520 EXPERIMENT STATION EECOKD. 



temperature of 87.5° C at the end of which time microscopical examinations 

 were made in order to determine whether the nitrifiers were present. In most 

 cases tliere was little dithculty in obtaininj? pure cultures by this method, for 

 the media used being entirely inorganic there was but little danger of contamina- 

 tion. But in order to be assured of the purity of the stock cultures used in the 

 experiments, an inorganic solid medium was prepared by thoroughly washing 

 agar-agar until the impurities and organic matter were dissolved, and then 

 adding the inorganic salts used in the liquid stock cultures. The medium was 

 prepared by adding 1.5 gm. of agar-agar to a liter of distilled water, dissolving 

 it by heating over a radial stove, and then distributing equally among 4 large 

 Ilasks. To each of these flasks was added distilled water in sufHcieut quanti- 

 ties to fill them, and this sujiply was renewed daily for 2 weeks. At the 

 end of that time the agar had been thoroughly washed, and its organic matter 

 largely lost in the process. The 4 flasks were then placed in an Arnold steam 

 sterilizer and the agar having been thoroughly dissolved, the inorganic salts 

 were added in the proportions used in the preparation of the liquid media for 

 stock cultures. 



*' The medium thus made was then sterilized in an Arnold sterilizer in the 

 usual manner, after which it was inoculated from the liquid culture and 

 plated out in petri dishes. The colonies that developed on this medium were 

 soon identified by means of microscopical examinations, as being Nitrosomonas 

 and Nitrobacter, and transfers were then made to a flask containing liquid 

 media of the same composition as that from which the agar ■svas inoculated. 



" The stock cultures thus prepared proved very satisfactory, and this method 

 of isolating the organisms was used almost entirely in the investigation. The 

 use of washed agar gave much better results than that of Winogradski's silicic 

 acid medium, since the colonies developed more rapidly upon the former, and 

 the agar having a smoother surface, the bacterial development was more clearly 

 defined, and therefore more easily detected." 



Culture media in which the supply of carbon in inorganic form (magnesium 

 carbonate, calcium carbonate, potassium carbonate, and free carbon dioxid) 

 varied were inoculated with these organisms and the rate of formation of 

 nitrites and nitrates noted. 



A special flask designed by the author for the investigations which required 

 the elimination of the carbon dioxid of the air is described. 



The author concludes from the results obtained that nitrification is affected 

 by carbonates and that magnesium carbonate is more efficient than the other 

 carbonates tested in promoting the growth of nitrifying organisms. He also 

 concludes that " the nitrifying organisms of the soil do not depend to any 

 appreciable extent on the carbon dioxid of the air for their carbon supply." 



On the present state of knowledge of micro-organisms which fix free 

 nitrogen, L. Palmans {Ann. Gembloux, 18 (1908), No. 5. pp. 289-309).— This 

 is a review with a bibliography of 60 references to literature of investigations 

 on the subject. 



Utilization of the nitrogen of the air by plants, T. Jamieson (Ann. Sci. 

 Agron., 3. ser., 2 (1907), I, pp. 1-^6). — This is a reprint in Fi-ench of a revision 

 of the original paper on this subject (E. S. R., 19, p. 127). 



Nitrogen fixation for nonleguminous plants, W. B. Bottomley (Country 

 Life [London], 23 (1908), Xo. 598. pp. 899, 900, figs. 5).— This article briefly 

 discusses the possibility of aiding the growth of nonleguminous plants by 

 inoculation of the soil with nitrogen assimilating organisms, and refers to recent 

 experiments by the author with oats, barley, cabbage, turnips, radishes, beets, 

 strawberries, etc., which it is claimed have given promising results. 



