OP AGRICULTURE. 201 



not only in the grain and seed, but in the straw and 

 stalk. Every exact analysis of the ashes of trees, 

 shrubs, and plants of every kind, cultivated or wild, 

 shows the presence of phosphoric acid. 



Having briefly discussed the mineral ingredients of 

 the soil and their chemical action, we will now turn 

 our attention to the organic or vegetable constituents 

 of the soil. 



CHAPTER IY. 



THE VEGETABLE, OR ORGANIC CONSTITUENTS OF THE 

 SOIL. 



Soil consists of two grand divisions of elements: 

 inorganic and organic. The inorganic are wholly 

 mineral, formed by chemical action on the metallic 

 and unmetallic elements of rocks. They existed 

 before plants or animals. Life has not called them 

 into existence, nor created them out of the simple 

 constituents. Organic elements are the product of 

 living organs, or of substances once endowed with 

 life, hence called organic ; and, when formed, they 

 are subject to chemical laws. The number of 

 elements in the organic parts of the soil does not 

 exceed four, viz: oxygen, hydrogen, carbon, and 

 nitrogen. 



To have a clearer idea of this subject, we will give 

 a description of each of these elements separately. 

 * Oxygen (symbol O ; combining weight 8). 



This is one of the most important, as well as the 

 9* 



