surface of the 
soil. Similar results were obtained with five atmometers in a 
dense growth of Typha. In each case the data secured are found to 
support YApp’s important contention (20) that for species growing 
side by side, but vegetating mainly at different heights, the condi- 
tions of growth may be very unlike. 
The depth of the water table in the reed swamp and the swamp 
meadow was observed each week from May 21 to October 22, 1911. 
The water in Skokie Stream was about 1 m. deep in May; its depth 
then gradually decreased until in July, when the stream bed was in 
most places fairly dry; in August the water began to rise again, 
and by October had reached an average depth of about 1.1 m. 
In the rest of the reed swamp and in the swamp meadow the 
water table during May was coincident with or above the soil 
surface; in early September it sank to the maximum depth of 1 m. 
in the reed swamp and 1.75 m. in the swamp meadow; and then, 
rising rapidly, reached the surface again by the middle of October. 
According to farmers in the vicinity of Glencoe, Skokie Stream 
has sometimes in the past risen until a depth of about 3m. was 
reached; in such cases the entire marsh was of course deeply 
submerged. Various attempts have been made to classify the 
constituent species of a formation with relation to the optimum 
water table depth for each species. But where the water table 
varies greatly in depth from month to month and from year to 
year, data must be secured through many years if they are to show 
more than merely the relative degrees of hydrophytism to which 
plants in different places are subject. 
Litmus tests each week, from May 21 to October 22, 1911, showed 
the water in Skokie Stream to be either neutral or slightly alkaline. 
Similar tests showed the soil water in the outer parts of the reed 
swamp and in the swamp meadow to be usually neutral or slightly 
