328 
Journal of Agricultural Research 
Vol. XIV, No. 8 
Apparently the acid limit for Azotobacter is about N/1,333.3 and the 
alkaline limit of* growth about Nj 1,000. In relation to nitrates, Azoto¬ 
bacter behaves in a somewhat similar manner—that is, it is more sen¬ 
sitive to high concentrations than is Rhizobium leguminosamm (12, p. 209 ). 
Table) V.— Effect of sulphuric acid and sodium hydroxid on the reproduction of Azotobacter 
Result after 21 days. 
No. 
Normal acid or alkali ia ioo cc. of medium. 
Concentration 
of add or alkali. 
Azoto¬ 
bacter. 
130- 
Azoto¬ 
bacter 
131. 
Azoto¬ 
bacter 
130. 
I 
Neutral. 
Growth. 
Growth. 
Growth. 
2 
0. 025 cc. sulphuric acid. .. 
N 14 , 000 . . . 
....do... 
Do. 
3 
0. 050 cc. sulphuric acid. 
Nl2,000. . . . 
Do. 
4 
0. 075 cc. sulphuric acid. 
N! 1,333.... 
Trace. 
5 
0. 100 cc. sulphuric acid. 
Nil,000 .... 
None... 
None... 
None. 
6 
0. no cc. sulphuric acid. 
Nfgog . 
Do. 
7 
0. 120 cc. sulphuric acid. 
N'S 3 3 . 
Do. 
8 
0.125 cc. sulphuric acid. 
NI800 . 
_do... 
Do. 
9 
10 
11 
12 
0. 050 cc. sodium hydroxid. 
0.100 cc. sodium hydroxid. 
0. 200 cc. sodium hydroxid. 
0. 500 cc. sodium hydroxid. 
N12,000. . . . 
Nji,ooo .... 
iV/500. 
Nj 200 . 
Growth. 
None... 
Growth. 
Trace... 
None.. . 
INFLUENCE OF SULPHURIC ACID AND SODIUM HYDROXID ON THE 
REPRODUCTION OF NITROGEN-ASSIMILATiNG BACTERIA 
DISSOCIATED ACID OR ALKALI 
The marked influence of reaction upon the nitrogen-fixing bacteria, 
especially certain strains of the legume organisms and Azotobacter, has 
been pointed out in the results of this paper. The evidence submitted 
is sufficient to warrant the conclusion that sulphuric acid in mannitol 
solution is more toxic than is the hydrogen equivalent amount of sodium 
hydroxid. This difference in the action of acid and alkali may be due 
in part to their difference in dissociation. Attention was called to this 
point in an earlier paper (jo). 
EXPERIMENTS WITH ALFALFA AND LUPINE BACTERIA 
In Table VI are given the hydrogen-ion exponents for each of 16 cul¬ 
ture solutions and the growth of the organisms as shown by transfers to 
agar slopes. The cultures are arranged in order of decreasing acidity 
and the reaction of the culture medium varies as shown in the table from 
P H 4.6 to P H 9.8; the readings for the high alkaline range are not absolute. 
A study of the data shows that the alfalfa bacteria are more sensitive to 
true acidity than are the lupine bacteria. The acid limit of growth as 
shown in this test is between Ph 5.4 and Ph 6.0 for alfalfa and lower than 
P H 4.6 for lupine. In all cases there was a good agreement between the 
growth of the different strains of the same organism. 
