196 BOTANICAL GAZETTE [September 



The organism from Quito soils had, according to its discoverer, 

 the following characters: a large coccus 1.5-1.7JL1 in diameter, 

 appearing larger in the living state than in the stained prepara- 

 tions. According to Winogradsky this was probably due to a 

 thick gelatinous membrane which did not stain or become invisible 

 on desiccation. Typical zooglea, as those of Nitrosomonas, were 

 never found, and the motile stage was never observed in liquid 

 cultures of this organism. Corresponding to this behavior in 

 solution, the colonies on silica jelly were only of one form, and 

 were never seen to simulate the "clair colonies" of the Nitroso- 

 monas. Surface colonies had the appearance of a yellowish liquid, 

 and like the deep colonies were also made up of free cells. The 

 organisms from Campinas and ]\lelbourne showed the same char- 

 acters, but were only different in size from the Quito organism, 

 the Campinas coccus attaining a size of 2 /x in diameter, the Mel- 

 bourne organism not quite i . 5 )U in diameter (a little smaller than 

 the other two, Winogradsky 12, 13). 



From this cursory review of the descriptions of the organisms 

 it is evident that little is known, especially with regard to their 

 cultural characters. A footnote in Winogradsky's paper (12) 

 describes a peculiar linking of the cells of the Campinas organism 

 which the author only observed once, and was not therefore in a 

 position to study carefully. It should be mentioned also that 

 this same Campinas organism gave a ''trouble sans motilite" 

 which Winogradsky could not explain. 



Criterion of purity 



One difficulty encountered in the present work was the estab- 

 lishment of a criterion of purity, a standard sufficiently accurate 

 to allow its general acceptance. The words "pure culture" in 

 bacteriological literature are used to indicate such a culture as 

 is made up completely or almost entirely of cells of the same type, 



various ubiquitous bacteria, which were not active in nitrification. The actual 

 nitrite and nitrate production in the cultures studied by Owen was so slight, to justify 

 their being considered non-nitrifying cultures, that this fact, together with the hetero- 

 geneous bacterial contents, points to the possibility that he might not have possessed 

 pure cultures of nitrifying organisms. 



