CHAPTER XI.

THE WATER OF SOILS. HYGROSCOPIC AND CAPILLARY MOISTURE, 188.—General Properties, 188.—Physical Factors of Water compared with other Substances. Table, 188.—Capillarity or Surface Tension, 189.—Heat Relations, 190.—Density, 190.—Specific Heat and its Effects, 190. Ice, 191.—Vaporization, 191.—Solvent Power, 191.—Water-requirements of Growing Plants, 192.—Evaporation from Plants in Different Climates, 192.—Relations between Evaporation and Plant Growth. Table, 193.—Fortier’s Experiments. Figure, 194.—Different Conditions of Soil Water, 196.—_Hygroscopic Water in Soils; Table_, 196.—Influence of Temperature and Air-Saturation, 197.—Utility of Hygroscopic Water to Plant Growth, 199.—Mayer’s Experiments, 200.—Summary, 200.—_Capillary Water_, 201.—Ascent of Water in Soil-Columns. Table, 202.—Ascent in Uniform Sediments. Figure, 204.—Maximum and Minimum Water-holding Power, 207.—Capillary Water held at different Heights in a Soil Column. Table, 208.—Capillary Action in Moist Soils, 210.—Proportion of Soil Moisture Available to Plants, 211.—Moisture Requirements of Crops in the Arid Region, 211.—Tables of Observations in California, 214.