The Atmosphere as a source of Nitrogen to Plants. 263 
forming the bulk of the air ; Boussingault believes that it does 
not proceed from that source, but from ammonia, nitric acid, and 
possibly other compounds of nitrogen distributed through the 
air. It does not seem to me at all clear on which side the truth 
lies, at least as regards the experiments brought forward for the 
purpose ; for as to the general probability, there can be no 
manner of doubt that it would be that plants do not absorb 
atmospheric nitrogen. Why, if they did so, is a natural vegetation 
in a poor soil so small and stunted? if plants have this power, 
why is the limit to it so easily reached ? and why again does 
ammonia so wonderfully promote vegetation, whether the alkali 
is added to the soil, or, as in Ville's last experiments, to the air 
in which the plant grows ? The evidence is certainly on the 
general question strongly against the assimilation of atmospheric 
nitrogen. 
Boussingault objects to Ville's experiments, the great diffi- 
culty of entirely freeing air from ammonia by passing it through 
acid liquids, which is quite true. Ville on the other hand 
objects to M. Boussingault's experiments, the unnatural con- 
ditions under which plants are placed when growing in air not 
renewed, to which M. Boussingault replies that if the plants live, 
appear to do well, produce leaves, and provide, by the formation 
of seeds, for a continuation of their species, they cannot be said 
to be affected materially in their usual functions. 
This argument, however, does not seem to me sound. Take 
an example in the animal creation: — a man engaged in an un- 
healthy trade. He eats, drinks, sleeps, possesses locomotion, and 
begets children like otlier men, but you surely would not argue 
from all this that his trade is not unhealthy. He performs all 
his functions in spite of the disadvantages under which he labours ; 
how much better and more healthily he might have done so under 
other circumstances we can only guess. The plants in M. 
Boussingault's glass cases may have wanted the vitality to make 
use of a source of nitrogen, of which in more healthy conditions 
they might have availed themselves. It seems to me then that 
the question is not definitively settled by these experiments, valu- 
able and interesting as they are. 
It is of the less importance for our purpose that this decision 
should have been come to, inasmuch as it is admitted on all sides 
that ammonia is a most important ingredient in the air and has the 
most important effect on vegetation— Ville himself having added 
it to the atmosphere of plants with signal success. We turn 
therefore to this head. From all the experiments that have been 
quoted, we learn that a considerable but as yet uncertain quantity 
of ammonia and nitric acid exists in the air, and is brought down 
by rain — that it is larger in cities than in the country — in the 
