402 



SOIL CONDITIONS AND PLANT GROWTH 



Organic matter in soil, relation to 

 micro-organic population, 128, 129, 

 252, 272. 



Ortstein, 137, 163. 



Osmotic pressure ; cell sap, 46, 222, 

 237. 



in relation to soil moisture, 46. 



root sap, 222, 237. 



soil solution, 125, 237. 



and classification of 



habitats, 237. 



Oxidation in soil, 175. 



— potential in soil, 177. 



— relation to fertility, 176, 283. 

 Oxygen, dissolved, effect on bacterial 



action, 275. 



— supply necessary for root, 51, 

 to plant root in swamp soils, 213. 



Paddy soils, 212, 300. 

 Pan, composition of, 164. 



— formation, 137, 162 et seq. 



as collodial phenomenon, 165. 



chemical hypotheses, 163. 



Partial sterilisation of soil, 280 et seq. 

 Pasture soils, humus of, 137. 



nitrates in, 146. 



Pathological conditions, possible nutri- 

 tion effects, 236. 

 Peat, 133, 



— English types, 134, 135. 



— Irish types, 135. 



— Scotch types, 135. 



Peat ; acidity, cause of, iii. 



— chemical analysis of, 136. 



— in relation to pan formation, 163. 



— soils, 94, 307. 



assimilation of ammonia in, 210 



denitrification and manuring 



210. 



effect of lime on, 119, 210. 



water supply in, 219. 



Perchlorates toxic to plants, 85. 



Permeability in soil, 105. 



Permutit, 156. 



Petrographic methods of soil analysis, 



121. 

 Ph value, definition of, 115. See 



Hydrogen ion concentration. 

 Phenol, decomposition of, in soil, 212, 



216. 

 Phosphate exhaustion, 321. 

 Phosphates, effect of bacteria on, 191, 



211. 

 on soil bacteria, 274. 



— in plants, economised by presence 



of silica, 78. 



— in soil, 120, 341. 

 determination of, 352, 



Phosphates in soil, reaction with dilute 

 acids, 157. 



— and plant growth, necessity for, 8, 



15, 18. 



qualitative effects, 64. 



quantitative relationships, 3^, 



64. 



Phosphatic fertilisers : increase quality 

 in crops, 67. 



use on cereals, 65. 



clay soils, 64, 312. 



• — dry soils, 65. 



fen soils, 309. 



grassland, 67, 183, 



— root crops, 64. 



Phosphorus compounds in soil, 120. 



effect on cell division, 67. 



starch transformations, 67. 



function in cell, 66. 



more in seed than in leaf, 68. 



Physical properties of soil, early studies, 

 12. 



Physiological balance of inorganic nutri- 

 ents in culture 

 solutions, 78. 



soil, 80. 



— grouping of soil organisms, 261. 

 Physiology, plant, foundation of, 9. 

 Plant food, amount in soil, 233. 

 available, 233. 



— growth, effect on soil, 296. 



soil organisms, 297. 



factors affecting, 30 et seq. 



in relation to soil types, 315. 



— ■ — optimum ratio of nutrients, 80. 

 periods in, 296. 



relation to concentration of soil 



or culture solution, 80. 



— materials from which it is produced, 



6. 



— nutrients, circulation between plant 



and soil, 93. 



— nutrition, methods of studying, 7. 

 realisation of complex nature of, 



7. 



— residues, action in soil, 213. 



decomposition in soil, 214. 



Plants, supposed resemblances to 



animals, 8. 

 Plasticity of clay, effects of, 106. 



— theories of, 106. 



Plating methods, soil bacteria, 261, 



265. 

 Ploughsole, 166. 



Poisons, inorganic, effect on plants, 

 80 et seq. 



— organic, effect on plants, 248. 

 Pore space, 220. 



Pot cultures, introduction of, 7. 



