Bacteriological Studies oe the Fixation oe Nitrogen. 17 
question of seepage should be taken into consideration here as well 
as the high nitrates. 
A sample, taken near one of the apple trees, showed the soil to be 
a rather heavy clay loam. In culture it developed a characteristic white, 
gelatinous Azotobacter membrane and in thirty days gave a nitrogen 
increase of 10.15725 m. g. 
Sample No. 16. 
With Azotobacter as widely distributed as the foregoing sample in¬ 
dicated, there came the natural query, whether this genus was not in¬ 
digenous to all of our soils in a raw state as well as cultivated. To de¬ 
termine this point 1 procured my next sample July 13, 1910, from the 
top of an adobe hill which was above all ditches and consequently was 
watered only by the scant rainfall. No vegetation was growing here 
and because of its location and inaccessibility, I have my doubts wheth¬ 
er man had ever trod that particular soil before. It was literally raw 
land in the process of formation. The underlying decomposing shale 
from which the shallow soil was being made came to the surface in 
a number of places. The culture solution which was inoculated with 
an infusion of this material showed only a very slight growth, visible 
as a slight turbidity and delicate scum. In fact, this may have been 
due to the infecting substance itself. Microscopic examinations of the 
solution were made at frequent intervals but nothing which resembled 
Azotobacter could be detected at any time. After thirty days, there 
was a slight apparent increase in the nitrogen content of the culture 
but this was so very small, amounting to only .2802 m. g. that it could 
be easily accounted for by the personal equation. It was clear from the 
result obtained here that this virgin soil, at least, possessed neither 
nitrogen fixing power nor nitrogen fixing flora. 
Samples Nos. 17 and 18. 
After testing sample No. 16 and finding that it was practically 
inert so far as nitrogen fixing power was concerned, we were interested 
in learning what effect cultivation might .have upon such a soil since 
many of the orchards which have been in cultivation from 15 to 20 
years were set out in soil similar to this adobe shale. What is more, 
it is in those older orchards which have been irrigated longer and culti¬ 
vated more vigorously that we find the nitre trouble making the most 
rapid progress. If possible, we wanted to get a soil sample from a 
young orchard recently set in raw adobe shale, where there had been 
but a limited amount of cultivation. We were fortunate in securing 
just such a case. At a distance of perhaps a mile from the adobe hill 
from which sample No. 16 was taken we found a piece of raw land 
which had been broken for the first time in the fall of 1909 and set to 
young apple trees in the spring of 1910. This was watered by a high 
line ditch in which the water had not been superabundant and conse¬ 
quently it had received but little irrigation, and that during only one 
season. About the only difference between this land and the adobe 
