Bacteriological Studies oe the Fixation of Nitrogen. 15 
ent time no injury has been observed in the orchard. The same brown 
color was very marked along the roadside where the irrigating water 
had been running three days previously. With this soil taken from the 
furrow, a yellowish brown membrane, consisting largely of Azotobac- 
ter, was obtained, and upon analysis the culture showed an increase of 
7.7055 m. g. of nitrogen in thirty days. 
Sample No. ii. 
Sample No. 11 was obtained from an alfalfa field located on river 
bottom land where the water was quite near the surface. Five to ten 
acres of alfalfa had died and the barren spots were brown to black on 
the surface. The soil was a light alluvial formation and admirably 
suited to agriculture. The top four inches were taken for examination 
June 1910. In culture it developed a heavy straw colored, leathery 
membrane, after 48 hours, which was composed of Azotobacter cells 
with many large and small rods. After thirty days, an increase of 
5.11365 m. g. of nitrogen was obtained. 
Sample No. 12. 
A complaint was received from a certain truck gardener in July 
1910, stating that there were places in his garden where, for several 
years, he had been unable to secure a satisfactory stand. At that time, 
his chief trouble was with carrots and parsnips. Three to five acres 
were involved this season, and from the brown appearance of the sur¬ 
face and mealy character to the tread, the soil looked very suspicious. 
It was a nice sandy loam and no trouble was ever experienced in rais¬ 
ing crops except on the barren spots. Even on these, when the plants 
became once established, they grew very luxuriantly. A sample con¬ 
sisting of the three inches of top soil, taken about ten feet from a bar¬ 
ren place, was procured. This yielded a heavy, wrinkled, pale yellow 
membrane, which browned with age. Azotobacter was abundant and 
after thirty days our analysis showed an increase of 8.61615 m. g. of 
nitrogen in the culture. 
Sample No. 13- 
We come next to an orchard where the burning first appeared in 
1909 on the apple trees. The point of particular interest in this case 
is the marked resistance which a block of pear trees has shown to the 
nitre. There are about three acres of these trees in full bearing and, 
although lying adjacent to a five acre apple orchard which is badly af¬ 
fected, and in the direct path of the nitre streak, the first injured pear 
tree is yet to be seen. As a matter of fact, this immunity of the pear is an 
occurrence of rather frequent observation. The apple orchard embraced 
about seven acres and the trees were all from twenty to twenty-five 
years old. They had been in perfect condition and yielding abundant¬ 
ly until the summer of 1909 when the burned leaves began to make 
their appearance. A section in the center of the orchard of about one 
half acre, succumbed that season, but before July, 1910, when I took my 
sample, three more acres had died and had been pulled up and the 
