The Fixation oe Nitrogen. 93 
The maximum gain in nitric nitrogen calculated per acre- 
foot per annum corresponds to five tons of sodic nitrate. 
Perhaps emphasis should be laid on the fact that these soil 
samples experimented with were, as stated, samples of an ordinary 
soil collected from the College farm at or near a point where I 
had observed the brown color which serves me as a guide and 
which I suggested was probably due to the brown azotobacter pig¬ 
ments. Further, that nothing was added to the sample except 
distilled water which had been boiled to expel any trace of ammonia 
that it might contain. 
However puzzling the facts may be they are simple; the 
nitrates are present in large quantities in areas scattered over 300 
to 400 square miles as a conservative esitmate. These occurrences 
of nitrates are independent of geological horizons and do not owe 
their origin to the neighboring or surrounding country. Nitrates 
occur in some lands surrounded by others in which nitrates do not 
occur. They are not present in the alkalis or the ground waters 
occurring in these surrounding lands; again, they occur on elevated 
mesas at such heights and under such conditions of location, that 
they could not be accounted for in this way, i. e., as concentrations 
from other lands. On the other hand we have shown that both 
fixation and nitrification take place in our soils, in a notable degree, 
and we have every reason to believe, because of the observed intense 
local developments, that our results, obtained with the samples of 
soil from Fort Collins, are much less intense than those actually 
produced in many localities. I know that there are questions un¬ 
answered, but it seems to me that it makes little difference to the 
facts, whether we know whence comes the energy which is assumed 
to be the sine qua non for the development of azotobacter or not, 
the fact is, they do develop. In our case a culture test at the 
beginning of our experiment gave unsatisfactory, but not absolutely 
negative results; another sample taken from one of the dishes, not 
inoculated, after a period of 13 days gave in four days a very 
strong membrane. The two samples were in no way comparable 
in their development. There were positive indications on the sur¬ 
face of the soil in the dish that it was becoming brown before we 
took the second sample. The rapid and profuse growth of azoto¬ 
bacter in the culture medium indicated either a very greatly in¬ 
creased abundance of the bacteria themselves or an immensely 
increased virility. The question of whether the azotobacter both 
fix the atmospheric nitrogen and convert it into nitric acid, re¬ 
spectively nitrates, or whether this latter work is done wholly.by 
another genus or other genera of bacteria is, perhaps, a question 
to be settled—but, be it settled as it may, our facts remain the same 
that we have instances of the accumulation of very large quantities 
of nitrates in our soils always associated with the brown color which 
