CHAPTER X.

SOIL AND SUBSOIL IN THEIR RELATIONS TO VEGETATION, 161.—Physical Effects of the Percolation of Surface Waters, 161.—Chemical Effects; Calcareous Subsoils and Hardpans, 161.—“Rawness” of Subsoils in Humid Climates, 162.—Subsoils in the Arid Region, 163.—Deep Plowing and Subsoiling in the Arid Region; examples of Plant growth on Subsoils, 164.—Resistance to Drought, 167.—Root System in the Humid Region, 168.—Figures of the Root System of an Eastern (Wisconsin) Fruit Tree, 168.—_Comparison of Root Development in the Arid and Humid Regions_, 169.—Prune on Peach Root, 169.—Adaptation of Humid Species to Arid Conditions, 169.—Grapes, 170.—Kentucky and California Maize, 175, 176.—Hops, 172.—Deep-Rooting in the Arid Region, 174.—Goose Foot and Figwort, 174.—_Importance of Proper Substrata in the Arid Region_, 173.—Injury from Impervious Substrata. Figure, 177.—Faulty Lands of California. Figure, 178.—Shattering of Dense Substrata by Dynamite, 181.—Leachy Substrata, 182.—“Going-back” of Orchards, 182.—Hardpan, Formation and Varieties, 183.—Nature of the Hardpan Cements, 184.—Bog Ore, Moorbedpan and Ortstein; Calcareous and Alkali Hardpan, 184.—The Causes of Hardpan, 185.—“Plowsole,” 186.—Marly Substrata, 186.