Aug. 19, 1918 
Reaction on Nitrogen-Assimilating Bacteria 
327 
Table IV .—Effect of sulphuric acid on the reproduction of legume bacteria after 21 
days —Continued * 
Normal sulphuric 
acid in 100 cc. 
of medium. 
Result after 21 days. 
No. 
Concentration 
of add. 
Velvet 
. bean 
18. 
Soy¬ 
bean 
17. 
Lupine 
19. 
Lupine 
20. 
Lupine 
21. 
Lupine 
22. 
1 
Cc. 
Neutral. 
Neutral. 
Growth 
Growth 
Growth 
Growth 
Growth 
Growth. 
2 
0.025. 
NU.ooo . 
.. .do... 
...do... 
...do... 
...do... 
...do... 
Do. 
3 
0.050. 
Nl 2,000 . 
.,.do... 
...do... 
.. .do... 
...do... 
...do... 
Do. 
4 
0-072. 
NIi, 38 q . 
...do... 
...do... 
...do... 
...do... 
...do... 
Do. 
5 
0.075. 
N(1,333 . 
...do... 
.. .do... 
.. .do... 
...do... 
...do... 
Do. 
6 
o>o8o. 
N11,230 . 
.. .do... 
...do... 
...do... 
...do... 
...do... 
Do. 
7 
0.088. 
Nji, 136 . 
... do ... 
.,.do... 
...do... 
...do... 
.. .do... 
Do. 
8 
o-092. 
Nji,o87 . 
Nf 1,042 . 
... do ... 
... do ... 
... do ... 
...do... 
...do... 
Do. 
9 
0.096. 
...do... 
...do... 
...do... 
...do... 
.. .do... 
Do. 
10 
0.100 . 
Nj 1,000 . 
...do... 
...do... 
...do... 
...do... 
...do... 
Do. 
11 
0. no. 
N/qoq . 
...do... 
...do... 
...do... 
...do... 
...do... 
Do. 
12 
0.120 . 
NI833 . 
.. .do. 
...do... 
...do... 
...do... 
...do... 
Do. 
13 
14 
o- 125. 
N/800 . 
NI769 . 
...do... 
...do... 
...do... 
...do... 
...do... 
Do. 
0.130 . 
...do... 
...do... 
.. .do... 
...do,.. 
...do... 
Do. 
15 
16 
0.132 ... 
NI714 . 
N/69 0 . 
NI667 . 
.. .do... 
...do... 
...do... 
Do. 
0.135 . 
. do... 
...do... 
...do... 
...do... 
...do... 
Do. 
17 
18 
0.140... 
.. .do... 
...do... 
...do... 
...do... 
...do... 
Do. 
0.145 . 
...do... 
...do... 
. ^do... 
...do... 
...do... 
Do. 
19 
o- 150 . 
...do... 
.. .do... 
.. .do... 
...do... 
.. .do... 
Do. 
20 
0.156 . 
NI641 . 
NI625 . 
Nips- .. 
NI588 . 
NI556 . 
N!s26 . 
,..do... 
...do... 
.. .do... 
...do... 
.. .do... 
Do. 
21 
0.160 . 
None... 
None... 
...do... 
...do... 
...do... 
Do. 
22 
0.168 . 
...do... 
...do... 
.. .do.,. 
...do... 
...do... 
Do. 
23 
24 
25 
0.170 . 
...do... 
...do... 
None.,. 
None... 
...do... 
Do. 
0.180 . 
...do... 
...do... 
...do... 
None... 
None. 
0. 100 . 
. .do... 
...do... 
...do... 
...do... 
Do. 
Because of the large number of cultures used and the small difference 
in amount of acid between each culture it is possible to separate the 
legume bacteria into classes, depending on their resistance to acidity. If 
grouped in this way, the alfalfa organism would stand at the alkaline end 
of the scale, the lupine organism at the acid end. Sweet clover, vetch, 
garden pea, red clover, velvet bean, and soybean organisms would occupy 
an intermediate position and about in the order named, graded from acid 
sensitive to acid resistant. 
In the case of lupine and alfalfa, the different strains of the same 
organism show remarkable agreement and support the statement that 
the influence of acid on the lower plant, Rhizobium leguminosarum , is 
similar to the influence of acid on the higher plant, the legume. 
EXPERIMENTS WITH AZOTOBACTER 
The selection of Azotobacter was prompted by the fact that various 
investigators have reported that the growth of this organism may be used 
as an indicator of the reaction of soil. In order to test the influence of 
acid and alkali on Azotobacter, a series of mannitol cultures was pre¬ 
pared and treated as given in the preceding experiments. Three separate 
tests were made and the data recorded in Table V. In every culture in 
which acid or alkali was used a very marked effect on growth was noted. 
When compared with the legume organism regardless of the source, it is 
plain that Azotobacter is much more sensitive to changes in reaction. 
