33 2 
journal of Agricultural Research voi. xiv. No. 8 
EXPERIMENTS WITH AZOTOBACTER 
The general plan followed was similar to that outlined in Table V. 
The results obtained are given in Table VIII. Here, again, the extreme 
sensitiveness of Azotobacter to true acid or alkali is plainly shown. The 
limit of hydrogen-ion concentration for the growth of this organism is 
about Ph 6.5. In agreement with the results of the previous experi¬ 
ments it is clear that toward hydrogen ions Azotobacter is more sensitive 
than any of the legume bacteria used in this investigation. The narrow 
limits of growth for Azotobacter, P H 6.6 to 8.4 or 8.8, indicate that the 
growth of this organism may be used to measure the reaction of various 
substances. 
Table VIII .—Effect of the concentration of hydrogen ions on the reproduction of Azoto¬ 
bacter 
No. 
Ph. 
Azotobacter 130. 
Azotobacter 131. 
Azotobacter 130. 
1 
4.6 
5-4 
6. 0 
None.... 
None. 
2 
None. 
.do... 
Do. 
.do. 
.do. 
Do. 
Do. 
Do. 
Growth. 
O 
A 
6. 2 
.do. 
E? 
6. 4 
6. 6 
None. 
0 
6 
None. 
Growth. 
7 
8 
6.8 
Growth. 
.do. 
Do. 
7-4 
8.4 
8. 6 
.do. 
.do. 
Do. 
0 
.do.. 
.do.... 
y 
10 
None. 
11 
8. 8 
.do>. 
Growth. 
12 
9.0 
0. 2 
.do. 
13 
14 
15 
• 16 
y 
9-4 
0. 6 
None. 
None. 
y 
9.8 
.do. 
Table IX .—Effect of Rhizobium leguminosarum and of Azotobacter on the reaction of 
the culture medium 
Name of organism. 
Ph value. 
Name of organism. 
Ph value. 
Begin¬ 
ning. 
End. 
Differ¬ 
ence. 
Begin¬ 
ning. 
End. 
Differ¬ 
ence. 
Alfalfa 1. 
Alfalfa 2. 
Alfalfa 3. 
Alfalfa 4. 
Alfalfa 7.. 
Alfalfa 8.. 
Sweet clover 9. 
Sweet clover 29.... 
Red clover 13.-- 
Red clover 14. 
Soybean 16. 
Soybean 17. . 
Velvet bean 18__ 
7.2 
7.2 
7.2 
7. 2 
7.2 
7.2 
7.2 
7.2 
7.2 
7.2 
7.2 
7.2 
7.2 
7 . I 
7.0 
7.0 
7.0 
6.9 
7.0 
7.0 
7 *o 
7.0 
6.8 
7.1 
7.0 
7.2 
. 0 
Garden bean 15... . 
Cowpea 28 . 
Vetch 12 . 
Field pea 11. 
Garden pea 24 . 
Garden pea 25 .... . 
Garden pea 26 . 
Serradella 27 . 
Lupine 19 . 
Lupine 20 . 
Lupine 22.... 
Lupine 21 . 
Azotobacter 131. ... 
7*2 
7.2 
7. 2 
7 . 2 
7.2 
7 . 2 
7.2 
7 . 2 
7.2 
7.2 
7.2 
7.2 
7.2 
6.9 
7 * l 
7.0 
7.0 
6.9 
7.0 
6.8 
7 * 1 
7. 2 
7 * 1 
7 *o 
7 * 1 
5 *i 
0.3 
. I 
. 2 
. 2 
•3 
. 2 
•4 
. I 
. O 
. I 
. 2 
. I 
2. I 
