The Relation to Nitrogen 229 



binations. Aside from the Na of the air there may be 

 undecomposed organic matter, containing most of the com- 

 pounds of the plants and animals which it represents. 

 There is also the converted organic matter, that resulting 

 from decay, commonly designated humus, which may 

 consist, in fact, of a variety of substances. Finally there 

 is the inorganic nitrogen, including nitrates, often a small 

 proportion of nitrites, and compounds of ammonia. The 

 total nitrogen content of the soil is therefore most diverse, 

 but in productive agricultural soils there is invariably 

 a considerable nitrate content during the growing season. 

 It is probable that under exceptional conditions higher 

 plants may use to a certain extent organic nitrogen in the 

 form of amido compounds, but, practically speaking, it 

 seems certain that such organic bodies are not absorbed 

 or utilized in sufficient quantity to make this question one 

 of importance. 



122. Nitrites. The nitrites are commonly injurious, 

 and the presence of these in any quantity is a sure indica- 

 tion of unfavorable conditions. As will be shown sub- 

 sequently, they occur as temporary products during the 

 oxidation of ammonia to nitrates, but may be looked upon 

 under favorable conditions as merely transitory. 



123. Nitrates. By means of water cultures it is 

 relatively a simple matter to determine that nitrates are 

 the most favorable source of nitrogen in water or sand 

 cultures under normal conditions, and more especially 

 under sterile conditions. It is certain that such com- 

 pounds are usually absorbed by the plant unchanged. 

 Nitrates of the various nontoxic bases are therefore val- 

 uable direct fertilizers, and the data furnished by the 



