Il8 SOILS 



this purpose of organization and disorganization : the 

 first, an organization of simple materials into complex 

 substances that animal life may be possible ; the second, 

 a disorganization of complex substances into simple 

 forms that soils may be fertile, and that plants may feed 

 well and properly. 



Two constructive elements. In all life processes, two 

 constructive elements carbon and nitrogen are espe- 

 cially active. The first of these, as we have learned, is 

 obtained from the air, only from the atmospheric zone 

 in which leaves perform their important work in plant 

 building. \Ye have learned, also, that carbon, as used by 

 plants, is combined always with oxygen, in what the 

 chemist calls carbon dioxide : one part carbon and two 

 parts oxygen, hence the formula CO 2 . An abundance of 

 this compound always is present in the atmosphere, so 

 much so, in fact, that plants are never carbon-starved, are 

 never even threatened with a scarcity. For this reason, 

 carbon supply is never a problem that concerns the 

 farmer. He neither needs to know of the wanderings or 

 of the duties of carbon. It is one of the elements, that, on 

 all occasions, takes care of itself. Our interest, however, 

 is here : carbon is our greatest constructive element, and 

 the most abundantly used in the making of every organic 

 compound. 



The nitrogen problem more important In the case of 

 nitrogen we have a different problem, and for this reason : 

 plants get their nitrogen only from the soil. True, bac- 

 teria, when present in the soil, help in this work, with 

 some kinds of plants, but when not present, these favored 

 sorts are no better fitted to secure this needed element 

 than are the less favored ones. 



The two forms in which nitrogen is used by plants are : 

 as nitrates and ammonium salts. The first finds immedi- 



