RESEARCH METHODS IX STUDY OF FOREST ENVIRONMENT. 207 
106. Bouyoucos, G. J., and McCool, M. M. The freezing-point method as a new 
means of measuring the concentration of the soil solution directly 
in the soil. Mich. Agr. Exp. Station, Tech. Bull. 24, 1915. 
107. . . Further studies on the freezing-point lowering of soils. 
Mich. Agr. Exp. Station, Tech. Bull. 31, 1916. 
108. . The freezing-point method as a new means of determining the 
nature of acidity and lime requirements of soils. Mich. Agr. Exp. 
Station Tech. Bull. 27, 1916. 
109. . Measurement of inactive, or unfree, moisture in the soil by means 
of the dilatometer method. U. S. Dept. Agr., Jour. Agr. Research, 
VIII, 6, Feb., 1917. 
110. Beiggs, L. J. The mechanics of soil moisture. U. S. Dept. Agr., Bu. of 
Soils, Bull. No. 10, 1897. 
111. Briggs, L. J. Electrical instruments for determining the moisture, tem- 
perature, and soluble salt content of soils. U. S. Dept. Agr., Bu. 
of Soils, Bull. 15, 1899. 
112. . Martin, F. O., and Pearce, J. R. The centrifugal method of 
mechanical soil analysis. U. S. Dept. Agr., Bur. of Soils, Bull. 24, 
1904. 
113. and McLane, J. W. The moisture equivalents of soils. U. S. Dept. 
Agr., Bur. of Soils, Bull. 45, 1907. 
114. and Shantz, H. L. The wilting coefficient for different plants and 
its indirect determination. U. S. Dept. Agr., Bur. of Plant Indus- 
try, Bull. 230, 1912. 
115. Buckingham, E. Contributions to our knowledge of the aeration of soils. 
U. S. Dept. Agr., Bur. of Soils, Bull. 25, 1904. 
116. . Studies on the movement of soil moisture. U. S. Dept. Agr., Bur. 
of Soils, Bull. No. 38, 1907. 
117. Cameron, F. K., and Gallagher, F. E. Moisture content and physical con- 
ditions of soils. U. S. Dept. Agr., Bur. of Soils, Bull. 50, 1908. 
118. Chemistry, Bureau of. Official and provisional methods of analysis. 
U. S. Dept. Agr., Bull. 107. 
119. Dixon, H. EL, and Atkins, W. R. G. Osmotic pressures in plants. I. 
Method of extracting sap from plant organs. Sci. Proc. Royal 
Dublin Soc, n. s. 13, pp. 422-33, 1913. 
120. Fletcher, C. C, and Bryan, H. Modification of the method of mechanical 
soil analysis. U. S. Dept. Agr., Bur. of Soils, Bull. 84, 1912. 
121. Free, E. E. Studies in soil physics, The Plant World, v. 14, Nos. 2, 3, 5, 7, 
and 8, 1911. 
122. Grandeau, Louis. Traite' d'Analyse des Matieres agricoles, Paris, 1877. 
123. Harris, J. A., Lawrence, J. V., and Gortner, R. A. The cryoscopic con- 
stants of expressed vegetable saps as related to local environmental 
conditions in the Arizona deserts. Phy. Res., vol. 2, No. 1, 1916. 
124. Hartley, Carl. The control of damping-off of coniferous seedlings. Bur. 
Plant Ind., U. S. Dept. Agr. Bull. 453, 1917. 
125. Hilgard, E. W. Soils. New York, 1906. 
126. Hibbard, R. P., and Harrington, O. E. Depression of the freezing-point 
in triturated plant tissues and the magnitude of this depression as 
related to soil moisture. Phys. Res., vol. I, No. 10, 1916. 
127. Hoagland, D. F. The freezing-point method as an index of variations in 
the soil solution due to season and crop growth. U. S. Dept. Agr., 
Jour. Agr. Res., XII, 6, Febr. 11, 1918. 
128. Jones, H. C. Physical chemistry. 4th ed., 1918. New York. 
