Apr. 14,1923 Calcium Carbonate in Nitrogen Fixation Experiments 189 
nitrogen fixation under these conditions is not known. It is possible 
that the films of aerobic fungi were a factor in maintaining anaerobic 
conditions and thereby stimulated nitrogen fixation by anaerobic organ¬ 
isms. The fungi were usually slow to develop, indicating that their 
development depended upon some subsequent change, possibly the 
accumulation of nitrogen or of calcium salts of some organic acids. The 
number of samples that failed to develop fungi films were hardly sufiicient 
to give a comparison of the quantity of nitrogen fixed in the presence 
and in the absence of a film. It is perhaps significant, however, that the 
average quantity of nitrogen fixed by the 7 samples which failed to grow 
films of fungi in the presence of CaCOg was only 2.6 mgm., compared with 
6.0 mgm. for the 76 samples producing a film. This would indicate that 
the fungus growth is in some way associated with the fixation of nitrogen 
either as a factor or as a result. 
It is evident from the preceding data that practically all soils will 
bring about the fixation of appreciable quantities of nitrogen under the 
conditions of these experiments. A large percentage of the soils examined 
however, failed to initiate the growth of Azotobacter. There are, there¬ 
fore, other organisms which are capable of fixing appreciable quantities 
of nitrogen. Such organisms seem to be quite widely distributed in 
nature. 
CONCLUSIONS 
(1) The quantity of nitrogen fixed in the presence of Azotobacter is 
greater than when it fails to develop. 
(2) The number of soils capable of initiating the growth of Azotobacter 
under the experimental conditions here described is greater by 20 per 
cent if CaCOg is added to the medium than if it is omitted. 
(3) The quantity of nitrogen fixed in a medium containing CaCOg is, 
for practical purposes, always equal to and in most cases greater than 
when CaCOg is not present in the medium. 
(4) The presence of CaCOg exerts a greater beneficial effect upon 
those organisms, other than Azotobacter, that bring about the fixation 
of nitrogen than upon Azotobacter itself. 
LITERATURE CITED 
(1) Ashby, S. F. 
1907. SOME OBSERVATIONS ON THE ASSIMILATION OF ATMOSPHERIC NITROGEN 
BY A FREE LIVING SOIL ORGANISM. AZOTOBACTER CHROOCOCCUM OF 
BEijERiNCK. In Jour. Agr. Sci., v. 2, p. 35-51. References, p. 50-51. 
(2) BeijeRINCK, M. W. 
1901. UEBER OLiGONiTROPHiLE MiKROBEN. In Centbl. Bakt. [etc.], Abt. 2, 
Bd. 7, p. 561-582, I pi. Bibliographical footnotes. 
(3) [Lipman, Jacob G.] 
1905. FURTHER CONTRIBUTIONS TO THE PHYSIOLOGY AND MORPHOLOGY OF 
MEMBERS OF THE AZOTOBACTER GROUP. In N. J. A^. Exp. Sta. 25th 
Ann. Rpt. [i903]/o4, p. 237-289, 6 pi. Bibliographical footnotes. 
(4) - 
1909. AZOTOBACTER STUDIES. In N. J. Agr. Exp. Sta. 29th Ann. Rpt. [i907]/o8, 
p. 137-143* 
(2)-and BROWif, Percy Edgar. 
191I. A LABORATORY GUIDE IN SOIL BACTERIOLOGY, iv, 87 p., I chart (fold.) 
n. p. 
(6) Lohnts, F. 
1911. landwirtschaftlich-bakteriologisches praktikum. vii, 156 p., 
40 fig., 3 pi. Berlin. 
(7) -and PiLLAi, N. K. 
1908. UEBER STICKSTOFFFIXIERENDE BAKTERIEN HI. In Centbl. Bakt. [etc,], 
Abt. 2, Bd. 20, p. 781-799. Bibliographical footnotes. 
