Darwin's experiments, 11, 56 Deltas, 122 Drainage, 19, 96 Dwellers in the soil, 53-63 Earthworms, 54-56 Error of experiment, 48 Fallow, 14, 95 Fens, 112 Flora, 114 Fords, 126 Frost, action of, on soil, 83 Grassland, 75 Grit, 6 Hales's experiment, 73 Heaths, 104 Heavy soils, 100 Hoeing, 86-93 Humus, 36, 51, 93, 125 Hypotheses, 36 Land slips, 12 Leaf mould, 33 Light soils, 104 Lime, action of, on clay and soil, 19-21, 96-98 Lime water, 19 Loams, 2, 65, 108 Marsh gas, 40 Micro-organisms, 56-62 Moorland, 80 Mulch, 87, 90 Peat, 37-40, 130 Peat bogs, overflow of, 38 Perspiration of plants, 74 Plant food, 41-52, 62 Plant requirements, 64 Ploughing, 82 Pot experiments, 41-52, 54, 69, 71 Roads, 30-32, 101-112 Rolling the soil, 84 Sand, 6, 22-32, 41 Sand dunes, 22 Sandy soils, 68-72, 102-108 Shrinkage of clay, 10 Silt, 7 Soil sampler, 82, 88 Sowing seed, 84 Springs, 24-31, 111 Subsoil, 2, 4, 42, 48-51 Swelling of clay, 11 Swelling of peat, 38 Temperature of soil, 86-93 Tilth, 86 Van Helmont's experiment, 46 Villages, situation of, 24, 30, 126 Wastes, 101, 104 Water content of soil, 88-93 Water, movement of in soils, 65-68 Water supply and plant growth, 69-74 Weathering, 116 Weeds, 94, 97 Woodland, 80, 101