121;
in surface-soil, 121;
in swine-urine, 230;
in woollen rags, 427.

Nitrogenous guano, 300-308, 329.

Nitrogenous manures, application of, 478;
benefit cereals, 494;
hurtful to leguminous crops, 523.

Nitrogenous organic substances, in Chincha guano, 305;
in concretionary nodules, 328.

_Nitrosomonas_, 167.

Nitrous acid, converted into nitric acid, 168;
formed from ammonia, 167.

Nobbe, on fixation of free nitrogen, 136;
on potash in soil, 108.

Noellner on origin of nitrate-fields, 339.

Norfolk, coprolites from, 374;
experiments on barley, 497
--on meadow-land, 509
--on turnips, 513.

North America, guano from, 298, 328.

Norwegian apatite, 375.

Oak-tree, water transpired by, 71.

Oat-straw, composition of, 238;
manurial constituents in, 282.

Oats, Arendt's experiments with, 503;
avenine in, 503;
fertilising ingredients removed from soil by, 485;
hardy crop, 502;
manurial constituents in, 282;
manuring of, 501-504;
nitrogen removed in crop of, 148;
require mixed nitrogenous manures, 502;
source of nitrogen, 153;
Rothamsted experiments on growth of, 567.

_Oficinas_, 342.

Ohlendorff, introduction of dissolved guano by, 311.

Oilcakes, imports of, 153;
source of nitrogen, 153.

Oil-seeds, source of nitrogen, 153.

Oligoclase felspars, 103, 214;
composition of, 103;
potash in, 220.

Organic matter, in bones, 363;
in dung, 228, 260;
in manures, 543;
not necessary for nitrifying organism, 169.

Orthoclase felspars, 103, 214;
composition of, 103;
potash in, 220.

Ox-dung, fertilising ingredients in, for food consumed, 228.

Ox-urine, fertilising ingredients in, 232.

Oxalic acid in guano, action of, 330.

Oxen, excrements of, 280;
food aided by, 280;
solid excreta voided by, 280;
urine voided by, 280.

Oxidation, 79;
products of, 79, 80.

Oxygen, absorbed by plant-roots, 81;
absorbed by soil, 81;
evolved by plants, 11;
necessary for fertility, 81;
necessary for nitrification, 52, 173;
percentage of, in plants, 39;
source of, in plants, 39.

Pabellon de Pica, guano from, 298, 302, 327;
nitrogen in, 330;
phosphoric acid in, 330.

Pacific Islands, guano from, 298.

Pacific Ocean, sea-weed in, 339.

Palagonite as potash manure, 213.

Palm-kernel meal, manurial constituents in, 282.

Pasteur, on