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.