INDEX OF SUBJECTS 



881 



History of soil microbiology, 834 



Hodotermes, 363 



Hog peanut, nodule bacteria of, 137 



Holophrya, 335 



Holotricha, 335 



Holozoio protozoa, 315 



Hoplolaimus, 348 



Hormodendrum, 265 



Humic acids in soil, 671, 696-697, 



698-699 

 Humid soils, distribution of bacteria 



in, 34 

 Humification, 695 

 Humin, 697, 698 

 Humus compounds, chemistry of and 



classification, 671, 696-699 

 Humus, decomposition of, 151, 298, 



310, 449 

 formation of, in soil, 309, 447, 460, 



681, 689-691, 692-696 

 influence of, on nitrogen fixation, 580 

 nature of, 691-696, 707 

 role of, in soil processes, 629 

 Hyalopus, 253 

 Hyalosphenia, 332 

 Hyalotheca, 229 

 Hydrocarbons, decomposition of, by 



bacteria, 159, 204, 465 

 Hydrogen bacteria, 59, 403 

 Hydrogen, energy utilization in the 



oxidation of, 403 

 Hydrogen formation, by bacteria, 177 

 in the decomposition of cellulose by 



bacteria, 193, 437, 440 

 Hydrogen oxidation by bacteria, 98, 99, 



188 

 Hydrogen-ion concentration (see Re- 

 action) 

 Hydrogen peroxide, decomposition of 



in soil, 734 

 Hydrogen sulfide formation, in the 



decomposition of organic matter, 



612, 613 

 in the reduction of sulfates, 602 

 Hydrogen sulfide, oxidation of, 78, 605 

 Hydrogenomonas, 99, 188, 403 

 Hydrolytic decomposition of proteins, 



473, 481 



Hydroxylamine, 526 

 Hymenomycetes, 257, 275, 276, 278, 459 

 Hymenoptera, 356, 357, 358 

 Hymetomelanic acid, 671, 698 

 Hypheothrix, 226 



Hyphomycetes, 3, 250, 252, 265, 276, 289 

 Hypochnus, 278 

 Hypolricha, 336 

 Hypoxanthine in soil, 479, 671 



Ichneumonidae, 361 

 Immunity theory and nodule forma- 

 tion, 128, 589 

 Incubation of plates, 23 

 India-ink method of isolating bacteria, 



55, 101 

 Indigo-carmin as reducing agent, 170 

 Infusoria, 314, 335 

 Inoculation, cross, of nodule bacteria, 



136 

 Inoculation of soil with non-symbiotic 



bacteria, 105 

 Inoculation, principles of, 817-833 

 Insects in soil, 3, 50, 342, 356, 359 

 Insecticides, 362 

 Interpretation of results of plate 



counts, 24-27 

 Inulin, decomposition of, 462 

 Invertebrate fauna of soil, causing 

 plant and animal diseases, 810 

 economic importance of, 360 

 occurrence of, 341-363 

 role of, in soil, 360 

 Invigoration of nitrogen-fixing bac- 

 teria, 111 

 Iota, 349 



Iron, as a catalytic agent, 540 

 as a reducing agent, 170 

 accumulation by bacteria, 94 

 bacteria, 59, 92-96, 402-403 

 compounds, energy utilization in the 



oxidation of, 402 

 influence of, on the growth of Azoto- 



bacter, 578 

 precipitation of, 402 

 transformation of, in soil, 666 

 Ironus, 348, 349 



