68 AGRICULTURAL BACTERIOLOGY. 



CHAPTER IV. 



THE TRANSFORMATIONS OF CARBON AND 

 NITROGEN. 



WE can best make our subject clear if we try to follow, as 

 closely as possible, the carbon and nitrogen in their transfor- 

 mations from one series of organisms to another as they enter 

 into the realm of vital forces, and to learn whether they go 

 through a complete cycle, being ultimately brought back to 

 the condition in which they started. If they do so then the 

 food problem is capable of solution and there need be no ces- 

 sation of vegetation. But if there is any break in the cycle 

 there will result a permanent loss and an eventual exhaustion 

 of foods. The plan of our discussion will be then, to trace 

 the elements of the food products through their circulation in 

 nature. 



PLANT FOODS. 



The two most important ingredients of plant foods are car- 

 bon and nitrogen. The first of these is obtained from the at- 

 mosphere in the form of carbonic oxide. This exists in quan- 

 tity in the air and has apparently always done so. It is 

 fruitless to speculate as to its primitive origin. The method by 

 which its supply is kept constant we shall notice presently. 



The nitrogen problem is a far more important one. Ordi- 

 narily plants obtain their nitrogen from the soil. Here are 

 found various compounds of nitrogen in considerable quantity. 

 lint not all of the nitrogen compounds in tin- soil will serve as 

 plant food. Of the various nitrogen compounds in the soil 

 there are two which stand out prominently as the chief form of 

 the nitrogen foods of plants. There are nitrates and ammo- 



