SUBJECT INDEX 



403 



Pot cultures, modern methods, 356. 

 Potash in soil, determination of, 352. 

 Potassic fertilisers, effect on leguminous 



crops, 72. 

 value for thin soils or dry dis- 

 tricts, 340. 



in unfavourable seasons, 71. 



Potassium compounds in soil, 120, 339. 



distribution among soil 



particles, 121. 

 reported harmful effect on soil, 



116. 



— function in cell, 72. 



— in plants, economised by presence 



of sodium, 73. 



— salts, absorption by soil, 157. 



effect on bacterial action, 274. 



influence on nitrogen effects, 63. 



necessary for plant growth, 7. 



qualitative effects on plant, 6g. 



quantitative relationships, 31. 



suggested replacement in cell by 



equi-radioactive elements, 72. 

 Potatoes, quality in, 318. 

 Potsherds, effect of adding to soil, 52. 

 Prairie soils, loss of nitrogen from, 



181. 

 Principles of vegetation, search for, 2. 

 Protein content of grain. See Nitro- 

 gen. 



— metabolism ; relation to calcium, 74. 

 Protozoa in soil, 288 et seq. 

 inverse relation to bacteria, 



292. 



numbers of, 291. 



Putrefactive power (Remy), 263. 



Radio-activity an \ potassium supply, 

 72. 



of soil, 89. 



Radium, effect of, on plant growth, 89. 

 Rainfall and crops, effect, 45. 



— effect on scheme of manuring, 341. 

 — soil, 119, 235, 330. 



Rain water ; ammonia and nitrate in, 18. 



chlorine content, 76. 



dissolved oxygen in, 228. 



sulphates in, 76. 



Reaction of soil ; methods of controlling, 



244- 



Reactive inorganic constituents of soil, 

 109, 215. 



Reclamation of clay soils, 312. 



sandy soils, 314. 



Renewal of plant nutrients, effect of rate 

 of, 239. 



Respiration of plants, general pheno- 

 mena, 10. 



Resting period of plants, 88, 



Ripening processes hastened by phos- 

 phates, 65. 



drought, 65. 



Rohhumus, 138. 



Rothamsted experiments, commence- 

 ment of, 17. 



results, 18, and many subsequent 



pages. 



Root, activity of, makes soil alkaline, 

 296. 



— crops, use of phosphatic fertilisers, 



64. 



— development, increased by phos- 



phates, 64, 341. 



marked in sandy soils, 316. 



impeded in clay soils, 64. 



— excretion, nature of, 33, 233. 



of mineral matter, 296. 



possible toxic, 244. 



— formation of, increased by aeration, 



53. 



— calcium salts, 74. 



— phosphates, 64. 



influence of soil type, 64. 



water supply, 44. 



— functions of, id. 



— sap, acidity of, 81. 



concentration of, 222, 237. 



osmotic pressure of, 222, 237. 



Rotation of crops, 184, 244. 



not essential, 5. 



statistics of, 13. 



Saltpetre promotes vegetation, 7. 



— the " principle " of vegetation, 3. 

 Salts, alkali, effects on plants, 85. 



soil bacteria, 274. 



Sand, composition of, 102. 



— cultures, methods of, 356. 



— dune, 109. 



— effect in soil, 108. 

 masked by organic matter, 



132. 



— properties of, 108. 

 Sandy soils, 302, 312. 



characteristics of plant growth 



in, 312. 



need no excess of calcium carbon- 

 ate, 119, 336. 



subject to pan, 163. 



water supply in, 219. 



Scouring land in Somerset, 317. 



Seasonal effects on bacterial activity in 

 soils, 276. 



— variation in activity of soil organ- 



isms, 279. 

 Seed, composition of, 68, 74, 75. 



— effect of length of ripening period,54. 

 manuring, 44. 



26* 



