112 



L. T. SHARP 



forms are absent in these soils. Unfortunately I have no infor- 

 mation concerning the original nitrogen fixing flora of the soils, 

 so my conclusions must be somewhat limited, but it is of scien- 

 tific interest to note that one species of the Azotohacter group 

 prevails after thirty years of drying. 



Nitrogen fixation and ammonification show somewhat similar 

 characteristics with respect to the effects of desiccation, as indi- 

 cated by the results presented in this paper. The same soil 

 proved superior in both tests of physiological efficiency. With 

 one exception, that of soil No. 5, the nitrogen fixing power of 

 the soils compared favorably with freshly sampled soils, while 

 all of the soils possessed a strong ammonifying power. The 

 power of a soil to fix nitrogen in a suitable solution does not 

 depend upon one distinct class of organisms, as does nitrification, 

 but, like ammonification, nitrogen fixation as a soil function, 

 can be accomplished by various types of organisms. In all of 

 the flasks a certain amount of organic growth occurred consisting 

 of bacteria, molds, algae, and possible yeast cells, and as proved 

 by the researches of many investigators, these lower forms of 

 life have the power of fixing atmospheric nitrogen, thus account- 

 ing for the nitrogen fixed in the culture flasks. Nitrogen fixation 

 resembles ammonification in its high resisting powers towards 

 desiccation. Neither process bears any relation to the number 

 of organisms present, nor are they similar to nitrification with 

 respect to their power to withstand drying. 



GENERAL REMARKS 



That these soils, air dried for thirty years, should still con- 

 tain a strong ammonifying flora and a fair nitrogen fixation 

 power, illustrates the remarkable persistency of organisms con- 

 cerned in those processes. On the other hand, the nitrification 

 bacteria were almost completely destroyed. This loss of the 

 active agents of an important soil function — that of supplying 

 plants with nitric nitrogen — deserves further investigation in the 

 dry regions. That a soil with a feeble nitrification power may 



2« Jour, of Biol. Chem., 10, no. 3. October, 1911, p. 169, etc. 



