[61] Bull. Ala. Exp’t Station, No. 96, 1898.
[62] Kosticheff, Formation and Properties of Humus; in abstract Jour. Chem. Soc., 1891, p. 611.
[63] See Merrill, Rocks and Rock weathering.
[64] Shaler (Origin and Nature of Soils; 12th Rept. U. S. Geol. Survey, p. 311) says: “Annual plants cannot in their brief period of growth push their roots more than six to twelve inches below their root-crowns”—a generalization measurably true for the humid region only. According to F. J. Alway, the roots of cereals penetrate to 5-7 feet in Saskatchewan, also.
[65] See “Studien über die natürlichen Humusformen,” by Dr. P. E. Müller.
[66] Excepting only the water-solutions of certain salts, among which common salt, kainit and nitrate of soda are of agricultural interest. Common salt may increase the capillary rise to the extent of more than five per cent.
[67] A heat unit, or “calorie,” is the amount of heat required to raise the temperature of a unit-weight (pound, kilogram, or gram) of water one thermometric degree. According to the unit-weight and thermometric scale used, the figures will vary, but in this text the basis is understood to be kilograms and the centigrade scale.
[68] “Water and Forest,” January, 1905. “The Use of Water,” by S. Fortier.
[69] See Wollny’s experiments, Forsch. Agr. Phys. Vol. 20, p. 58.
[70] It should be understood that it is by no means easy to insure full saturation in any considerable volume of air.