CONTENTS 



TXl 



PAGE 



The Ptomaines 268 



The Putrefying Process 268 



Summary 269 



CHAPTER XXIV 

 The Fertility of the Soil 



Exhaustion of the Soil 271 



Natural Fertility 271 



Fertilizers 271 



Animal Wastes 272 



Microorganisms 272 



The Nitrifying Bacteria 273 



The Nitrite Bacteria 273 



The Nitrate Bacteria 274 



Nitrifying Organisms and Higher Plants 274 



Effects of Cultivation 274 



Free-living Soil Bacteria 275 



Bacteria Symbiotic with Algae 275 



Tubercle Bacteria 276 



Mycorrhiza 276 



Denitrifying Bacteria 276 



Sulphur Bacteria 277 



The Carbon Cycle 277 



The Nitrogen Cycle 277 



Sulphur and Phosphorus Cycles 279 



The Energy Cycle 279 



PART II 



Section 8. Growth and Reproduction 



CHAPTER XXV 



Cell-Division 



The Growth of Organisms 283 



Cell Growth and Division 283 



The Mechanism of Cell Division 285 



The Resting Nucleus - 285 



The Behavior of the Chromatin . . 286 



The Formation of the Nuclear Spindle 288 



The Splitting of the Chromosomes 288 



The Anaphase 288 



/ The Telophase and Reconstruction of the Nucleus 289 



/ The Individuality of the Chromosomes 289 



I The Division of the Cell-Body 290 



Summary 290 



