ROOT-NODULES OF LEGUMINOSAE. 99 
supplied to his flasks. Quite a good many bacteria not known to be assimilators of free 
nitrogen will make a little growth in some of the so-called nitrogen-free media. 
The chemists, therefore, have undertaken to determine whether flask cultures of Bact. 
leguminosarum show any increase of nitrogen as a result of their growth. Most have found 
no gain, or so slight a gain of nitrogen as to be within the limits of experimental error (see 
Beyerinck’s statement). Mazé is almost the only one who has reported large gains of 
nitrogen in flask cultures. I do not know what opportunities there are for error in the 
ordinary nitrogen determinations, but on the bacteriological side I detect a good many 
suspicious statements in Mazé’s papers. Miss Dawson’s comment, that Mazé’s statements 
respecting ability of this organism to store nitrogen are to be accepted only with the greatest 
reserve, appears to be entirely proper. See also Hiltner’s comments. ss 
The whole subject of the storage of free nitrogen by this organism in flask cultures and 
in the plant itself ought to be worked over again carefully by the bacteriologist and chemist. 
Possibly the root-nodules are only indicators of a fixation of nitrogen which actually takes 
place in the soil. Certainly it should be determined whether Bact. leguminosarum is able 
to fix nitrogen outside of the plant in agricultural soils both sterilized and unsterilized. 
The question why the addition of pure cultures of the organism to certain soils does not 
increase the yield of alfalfa and similar crops, should alsobe determined. Hiltner has made 
commendable attempts in this direction. Also, it should be determined why the organism 
so readily loses its virulence. There are, therefore, several fundamental problems connected 
with this question of nitrogen fixing in legumes which require further study. 
Doubts also exist in some quarters as to whether what is commonly called Bacillus 
radicicola has anything whatever to do with the production of the root-nodules. These 
doubts have been sharply focussed by Gino de Rossi who maintains that a Schizomycete 
of quite different character is thereal cause of the nodules (see abstract), and that we know 
nothing about its ability to store nitrogen. 
Hellriegel and Wilfarth postulated symbiosis. Hiltner seems to waver between sym- 
biosis and parasitism. Mazé maintains that it is not necessary to explain the fixation of 
atmospheric nitrogen by the hypothesis of symbiosis, the micro-organism being able to 
gather its own nitrogen without aid from the plant. 
SYNONYMY OF BACTERIUM LEGUMINOSARUM. 
Frank’s Schinzia leguminosarum appears to be the earliest name and therefore I 
write Bacterium leguminosarum (Frank) as the proper name for the organism causing the 
root-nodules on Pisum, Vicia, Lathyrus, etc., since it is a Schizomycete, motile by means 
of a polar flagellum (see vol. I, pp. 165-171). The type form to which this name applies 
may be taken as that causing the nodules on Lathyrus (Orobus) tuberosus. Should Hiltner’s 
view prevail respecting the existence of two distinct species, Beyerinck’s specific name 
radicicola may be retained for the organism causing the nodules on Lupinus, Ornithopus, 
and soy-bean. The name Rhizobium beijerinckii Hiltner and Stérmeris inadmissible because 
there is an earlier Bacillus beyerinckii Trevisan, and also because Kirchner’s specific name 
japonicum, applied to the organism causing the root-nodules of soy-bean, is earlier. Bacillus 
radicicola Beyr. is still earlier and the name Bacterium radicicolum may be used in place of 
Hiltner’s name. Moreover, there is some doubt whether the name Rhizobium should 
apply at all to the root-nodule organism, since Frank stated his Rhizobium to be a micro- 
coccus. ‘There is nodoubt, however, that Frank applied the name Schinzia leguminosarum 
to the zoogloee strands of this bacterium. That he interpreted them to be fungous filaments 
does not invalidate the name. 
Pseudorhizobium ramosum Hartleb (1900) is a name given to a non-infectious organism 
obtained from root-nodules. 
The name Bacillus beyerinckii was given by Trevisan (1889) to the white, liquefying, 
non-pathogenic organism isolated by Beyerinck from root-nodules. 
