Food from the Soil 121 



are now the best soils in the world for the farmer's pur- 

 poses. Whether these crops be trees, or shrubs, or herb- 

 age, they have not only brought subsoil up to the surface, 

 but they have, at least in some cases, dissolved more than 

 they have used, and have left it all ready for the crops 

 which follow to make use of. 



But even this is far from exhausting their very impor- 

 tant list of services. Indeed, the most important of all 

 has yet to be mentioned. 



Animals cannot live either upon mineral matter or upon 

 gases, though they need both, until these have been made 

 ready for them, which they must be in the first instance 

 by vegetables. 



Plants are more independent, for they can make use of 

 mineral matter, and of gases; but they, too, need a little 

 organic matter as well, either animal or vegetable. Some 

 plants need more than others; but no soil is really fertile 

 which does not contain at least some small amount. As 

 has been shown, however, no soil is absolutely lacking in 

 this important ingredient, for wherever plants have grown, 

 or animals, however lowly, have lived, there they have 

 left their remains. 



Why plants should need organic matter is another and 

 more difficult question, which seems to be at present un- 

 answerable. All organic remains, of course, contain some 

 mineral matter; but this the plant can get from the soil. 

 They all also contain much carbon; but this the plant can get 

 without their help from the air. And finally, they all con- 

 tain nitrogen in some one or more of its compounds; and it 

 is this nitrogen which the plant wants, and cannot, appar- 

 ently, get, in sufficient quantity, except from organic matter. 



There is an abundant supply of nitrogen in the air, 



