4 CONTENTS. 



CHAPTER XIII. 

 Sources of the Carbon of Plants 7883 



CHAPTER XIV. 

 Sources of the Nitrogen of Plants 8492. 



PART SECOND. 



CHAPTER XV. 

 Inorganic Elements of Plant Growth .. 93 98 



CHAPTER XVI. 

 The Ash of Plants and its Composition 99106. 



CHAPTER XVII. 



Compounds of the Inorganic Elements of Plants 107118 



CHAPTER XVIII. 

 The Soil. Its Composition 119122 



CHAPTER XIX. 

 The Rocks. Their Composition and Relations to the Soil 123 129 



CHAPTER XX. 

 Physical Properties of the Soil 130 14a 



PART THIRD. 



CHAPTER XXI. 

 Exhaustion of the Soil 144154 



CHAPTER XXII. 

 Mechanical Improvement of Soils 155166 



CHAPTER XXIII. 

 How to Drain Land 167172 



CHAPTER XXIV. 

 Irrigation of Farm Crops 173177 



CHAPTER XXV. 

 Plowing. Its Purposes and Results 178 -18a 



CHAPTER XXVI. 

 Harrowing. Its Effects upon the Soil and Relation to the 



(irouth of Crops 184187 



CHAPTER XXVII. 



Cultivating. Its Effects upon the Soil and the Growth of Crops 1S8 191 



CHAPTER XXVIII. 

 Manures. Their Mechanical Effects upon the Soil 192 195- 



