SEVENTH ANNUAL MEETING 61 



basis. Throughout the season readings were taken once each 

 week and the results reduced to the average daily loss for each 

 week. The accompanying graphs have been made with the 

 average daily loss in cubic centimeters as ordinates and with 

 weekly intervals as abscissae. 



In the beech-maple forest three stations were established in 

 representative positions. During this season the herbaceous 

 vegetation was somewhat sparse and therefore probably modi- 

 fied conditions from time to time but little. One of these sta- 

 tions was placed on the crest of a low ridge which gave it some- 

 what more exposure to the wind. In figure 1, this station, 

 represented by the heavy line, has a rather higher evaporation 

 rate altho it is fairly parallel with the other two stations. Three 

 stations were established in the wheat field, which had also been 

 sown with clover, with more or less uniform exposure. One of 

 these stations was surrounded by taller wheat and more vig- 

 orous clover, which produced a luxuriant crop after the wheat 

 had been harvested. In figure 2, this station, represented by 

 the heavy line, has a slightly lower evaporation rate. Three 

 stations of uniform exposure were established in the oat field 

 about June 8th, which gave fairly parallel curves. The aver- 

 age of these curves is plotted in figure 3 (c). No records were 

 taken after the oats were harvested early in August. 



II. Soil Moisture : Through the work of Briggs and 

 Schantz 3 and others the wilting coefficient has been established 

 as a more or less satisfactory standard for the comparison of 

 available growth water for plants in various soils. It repre- 

 sents the water content above which the growth takes place, 

 and is expressed in percentage of dry weight of the soil. 



In the determination of the soil moisture in the habitats 

 studied, weekly samples of soil were taken from representative 

 stations at depths of 7.5 cm. and at 25 cm. below the surface. 

 This soil was brought to the laboratory in closed jars where it 

 was weighed and dried at a temperature of about 104 degrees 

 C, until it reached a constant weight and a percentage of water 

 was calculated on the basis of this dry weight. The wilting 

 coefficient of the same soils were obtained by the wax seal 

 method of Briggs and Schantz, 3 and also by the indirect cen- 

 trifuge method of the same workers. In figures 4 and 5 

 graphs have been plotted representing the range of soil mois- 

 ture on the ordinates and the weekly readings on the ab- 

 scissae. Upon these same diagrams the wilting coefficients 

 have been represented in dotted lines. The available growth 

 water is therefore represented by the intervals between soil 

 moisture and wilting coefficient. 



