QUESTION OF THE SOURCES OF THE NITROGEN OF VEGETATION. 63 
amounts of ammonia applied in the manure ; but scarcely any of it as ammonia, 
nearly the whole existing as nitric acid; and this is the case although the drainage 
passes through 20 inches or more of raw clay subsoil. Lastly, direct experiments 
have shown that there is a diminution m the amount of nitric acid in the soil down to 
a certain deptli, varying according to the root-range of the crop grown, and to the season, 
but that in the depths of the subsoil below this point, the amount is again greater. 
Upon the whole, then, we are disposed to think that, in most arable soils which are 
only manured and cropped as in ordinary practice, and which have fair natural or 
artificial drainage, there is little if any loss by the evolution of free nitrogen. 
We would indeed submit, that the losses found by Dr. Frank in his series of 
7 experiments, are in all probability largely, if not entirely, accounted for by the 
special conditions of the experiments themselves to which attention has been called, 
and that those found in the rich soil, in the closed vessel, depended greatly if not 
wholly on the abnormal character of the soil itself. 
The gains (as in Experiments 4 and 5) are, however, by no means so easy to 
explain. Indeed, if there were no accidental source of error, such as all vegetation 
experiments in free air must be more or less liable to, the explanation obviously 
would be, that the free nitrogen of the air had come into play in some way. 
Dr. Frank supposes that, even in Experiments 6 and 7, where a loss was indicated, 
there had nevertheless been a gain under the influence of the plant growth, but not 
sufficient to counterbalance the loss. We would suggest that, in Experiments 4 and 
5, where a gain was indicated, there may have been no loss at all; especially in No. 4, 
with the wider vessel, and where the growth of the lupins was the most luxuriant, 
and the seed ripened; for, under such conditions, there would be much more 
evaporation, and therefore much more movement within the soil, and aeration of it. 
But, apparently giving full force to the evidence in his experiments of loss by the 
evolution of free nitrogen, and taking it as confirmation of the supposition that in 
actual practice soils suffer to a very material extent in this way. Dr. Frank says that 
all that can be concluded with certainty is—that two opposite actions are at work in 
the soil—one setting free nitrogen, and the other bringing it into combination—the 
latter being favoured by the presence of vegetation. He admits that neither his own 
results, nor those of others, afford decisive evidence as to how this takes place ; nor does 
he think that it follows from liis results, that the plant itself effects the combination. 
Independently of direct experimental evidence on the point, he considers it unlikely 
that the gain of nitrogen can be due to the ammonia of the air, because it is so small in 
amount, because the gain is by the soil rather than by the plant, and lastly, because, 
as the ammonia of the air is largely due to emanations, if it were the source w'e 
should be without explanation of the circulation of nitrogen in nature ; that is, of the 
return of free nitrogen into combination, to compensate for the losses by its evolution 
from combination. 
