99 



there, returns to the soil what it had taken from it, 

 viz., the elements of inorganic plant-food, and 

 transmits to its descendants the fruit of its activities 

 in the shape of organic and inorganic food available 

 for their immediate consumption. The plant in 

 its artificial state, on the other hand, is taken 

 away from where it grew,^ and not only leaves 

 virtually nothing for its successors, but, on the 

 contrary, takes away a certain quantity of fertilizing 

 substances from the soil which nature is unable to 

 restore. Water, carbonic acid, and ammonia, the 

 three great suppliers of organic food for the vege- 

 table kingdom, are brought to the plant by nature 

 herself, by rain and by the constant circulation of 

 our atmospheric air ; but not an ounce of potassa, 

 lime, or silica, not a grain of phosphoric or sul- 

 phuric acid, can nature ever restore to the soil k 

 whence the plant, which had been removed by 

 human hands, had derived it. 



Mention has been made in the preceding pages 

 that soils are divided into different classes, named 

 after the preponderating constituent ; thus we 

 speak of clayey, sandy, calcareous, and humous 

 soils. The following classification by M. Schiibler 

 is the most complete we possess, and will enable the 

 agriculturist to determine himself the description 

 of any particular soil by aid of the hints given on 

 the page following the tables. 



