QUESTION OF THE SOURCES OF THE NITROGEN OF VEGETATION. 
43 
fungus development in question has not been observed on the roots of any herbaceous 
plants. It is nevertheless a point of interest, should it be established, that by 
special means, in special cases, the organic nitrogen of the soil may serve as a supply 
of nitrogen to chlorophyllous plants. To this point further reference will be made in 
the course of the discussions upon which we have now to enter. 
PART II. 
Recent Results and Conclusions of others, relating to the Fixation of 
Free Nitrogen. 
In our introductory remarks it was stated that the object of the present paper was 
not only to discuss our own results bearing on various aspects of the question of the 
sources of the nitrogen of vegetation, but to consider the recent results and conclu¬ 
sions of others, and to endeavour to determine how far the evidence yet available is 
conclusive on the subject. And, as there can be no doubt that the Memoirs of 
M. Berthelot have materially influenced the course of inquiry in recent years, it will 
be well to commence with a statement and discussion of his results and conclusions. 
1. The Experiments of M. Berthelot. 
It was, we believe in 1876, that M. Berthelot first called in question the 
legitimacy of the conclusion that plants do not assimilate the free nitrogen of the air, 
when drawn from the results of experiments in which the plants were so enclosed as 
to exclude the possibility of electrical action. More recently he has objected to 
experiments so conducted with sterilised materials, on the ground that, under such 
conditions, the presence, development, and action of micro-organisms are excluded. 
Such objections, if valid, of course put out of court the results and conclusions of 
Boussingault, ourselves, and others, from experiments so conducted. They at the 
same time, obviously suggest, though it is true they do not actually necessitate, the 
adoption of less exact methods of experimenting—methods in which the soils, or 
plants, or both,< are almost unavoidably exposed to accidental sources of unknown 
amounts of combined nitrogen, and in which the personal equa.tion becomes a very 
prominent element. At any rate, since the announcement and acceptance of 
M. Berthelot’s objections, numerous experiments have been made without the 
enclosure of the plants; and results have been obtained showing very various and, in 
some cases, very large gains of nitrogen, assumed to be due to the fixation of the free 
nitrogen of the air in some way. 
In 1876 (‘Compt. Rend.,’ vol. 72, pp. 1283-5) M. Berthelot published the results 
of experiments in which he found that free nitrogen was fixed by v^arious organic 
compounds, under the influence of the silent electric discharge, at the ordinary 
G 2 
