226 Bulletin 247. 



instance been collected by others, to whom credit will be given. I have 

 not attempted to give all the data of any of these experiments, but only 

 such as seem to have a bearing directly or indirectly on the question 

 under consideration. On the other hand, I have tried to give faithfully 

 all the data that might influence a judgment on the subject. Some of 

 the data presented tends to disprove the thesis of the paper and for this 

 reason, if for no other, further investigations are desirable. 



Difference between nitrogen and other elements. 



As a matter of course, every element has one or more characters 

 which distinguish it from other elements or it would not be recognized 

 as a separate element. It may be well to recall some of nitrogen's char- 

 acteristics. It is no part of the original earth's crust. It belonged ex- 

 clusively to the atmosphere to which it tends constantly through denitri- 

 fication, to return, while other forces tend to add it to the soil. In its 

 normal atmospheric condition it is not directly available to any higher 

 plant, in which it differs from oxygen and carbon-dioxid, both of which 

 are taken freely from the atmosphere by all higher plants. The nitrates 

 of the soil differ from the phosphates in that they move through the soil 

 readily and are easily removed therefrom by leaching. Potash salts are 

 also readily removed from the soil but, unlike the phosphates, they occur 

 in the original earth's crust in comparatively larger quantities. 



The function of nitrogen. 



The living part of all plants is protoplasm. The element which 

 above all others concerns us in the production of proteids is nitrogen. 

 This is about all that is positively known about the function of nitrogen 

 in the growth of plants. The usual statement is that the green color of 

 plants is due to chlorophyll and that chlorophyll, for its normal develop- 

 ment, requires iron. Every one knows that the immediate result of ap- 

 plying soluble nitrogen to the soil is to cause vegetation to assume a 

 greener color. Just what part does nitrogen play in bringing about this 

 result? If it were demonstrated that nitrogen played a direct part in 

 making plants green, it would be completely demonstrated that nitrogen 

 acted directly as a plant-food. 



Relation of total and zvater-solnble nitrogen. 



Since in this paper, the discussion largely concerns water-soluble 

 nitrogen, it is desirable to state exactly what is meant by water-soluble 

 nitrogen and what is its relation to total nitrogen and what relations 

 have either to the needs of plants. 



The Bureau of Soils has developed a method of determining the 

 water-soluble nitrates which consists of stirring a given weight of soil in 



