TABLE OF CONTENTS XV 



v 

 CHAPTER XX 



PAGES 



Organisms in the Soil 421-442 



Macrooryanisms. 



Rodents, 342— Worms, 343 — Insects, 344— Large 

 fungi, 345 — Plant root, 346. 



Microorganisms. 



Plant microorganisms, 347 — Plant microorganisms 

 injurious to higher plants, 348 — Plant microorganisms 

 not injurious to higher plants, 349 — Bacteria, 350 — 

 Distribution of bacteria, 351 — Numbers of bacteria, 352 

 — Numbers as influenced by season, 353 — Conditions 

 affecting growth, 351 — Oxygen, 355 — Moisture, 356 — 

 Temperature, 357 — Organic matter, 358 — Soil acidity, 

 359 — Functions of soil bacteria, 300 — Decomposition 

 of mineral matter, 361 — Influence of certain bacteria 

 and molds on the solubility of phosphates, 362 — Decom- 

 position of non-nitrogenous organic matter, 363 — De- 

 composition of nitrogenous organic matter, 364. 



CHAPTER XXI 



The Nitrogen Cycle 443-474 



Decay and putrefaction, 365 — Ammonification, 366 — 

 Bacteria and substances concerned in ammonification, 

 367 — Nitrification, 3(58 — Effect of organic matter on 

 nitrification, 369 — Effect of soil aeration on nitrification, 

 370 — Effect of sod on nitrification, 371 — Depths at 

 which nitrification takes place, 372 — Loss of nitrates 

 from the soil, 373 — Nitrate reduction, 374 — Nitrate 

 assimilating organisms, 375 — Denitrification, 376 — Ni- 

 trogen fixation through symbiosis with higher plants, 

 377 — Relation of bacteria to nodules on roots, 378 — 

 Transfer of nitrogen to the plant, 379 — Soil inoculation 

 for legumes, 380 — Nitrogen fixation without symbiosis 

 with higher plants, 381 — Nitrogen-fixing organisms, 382 

 — Mixed cultures of nitrogen-fixing organisms, 383 — 

 Nitrogen fixation and denitrification antagonistic, 384. 



