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 Bad. 

 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). Maze 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 Maze's papers. Miss Dawson's comment, that Maze'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. 



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 also be 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 the real 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. Maze 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 Stormeris 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 no doubt, however, that Frank applied the name Schinzia leguminosarum 

 to the zoogloeae 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. 



