CONTENTS. 



XUI 



IV. Theory of the assimilation of oxygen and of hydrogen . 156 



V. Source and assimilation of the nitrogen of plants . . 158 

 1. The atmosphere. 2. Ammonia. Proofs . . . 159 

 Quantity of nitrogen derived from ammonia .... 161 

 Objections to Liebig's theory of the source of nitrogen . . 162 

 Form in which ammonia enters plants 163 



3. Geine or humus ........ .163 



4. Nitric acid, in the form of nitrates 164 



Necessity of supplying plants with humus .... 165 



Sect. 3. Definitions. — Source and assimilation of the inorganic 

 constituents of plants. 



Description of potassa, soda, magnesia and other salts . . 166 



" " lime, alumina, oxide of iron and silicic acid . 167 



" " hydrochloric, sulphuric and phosphoric acids 168 



Inorganic constituents. 



1. Potassa, source and assimilation 171 



2. Soda, ^^ « « 173 



3. Magnesia, " " " 174 



4. Lime, u u a 174 



5. Alumina, " " " ...... 175 



6. Silica. 7. Metallic oxides 175 



8. Phosphoric acid. 9. Sulphuric acid. 10. Common salt 176 



GEOLOGY AND CHEMISTRY OF SOILS. 

 CHAPTER IV. 



ROCKS AND THEIR RELATION TO VEGETATION. 



Sect. 1. Simple bodies which compose the rocks. 



Sect. 2. Compounds formed by the fourteen simple bodies 



I. Primary compounds, or bodies composed of two simple bodies 

 1. Acids. 2. Alkalies. 3. Urets 



II. Secondary compounds or salts 



1. Silicates 



2. Carbonates of soda, magnesia and potassa 



3. Sulphates. 4. Nitrates .... 

 5. Phosphates. 6. Muriates 



B 



180 

 181 

 181 

 181 



182 

 182 

 183 



