16 EXPEKIMENT STATION RECORD. 



produced by either of the other species. A. heyeri)icki and A. chroococcum, 

 while quite different in their cultural characteristics, are physiologically alike 

 in so far, at least, as their power of nitrogen fixation is concerned. Like A. 

 vinelandii, these two species may also increase their output of combined nitrogen 

 when growing together with certain smaller bacilli." 



Investigations on the biology of nitrogen-fixing bacteria: A contribution 

 to the knowledge of the variations in nitrogen content of bare soils, H. 

 Wakmboli) (iMinUr. Jahrb., 35 {1906), No. 1-2, pp. 1-123; ahs. in Clicm. Centbl.. 

 1006, I, No. 12, p. lO-'il). — In this article the author reviews with considerable 

 fullness previous investigations on denitrification and nitrogen fixation in the 

 soil, discusses the general conditions controlling such changes in nature, and 

 reports a series of experiments on the influence of temperature, water content, 

 aeration, associative action of pure and mixed cultures, etc., on these processes. 



The principal conclusions drawn from the results obtained are as follows : 

 Sterilized soils of very porous structure, containing IG to 30 per cent of water, 

 when subjected to thorough aeration fixed nitrogen to an appreciable extent, 

 indicating that under certain conditions there is a chemical fixation of nitrogen 

 in the soil without intervention of organisms. This is in agreement with 

 results obtained by Berthelot. The increase in nitrogen of both sterile and 

 unsterilized soils was dependent to a considerable extent upon the temperature. 

 The water content of thin layers of porous soils in which aeration was not 

 interfered with exerted no appreciable influence on the nitrogen content of the 

 S()il. In pot experiments with larger amounts of soil (about 13* kg.) the water 

 content exerted a very appreciable influence. In such cases the most desirable 

 water content from the standpoint both of preservation and increase of nitrogen 

 in the soil was 20 per cent. With 10 per cent and less there was either no 

 increase or a very decided decrease of soil nitrogen, the loss of nitrogen being 

 especially large in case of the lighter soils. • The loss of nitrogen with a water 

 content of less than 3 per cent can not be ascribed to denitrifieation, but must 

 be due to some purely chemical process, since nitrates were not present at the 

 beginning of the experiment and the nitrifying organisms could not develop 

 with so small a water content. 



The growth of algjie on the surface of the soil favored an increase of nitrogen 

 in the soil, but it is not clear whether this was due to nitrogen assimilation by 

 the alga^ or to their influence in retarding denitrification. With large amoun.ts 

 (about 3 kg.) of sterile soils a water content of 3 to 20 per cent did not influence 

 the nitrogen content. With a water content of 30 per cent, however, a loss was 

 observed. No influence of aeration on the nitrogen content of soils was observed 

 in case of small amounts (150 gm.) of soils in thin porous layers either in sterile 

 or in unsterilized condition. In pot experiments with about 13^ kg. of soil 

 and 15 per cent of moisture thorough aeration increased the nitrogen content. 



The use of artificial humus favored the fixation of nitrogen, indicating that 

 this material is a suitable source of carbon in artificial culture media for soil 

 bacteria. With a temperature of less than 5° C. or greater than 00° C. there 

 was no fixation of nitrogen in the artificial cultures. The most favorable tem- 

 perature zone for nitrogen fixation in artificial cultures lies between 18 and 

 Sl° C. Wide variations were observed in the capacity for fixation of nitrogen 

 of the various organisms experimented with, both in pure cultures and in mixed 

 cultures. In artificial cultures of azotobacter weak diffused light appeared to 

 exert a favorable influence upon nitrogen assimilation. 



Some work of the Agricultural-Bacteriological Institute of Gottingen 

 University, A. Koc n (.1////. lu-ui. Laiidir. (Icxell.. 21 (1906), No. 10, pp. 

 111-115). — A brief review is given of recent investigations at this institute on 



