Journal of Agricultural Research 
Vol. XIV, N o. 8 
318 
tomed to acid soils and (2) those forms accustomed to alkaline soils. He 
claimed that the legume bacteria of the alkaline-soil group may be so 
modified, if cultivated on acid media, that the organism will become 
adapted to an add reaction and produce nodules on the add-resistant 
legumes. 
Suchting's (22) results indicate that the legume bacteria retain their 
infecting power better in a neutral than in an acid medium. From the 
results of pot tests, Moore (18) reported that the legume bacteria would 
stand any degree of acidity or alkalinity of the soil that would permit 
the growth of its particular legume. This investigator found that legume 
bacteria flourished in media which contained as high as 0.05 per cent or 
Nf128.04 of free citric acid. According to Maassen and Muller (16) f the 
legume bacteria are very sensitive to the reaction of the medium. * 
In connection with a study of the factors that influence nodule forma¬ 
tion, Zipfel ( 26 , p. 127) noted that the legume bacteria were not very 
sensitive to small amounts of acid or alkali. According to Hiltner (75), 
the sensitiveness of lupines to liming is a result of the injurious effect of 
the lime on the nodule bacteria. Whiting (24) claims that Rhizobium 
leguminosarum is not very sensitive to the reaction of the medium. He 
agrees with Moore that in the soil, legume bacteria and their host plant 
are equally resistant to acids and alkalis. Prucha (20) studied the in¬ 
fluence of varying concentrations of hydrochloric acid and sodium hy- 
droxid on Rhizobium leguminosarum of alfalfa. He found that no growth 
occurred on agar slants containing 10 per cent of normal hydrochloric 
acid or a concentration of N/10 , and that toward sodium hydroxid the 
alfalfa organisms were much more resistant, about 30 per cent of normal 
alkali, a concentration of N/3.3 being required to inhibit the growth of 
the bacteria. The results of his experiments indicate that large amounts 
of acid or alkali inhibit the growth of the legume organism and inter¬ 
fere with its power to infect. 
Morgan and Gruzit (19) reported that an acid reaction of N/i,2oo was 
toxic to the growth of soil bacteria, while iV/7,000 alkali was approxi¬ 
mately the most suitable reaction. In a later report Gruzit (rz) found 
that the soil bacteria were very sensitive to an acid reaction. Sulphuric 
acid in a concentration of N/1,200 killed about 99.6 per cent of the soil 
flora; of Nji^oo about 93 per cent; and N12,840 inhibited the growth 
of 42 per cent of the bacteria. On the other hand, the maximum num¬ 
ber of bacteria was*noted in solutions with a reaction of N/i,ooo alka¬ 
line. The author concluded that the soil bacteria were more sensitive 
to acidity than were the corn-plant seedlings. A decrease in the number 
and activity of the denitrifying bacteria and of Azotobacter and of Rhir 
zobium leguminosarum in acid soils has been noted by Toew (75). 
From this brief review of the literature it will be seen that the results 
do not agree. An explanation for this variation may be found in the 
