XVI TABLE OF CONTENTS 



The subject infected 270 



Immunity to pathogenic bacteria 271 



The theories of immunity 272 



CHAPTER XXIV 

 THE BACTERIAL DISEASES OF PLANTS 



Introduction 274 



Early conception 274 



Present conception 276 



The method of infection 278 



PART VII. THE DISTRIBUTION OF BACTERIA 

 CHAPTER XXV 



THE BACTERIA OF THE SOIL 



Distribution according to habitat 281 



Distribution in the soil 281 



The species of bacteria . . 283 



Bacteria in the surface layers 283 



The legume or nitrogen-fixing bacteria ...... 285 



The nitrifying bacteria 288 



The denitrifying bacteria 288 



CHAPTER XXVI 

 THE BACTERIA OF THE AIR 



Introduction 289 



Condition in the air 289 



The origin of the bacteria of the air . 289 



Quantitative distribution 291 



Seasonal distribution 291 



The species of bacteria in the air 291 



CHAPTER XXVII 

 THE BACTERIA OF WATER AND SEWAGE 



Introduction . . * . 293 



The number of bacteria in water 293 



The origin of the bacteria in water . . . . . . 294 



