Aug. 19,1918 
Reaction on Nitrogen-Assimilating Bacteria 
329 
Table; VI .—Effect of the concentration of hydrogen ions on the reproduction of alfalfa 
and lupine bacteria 
Result after 21 days. 
No. 
1. 
2 . 
3 - 
4 - 
5 - 
6 . 
7 - 
8 . 
9 - 
10 
11 
12 
13 
14 
*5 
16 
Ph. 
Alfalfa 6 . 
Alfalfa 3. 
Alfalfa 5. 
Lupine 19. 
Lupine 19. 
Lupine 21. 
4. 6 
None. 
None. 
Growth.... 
Growth. 
5-4 
6. 0 
None. 
Growth.... 
Growth.... 
Growth.... 
Growth.... 
.. .do. 
Growth.... 
Do. 
6. 2 
... do...... 
...do. 
6. 4 
Growth 
Growth.... 
Growth.... 
...do. 
Do. 
6.6 
Growth.... 
.,.do. 
.. .do.. 
Growth.... 
Do. 
6.8 
...do. 
...do. 
...do. 
...do. 
...do. 
Do. 
7 - 4 
...do. 
...do. 
...do. 
...do. 
...do. 
Do. 
8.4 
.. .do.. 
...do. 
.. .do . 
. . .do. . 
. ..do . 
Do. 
8 . 6 
...do. 
...do. 
8.8 
...do. 
.. .do. 
Q. O 
Growth.... 
Growth.... 
.. .do . 
Growth.... 
Do. 
V v 
0. 2 
Growth. ... 
None . 
9.4 
<v6 
. . .do . 
. ..do . 
Growth .... 
Growth .... 
Growth .... 
Do. 
y. 
9.8 
...do. . 
None . 
None . 
None . 
None. 
A second experiment was set up similar to the preceding except that 
only the acid range was tested. Twenty-one strains of legume bacteria 
were studied. All the data for this test are summarized in Table VII. 
An examination of the results shows clearly that the growth of the legume 
bacteria in culture solutions of varying reactions is proportional to the 
hydrogen-ion concentration of the medium, and it is probable that their 
difference in resistance to hydrogen ions is related to the reaction of 
the sap of the host plant. As shown in the data of Tables VI and VII, 
the organisms of alfalfa are the most sensitive of the legume bacteria to 
the concentration of hydrogen ions, while the lupine bacteria are the 
most resistant. In relation to true acidity, the sweet-clover, garden-pea, 
field-pea, vetch, common-bean, red-clover, soybean, and velvet-bean 
organisms occupy a position between alfalfa and lupine bacteria. The 
velvet-bean and the soybean organisms show considerable resistance to 
an increase in hydrogen-ion concentration. 
It is of interest to note the results obtained by other investigators. 
Briinn (2) found that Bacillus coli is killed within 24 hours if exposed 
to an add reaction of Ph= 4-7, but not of P H = 5.0. Wolf and Harris (25) 
reported that the difference between the reaction which just permits 
growth and the reaction which prevents growth is not great. They 
suggest the term “critical P H ” which is obtained by taking the average 
of the two values, the Pb which just permits growth and the Ph which 
inhibits growth. They found that the critical reaction for Bacillus 
welchii (B. perfringens) is about P H =4.82 and for B. sporogenes (Metch- 
nikoff) about P H =4.94. In both tests glucose peptone media were used. 
