468 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON 
differences of plan adopted by M. Bousstneav.t and M. G. VILLE, so far as they have 
themselves described them, or in the results and explanations of other experimenters, 
any satisfactory solution of the difference of result arrived at. A priori, there are reasons 
for concluding, both from the chemical characters of Nitrogen itself, and from what we 
at present know of the chemistry of vegetation in other respects, that plants would not 
assimilate Nitrogen offered to them in the free state. On the other hand—to say 
nothing of the large total amount of combined Nitrogen actually existing—the sta- 
tistics of Nitrogen-production show that there is an amount of Nitrogen periodically 
available for the vegetation of a given area of land, the source of a considerable propor- 
tion of which is as yet not satisfactorily explained. The question whether or not the 
assimilation of free Nitrogen by plants may account for all, or a part, of the otherwise 
unexplained fixation, is seen to be left in a dilemma almost inexplicable, by the conflict- 
ing character of the results that have been recorded relating to it. Yet, as has been 
already said, upon the decision finally come to in regard to this question, must materially 
depend the degree of importance to be attached to the investigation of the other actual 
or possible sources of Nitrogen to plants, which we have briefly noticed. Under these 
circumstances, it seemed desirable that any opinions we might offer or adopt on this 
subject should have the support of such evidence as might be afforded by renewed expe- 
riment. We proceed, then, to follow up our account of the Nitrogen-statistics of vege- 
table production, the consideration of the several possible sources of Nitrogen to plants, 
and the review of the results and opinions of others on some of the points at issue, by a 
statement of our own experimental evidence in regard to this important question. 
PART SECOND. 
EXPERIMENTAL RESULTS OBTAINED AT ROTHAMSTED DURING THE 
YEARS 1857, 1858, AND 1859. 
Introductory observations. 
In laying this part of the subject before the Fellows of the Royal Society, we shall 
follow the general order in which the questions involved were presented to ourselves in 
the investigation. In so doing it will be necessary :— 
1. To consider all possible conditions to be fulfilled in order to effect the solution of 
the main question of the assimilation of free Nitrogen by plants, and to endeavour to 
eliminate all sources of error in our investigation. 
2. To examine a number of collateral questions, which have a bearing upon the points 
at issue, and to endeavour so far to solve them as to reduce the general solution to that 
of a single question to be answered by a final set of experiments. 
3. To give the results of the final experiments themselves, and to discuss their bear- 
ings upon the question which it is proposed to solve by them. 
