654 
bacter, particularly in the presence of cellulose 
decomposing organisms. 
The high acidity of the cranberry soils 
would preclude the very idea of finding the 
Azobacter in these soils and the early students® 
of this group of organisms were of the opinion 
that they can not live in acid media at all but 
the reaction has to be adjusted first to neutral- 
ity before the conditions are made favorable 
for their activities. 
A Savannah bottom cranberry bog situated 
at Whitesbog, N. J., was used for this work. 
A part of the bog was limed three years ago 
and the crop was almost double of the corre- 
sponding plot, unlimed. Samples of the soil 
from the two plots were secured under sterile 
conditions and used for this study. The soil 
is nothing more than some white sand inter- 
woven with decayed and living plant residues. 
The hydrogen-ion concentration of the two 
soils was determined by means of the colori- 
metric method, using the phenol-sulfon-phtha- 
lein indicators suggested by Clark and Lubs.” 
The method corresponds very closely with the 
electrometric determinations using the hydro-. 
gen electrode, as was shown by Gillespie.2 A 
definite amount of soil was shaken with double 
its weight of distilled water, then centrifuged ; 
the supernatant clear liquid was syphoned off 
and used for the determination of the hydro- 
gen-ion concentration. The unlimed soil had an 
hydrogen-ion concentration of pH = 5.4 to 5.6 
while for the limed soil pH was 6.2—6.4. 
The two soils were added in 10-gram quanti- 
ties to 100 ce.c. portions of a sterile faintly 
alkaline nitrogen-free mannite solution and 
incubated at 25°. The solution in the flasks 
containing the limed soils became turbid in 
four days and a pellicle characteristic of 
Azotobacter began to develop in some flasks. 
On microscopic examination the solution was 
found to contain an abundance of Azotobacter 
cells and Actinomyces filaments. The solu- 
tion in all the flasks to which the unlimed 
soil was added remained clear as in the con- 
trol, but has shown a profuse gas production. 
6 Lipman, Ann. Rept. N. J. Agr. Exp. Sta., pp. 
262-268, 1904. 
7 Jour. Bact., Vol. 2, Nos. 1, 2, 3, 1917. 
SCIENCE 
[N. 8S. Von. XLVIII. No, 1252 
On microscopic examination no Azotobacter 
cells and no Actinomyces filaments were dis- 
covered. 
The limiting reaction for the existence of 
Azotobacter in the soil, expressed in the hy- 
drogen-ion concentration is thus found to fall 
between pH—5.4 to 5.6 and pH—6.2 to 6.4 and 
is probably nearer the latter. This will confirm 
the results of Gainey? and Christensen? that 
an hydrogen-ion concentration of the soil = 
pH—6.0 is the limiting reaction for the activi- 
ties of Azotobacter in the soil. 
The occurrence of Antinomyces filaments to- 
gether with Azotobacter cells suggests a still 
more interesting and important possibility, as- 
sociation between these two groups of soil 
microorganisms. As will be soon shown else- 
where many Actinomyces decompose organic 
residues very rapidly. The association be- 
tween these two groups of organisms, change 
of reaction, and the action of Actinomyces 
upon the nitrogen-fixation by Azotobacter is 
being studied at present in this laboratory. 
The importance of Azotobacter in cranberry 
soils, which can be effected by changing the 
reaction of those soils, thus becomes apparent: 
these organisms, whether alone or in associa- 
tion with others, utilize the plant residues as 
a source of energy and this allows them to fix 
the atmospheric nitrogen and increase its sup- 
ply in the soil, which goes towards an increased 
crop production. 
Serman A. WAKSMAN 
N. J. Acer. Exp. STATION, 
New Brunswick, N. J., 
November 2, 1918 
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