INFLUENCE OF REACTION ON NITROGEN-ASSIMILAT¬ 
ING BACTERIA 1 
By E. B. Fred, Agricultural Bacteriologist , and Audrey Davenport, Technical 
Assistant, Agricultural Experiment Station of the University of Wisconsin 
INTRODUCTION 
One of the most powerful factors influencing the growth of legume! is 
the reaction of the soil. Indeed, it has been known for a long time that 
alfalfa, clover, and related plants will not thrive on an acid soil. Some 
idea of the importance of this problem may be seen from the vast amount 
of literature dealing with this subject which has appeared in recent years. 
These reports are concerned largely with the nature of the add constitu¬ 
ents of the soil and with their influence on the growth of the higher plant. 
Details of these investigations are not essential here, since this paper 
presents the results obtained in a study of the influence of addity on 
bacteria rather than on higher plants. Because of the intimate relation 
between host plant and bacteria in the case of legumes, it seems that the 
results of these tests may be useful in explaining the influence of soil 
addity on legumes. 
A number of sdentists have noted in a general way the effect of total 
addity or alkalinity on the nodule-forming bacteria and on their host 
plants. Their results are of interest, but they fail to give information 
in regard to the proper reaction for the growth of the bacteria without 
the host plant. Repeatedly the question is asked, How long will the 
legume bacteria live in soil in the absence of the legume? Undoubtedly 
the answer to this question involves a study of many factors, among 
which reaction is important. It is the purpose in this work to establish 
the relation of Rhizobium leguminosarum from different plants to add 
and to alkali. 
Before presenting the results obtained a brief review of some of the 
previous contributions to this subject will be made. 
HISTORICAL REVIEW 
More than 30 years ago Beijerinck (1) 2 in his study of Rhizobium 
leguminosarum noted that this organism is injured in a medium of Nj33.3 
to Nj$o concentration of acid. He found that a medium prepared from 
a decoction of pea stems, reaction Nj 166.6 malic acid, gave optimum 
conditions for growth. 
From his observations Maz& (77) conduded that the legume bacteria 
may be divided into two great groups: (1) Those forms which are accus- 
1 Published by permission of the Director of the Wisconsin, Agricultural Experiment Station. 
2 Reference is made by number ( italic ) to "Literature cited,” p. 335-336. 
Journal of Agricultural Research, Vol. XIV, No. 8 
Washington, D. C. (317) Aug. 19, 1918 
Key No. W1S.-13 
64613°—18 - 3 
