INDEX. 



579 



Nitrification and denitrification 145 



in alkali lands 68 



in soil of " ten-acre tract." 359 



intensity in arid climates, 68 



list of substances favoring 147 



of organic matter in soils, experiments 358 



not active in unhumified matter 359, 360 



Nitrifying Bacteria 146 



Nitrobacterinm ; conditions of activity 146 



Nitrogen-absorbing bacteria 156 



Nitrogen, absorbed more abundantly than oxygen 278 



accumulation of, in humus 1 24 



adequacy in humus, lowest limit of 363 



in soils 357 



availability of, in soils ; ascertainable 363 



content of humus 135 



deficiency, pot test, figure 362 



determination of, in soils 357 



hungry soils ; table 361 



percentages in humus, what are adequate 360 



supply of plants, views on, 150 



Nitrosomonas, figure 246 



Nodules of legumes 151 



North Central States, herbaceous vegetation on calcareous soils ... .514, 515 



lowland growth in uplands, when 515 



vegetation and soil-character 513 



Nutritive salts in alkali 44 1 



O. 



Ocean currents, Gulf-stream and Japan-stream 295 296 



Olive, resistance to alkali 47>S 



Organic and organized constituents of soils 1 20 



Organisms influencing soil-conditions 142 



Oxalic acid, secretion by lichens 19 



Oxidation, expansion by iS 



Oxids constituting earth's crust ; table 31 



Oxygen, action in weathering rocks iS 



proportion of, in earth's crust 30 



Pamperos 9 



Peat bogs 122 



Peaty soil, shrinkage 1 1 7 



Percolation in natural soils : diagram 223, 225, 226 



rate of, as influenced by grain-sizes 224 



Permanent value of land vs. Immediate productiveness 340 



