THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 447 
But another and potent reason for investigating the relation of plants to the free or 
uncombined Nitrogen of the atmosphere is to be found in the fact, that the question 
has, of late years, been submitted to an immense amount of research by numerous 
experimenters, and from the results obtained very opposite conclusions have been 
arrived at. Thus, M. Boussineavtt concludes that plants do not assimilate the free 
or uncombined Nitrogen of the atmosphere. M.G. VILLE maintains, on the contrary, 
that the assimilation of free Nitrogen does take place, and further, that, under favour- 
able circumstances, a considerable proportion of the Nitrogen of a plant may be derived 
from this source. Others have experimented in connexion with the subject on a more 
limited scale; and various explanations have been offered of the discrepant results and 
conclusions of M. Boussineavtt and M. G. VILtz. 
Before entering upon the discussion of our own experimental evidence in régard to 
the question of the assimilation of free or uncombined Nitrogen by plants, it will be 
desirable to pass in review the methods, results, and conclusions of M. BoussinGavLt 
and M. G. VILLE, and also of some other experimenters, who seem to have been led to 
take up the subject by a consideration of the contrary opinions arrived at by BoussINGAULT 
and VILLE. 
Section IV.—REVIEW OF THE RESEARCHES OF OTHERS, ON THE QUESTION OF THE 
ASSIMILATION OF FREE- NITROGEN BY PLANTS, AND ON SOME ALLIED POINTS, 
It has already been mentioned that, in 1837, BousstncavLt took up the question of 
the sources of the Nitrogen of Plants where DE Saussure had left it more than thirty 
years before. Dx Saussure and his predecessors had sought to solve the question, among 
others, whether plants assimilated the free or uncombined Nitrogen of the atmosphere, 
by determining the changes undergone in the composition of limited volumes of air by 
the vegetation of plants-within them. BovssineauLt pointed out that the methods 
which had been adopted were not sufficiently accurate for the determination of the point 
in question. The general plan instituted by himself, and adopted with more or less 
modification in most subsequent researches, was :— 
To set seeds or plants, the amount of Nitrogen in which was estimated by the analysis 
of carefully chosen similar specimens. 
To employ soils and water containing either no combined Nitrogen, or only known 
quantities of it. 
To allow the access, either of free air (protecting the plants from rain and dust), 
of a current of air freed by washing from all combined Nitrogen, or of a fixed 
and limited quantity of air, too small to be of any avail so far as its compounds of 
Nitrogen were concerned. And finally— 
To determine the amount of combined Nitrogen in the plants produced, and in the 
soil, pot, &c., and, so, to provide the means of estimating the gain or loss of Nitrogen 
during the course of the experiment. 
MDCCCLXI. : 3Q 
