CHAPTER IX. SOIL AND SUBSOIL (_continued_), 142.—ORGANISMS INFLUENCING SOIL-CONDITIONS. BACTERIA, 142.—_Micro-organisms of the Soil._ Bacteria, Moulds, Ferments, 142.—Numbers at Various Depths, given by Early Observers, 142.—Investigations of Hohl; Mayo and Kinsley. Tables, 143.—Multiplication of the Bacteria, 144.—Aerobic and Anaerobic Bacteria, 144.—Food Materials required, 145.—Functions of the Bacteria, 145.—Nitrifying Bacteria. Figures, 146.—Conditions of their Activity. Table, 146.—Effects of Aeration and Reduction, 147.—Unhumified Organic Matter does not Nitrify, 148.—Unhumified Vegetable Matter, Functions in Soils, 148.—Denitrifying Bacteria. Figures, 148.—Ammonia-forming Bacteria. Figures, 149.—Alinit, 149.—Effects of Bacterial Life on Physical Soil Conditions, 149.—Root-bacteria, or Rhizobia of Legumes, 150.—Figures of Root Excrescences and Corresponding Bacteroids, 152.—Varieties of Forms, 154.—Mode of Infection, 154.—Cultural Results, 155.—Table Showing Increased Production by Soil Inoculation, 155.—Other Nitrogen-absorbing Bacteria, 156.—Distribution of Humus in the Surface Soil, 157.—Fungi, Moulds and Algae, 157.—_Animal Agencies_—Earthworms, Insects, Burrowing Quadrupeds, 158. 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.