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]