Organic constituents of soils, 103. Orthoclase, 86. Oxide of iron in rocks and soils, 87, 107. Of manganese, 87. Oxygen, evolution of, by plants, 58. Influence of, on germination, 55. Presence in atmosphere, 12. Properties of, 12. Proportion of, in plants, 12. Pacquico Guano, 207. Paring, improvement of soils by, 146. Patagonian guano, 207. Pea-nut cake, 286. Peas, 286. Peat, as a manure, 203. Peat, use of, in dung-heaps, 184. Pectic acid, 46. Pectine, 46. Peruvian Guano, 205, 207, 209. Upper, 207, 213. Phosphate of lime, 96, 233. Value of, 258. Phosphates, insoluble, 258. Soluble, 237, 260. Phospho-Peruvian guano, 243. Phosphuretted hydrogen in air, 19. Pigeons' dung, 216. Plants, Albuminous constituents of, 48. Amylaceous constituents of, 40. Ash of, 64, 73. Classification of, 81. Inorganic constituents of, 9, 34, 38, 63. Oily constituents of, 46. Organic constituents of, 8. Proximate constituents of, 40. Saccharine constituents of, 40. Poppy cake, 196, 286. Potash, carbonate of, 232. Muriate of, 231. Nitrate of, 229. Plants, 82. Salts, 231. Potato, 286. Poudrette, 217. Proximate constituents of plants, 40. Pyroguanite, 236. Quartz, 86. Rainwater, 17, 18. Rape Cake, 196, 286. Dust, 195. Rocks, crystalline, 85. Composition of, 91. Disintegration of, 85. Sedimentary, 86. Roots of plants, amount of ash in, 65. Rotation of crops, 81, 266. Ruebsen cake, 286. Rye, 286. Saccharine Constituents of plants, 40. Saldanha Bay guano, 207. Salt, common, 232. Sandstones, 95. Schuebler's experiments, 127. Sea Bear Bay guano, 208. Sea weed, 200, 201. Seeds, amount of ash in, 64. Sesamum cake, 286. Sewage manure, 191. Shell sand, 246. Silica plants, 82. Silicate of potash, 233. Soda, 233. Skin, 218. Soda, carbonate of, 232. Nitrate of, 229, 260. Salts, 231. Silicate of, 233. Sodium, chloride of, 232. Soil, the, 20, 83. Influence on the composition of the ash of plants, 71. Chemical composition of, 98. Chemical and physical characters of, 83. Improvement of, by mechanical means, 137. Soil, relation of, to heat and moisture, 127. Soils, absorbent action of, 122. Air in the pores of, 114. Analysis, 101, 118. Barrenness of, 109. Classification of, 135. Exhaustion of, 81. Inorganic constituents of, 85. Mixing of, 150. Origin of, 84. Organic matters in, 103. Physical characters of, 118, 127. Sombrero Island guano, 236. Starch, 41. Lichen, 42. Stearic acid, 47. Stearine, 46. Stems of plants, ash in, 64. Straw, amount of ash in, 64. As a manure, 197. Sulphate of iron, 182. Lime, 96, 253, 260. Magnesia, 182. Ammonia, 29, 227. Potash, 231. Sulphomuriate of ammonia, 227. Sulphur in plants, 78. Sulphuret of iron, 135. Calcium, 252. Sulphuretted hydrogen, 19. Sugar, 43. Of milk, 283. Subsoil, the, 134. Ploughing, 143. Sunflower cake, 286. Syenite, 91. Tares, 286. Teelcake, 286.