470 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON 
Nitrogen. Our preliminary investigations will have enabled us to avoid, or to elimi- 
nate, all sources of error due to the incidental circumstances of the research; and the 
numerical results of a final series of experiments, showing the quantities of combined 
Nitrogen supplied, and those eventually found in connexion with the plant, will afford 
the necessary data for the solution desired. 
In discussing the conditions involved in the experiments, and the researches under- 
taken to enable us to estimate the value of those conditions, we shall arrange the sub- 
ject in such order as will most clearly bring out their bearings upon the main question, 
rather than according to the order as to time in which they were made. Several colla- 
teral experiments were made, to prove that our conditions of growth, provided in soil, 
atmosphere, and nutriment, were such as we had assumed them to be; for had they not 
been so, the object of the investigation could not be attained. The time required for 
the conduct of these collateral experiments, made it necessary that many of them should 
be performed simultaneously with the investigations the proper conditions of which 
they were designed to make known. 
We shall first consider the arrangement of the main experiments, and the plan and 
results of the collateral inquiries with a view to show what the conditions of the former 
should be, and then show how far the conditions assumed for the first year’s experi- 
ments, and those arranged in the second year, after the results of some of the collateral 
investigations were known, agree with the conditions indicated by the results of all the 
collateral investigations taken together. 
Ssecrion I—CONDITIONS REQUIRED, AND PLAN ADOPTED, IN EXPERIMENTS ON 
THE QUESTION OF THE ASSIMILATION OF FREE NITROGEN BY PLANTS, 
A.—Preparation of the Soil, or matrix, for the reception of the plant, and 
of the nutriment to be supplied to it. 
_In considering the subject of the soil to be used, the remarks made above on the 
necessity of combining the conditions of healthy growth with the simplicity of constitu- 
tion which would allow of a quantitative estimation of the results obtained, acquire a 
high degree of importance. 
So complicated is the constitution of ordinary soils, and so intimately are the nitro- 
genous compounds existing within them associated with the other matters, that it is 
impossible either to estimate the Nitrogen with sufficient accuracy for our present pur- 
pose, or to extract it from the soil without entirely destroying the other conditions of 
vegetable growth. We are, moreover, so entirely ignorant of the character of the 
organic constituents of soils, of the state in which the principal part of the Nitrogen 
exists in them, of the changes to which it is subject during vegetable growth and 
decay, and, more especially, of its relations to vegetable growth, that an ordinary soil 
could not possibly be used for our purpose. 
Our ignorance of the actual constitution of soils, as regards the state of the organic 
