^{page 340 note 1} Hilgard, , Soils, 1918, p. 209.Google Scholar

^{page 340 note 2} U.S. Bur. Plant Indus., Bul. 230, 1912.Google Scholar

^{page 341 note 1} Journ. Agric. Research, 7, 345, 1916.Google Scholar

^{page 341 note 2} Calif. Agric. Expt. Sta., Rpt., 1892–1994, p. 70.Google Scholar

^{page 341 note 3} Journ. Agric. Research, 9, 27, 1917.Google Scholar

^{page 341 note 4} Mem. Dept. Ag. India, Chem, Series, 6, 3, 171, 1921.Google Scholar

^{page 342 note 1} Hardy, F., Journ. Agric. Sci., 13, 243, 1923.CrossRefGoogle Scholar

^{page 342 note 2} Cornell Univ. Ag. Expt. Sta., Mem. 21, p. 497, 1919.Google Scholar

^{page 344 note 1} Journ. Agric Sci., 11, 441, 1921.Google Scholar

^{page 345 note 1} The pore space of the air-dry soils, passed through a 1 mm. sieve, and packed into perforated brass boxes, was found to vary between 55 and 65 per cent. The theoretical pore space for particles of a given diameter in maximum packing is 26 per cent.

^{page 345 note 2} In practice, it is impossible to obtain only film water between the soil particles. Two different definitions for the maximum water retentivity constant have therefore arisen; oertain writers (e.g. Hilgard) define the constant as the quantity of water that a soil can hold when the pore spaces are completely filled with water; others (e.g. Wilsdon), as the quantity of water held when free liquid occurs only as surface films.

^{page 346 note 1} A somewhat similar result was obtained in connection with the determination of shrinkage coefficients (see Table III, column 6). The numerical results obtained are not, of course, comparable with those obtained in the retentivity experiments, since the state of the material on which volume expansion was measured, differed in the two cases. The phenomena of volume expansion of soils, both under natural and artificial conditions, are being further investigated.

^{page 347 note 1} The reader is referred to Ostwald, Wo., Theor. and Applied Colloid Chem., 1917, p. 152Google Scholar, for references to literature on the subject of the structure of humus colloids, and to Bancroft, , Applied Colloid Chem., 1921, p. 76Google Scholar, for an account of the colloid science of cellulose.

^{page 348 note 1} U.S. Bur. Plant Indus., Bul. 230, 1912.Google Scholar

^{page 348 note 2} For a discussion of the significance of the wilting coefficient, see Blackman, , Journ. Ecology, 2, 43, 1914CrossRefGoogle Scholar; also Mason, , West Ind. Bul. 19, 138, 1922Google Scholar. The relationship between this, as well as that of other soil moisture constants, and vapour pressure gradients in soils is fully considered by Thomas, , Soil Science, 11, 409, 1921.CrossRefGoogle Scholar

^{page 348 note 3} West Ind. Bul. 19, 153, 1922.Google Scholar

^{page 348 note 4} Mason, however, considers the divergencies not to be significant.

^{page 349 note 1} Briggs, and McLane, , U.S. Bur Soils, Bul. 45, 1907.Google Scholar

^{page 349 note 2} See Russell, , Soil Conditions and Plant Growth, 1921, pp. 218–27Google Scholar, for a summary of the main facts connected with the water supply of the soil. Also Keen, , Journ. Agric. Sci., 10, 60–64. 1920.CrossRefGoogle Scholar

^{page 349 note 3} U.S. Bur. Plant Indus., Bul. 230, 1912.Google Scholar

^{page 349 note 4} U.S. Bur. Sotls, Bul. 50, p. 50. 1908.Google Scholar

^{page 349 note 5} Ibid. p. 52.

^{page 349 note 6} Davis, (Journ. Ind. Engin. Chem., 6, 1008, 1914)CrossRefGoogle Scholar, has adduced evidence to show that the critical moisture content of a soil is also numerically equal to the minimum waterretaining capacity, i.e. to the moisture content at the upper end of a column of soil that has been allowed to take up moisture by vertical capillarity from a reservoir.