540 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON 
no case have the results been such as to lead to the conclusion that there was an assi- 
milation of free, or uncombined, Nitrogen. 
The results of the whole inquiry may be very briefly enumerated as follow :— 
The yield of Nitrogen in the vegetation over a given area of land, within a given time, 
especially in the case of Leguminous crops, is not satisfactorily explained by reference 
to the hitherto quantitatively determined periodical supplies of combined Nitrogen. 
Numerous experiments have been made by M. Boussineauut, from which he concludes 
that free or uncombined Nitrogen is not a direct source of the Nitrogen of vegetation. 
M. G. Vitis, on the other hand, concludes, from his results, that free Nitrogen may be 
a source of a considerable proportion of the Nitrogen of growing plants. The views, or 
explanations, of other experimenters, on this disputed point, are various, and incon- 
clusive. 
It was found that the conditions of growth adopted in our own experiments, on the 
question of the assimilation of free Nitrogen by plants, were consistent with the healthy 
development of various Graminaceous plants, but not so much so for that of the Legu- 
minous plants experimented upon. 
From the results of various investigations, as well as from other considerations, we 
think it may be concluded that, under the circumstances of our experiments on the 
question of the assimilation of free Nitrogen by plants, there would not be any supply 
to them of an unaccounted quantity of combined Nitrogen, due either to the formation 
of oxygen-compounds of it under the influence of ozone, or to that of ammonia under 
the influence of nascent hydrogen. 
We have found that free Nitrogen is given off in the decomposition of nitrogenous 
organic matter, under certain circumstances. But, considering the circumstances of 
such evolution, and those to which the nitrogenous organic matter necessarily involved 
in experiments on the question of the assimilation of free Nitrogen by plants is sub- 
jected, it may, we think, be concluded that there would be no loss of combined Nitrogen 
from this cause in such an experiment, excepting in certain cases, when it might be pre- 
supposed. 
Our experimental evidence, so far as it goes, does not favour the supposition that 
there would be any loss of combined Nitrogen in our experiments on the question of 
assimilation, due to the evolution of free Nitrogen from the nitrogenous constituents of 
the plants during growth. 
In numerous experiments with Graminaceous plants, grown both with; and without 
a supply of combined Nitrogen beyond that contained in the seed sown, in which there 
was great variation in the amount of combined nitrogen involved, and a wide range in 
the conditions, character, and amount of growth, we have in no case found any evidence 
of an assimilation of free or uncombined Nitrogen. 
In our experiments with Leguminous plants the growth was less satisfactory ; and 
