igS BOTANICAL GAZETTE ^September 



before any attempt to determine the purity by the bouillon method 

 is made; (2) the bouillon used in testing for purity should be of 

 an alkaline reaction; better results would be obtained if the 

 testing were made in bouillon of different reactions; (3) the time 

 limit necessary for absolute reliability for the growth in bouillon 

 should be fixed at 10 or more days; (4) the inoculum used in test- 

 ing for purity by the bouillon method should be as large as 

 permissible by ordinary technic; (5) microscopical examination 

 must reveal a picture uniform within the limits of individual 

 morphological variation in the species and within the different 

 phases of the same organisms, provided such phases are established 

 as correct. 



A study of the growth of different organisms on the same 

 medium and the description thereof is often relied upon as a diag- 

 nostic method. At best this method is unsatisfactory and of 

 limited application. This is plainly shown by the fact that we 

 cannot attempt to compare, on the same basis, the ordinary sapro- 

 phytic and parasitic organisms with such organisms as will not 

 grow on the media used in ordinary laboratory practice. The 

 known organisms of the latter type are not numerous at present, 

 but doubtless they are quite abundant in nature. The nitrite- 

 formers of WiNOGRADSKY are to be classified among the latter, 

 together with the not less peculiar B. oligocarho philus , B. panto- 

 thropus, and some organisms of the oligonitrophilus, sulphur, and 

 iron groups. In the case of these organisms a study of their 

 morphology in a few special media will lead to more accurate and 

 reliable results than any attempt made to grow them in bouillon, 

 gelatin, or agar of the ordinary composition. 



Having presented the description of the South American 

 nitrite-formers, and the criteria of purity followed in the present 

 work, a description of the organism isolated to comply with these 

 rules, from a North American soil, will be given after a discussion 

 of the isolation technic. 



Experimental 



After establishing nitrification in solution by means of a small 

 soil inoculum, the growth of the organism concerned was stimulated 

 by continued additions of new doses of ammonium sulphate, new 



