202 BOTANICAL GAZETTE [September 



Temple (8), and the silicic acid jelly method of Winogradsky 

 (lo). By far the best and most reliable results were obtained 

 with Winogradsky's silicic acid method, which has now been 

 adopted in this laboratory as the best among all those tried. 

 When an impure enriched culture is inoculated in sihcic acid jelly 

 plates superficially, very little visible growth takes place. The 

 point of inoculation only assumes a perlaceous aspect and does 

 not change with age. 



When the inoculum is incorporated with the nutritive jelly 

 and incubated at 30° C, no growth is visible before 11 or 12 days 

 have elapsed from the time of inoculation. It is only after this 

 period that small colonies are visible to a magnification of 75 

 diameters, barely distinguishable in the thick mass of crystals 

 formed in the plate. After the lapse of a few days more the 

 colonies reach a size of =t:224Xi6o)u; when observed by trans- 

 mitted light they have the appearance of small yellowish masses 

 surrounded by a colorless halo, which is due to the solution of 

 the MgC03. This characteristic may be utilized as a means of 

 differentiation in the identification of the colonies (fig. i). The 

 colonies have at first dift'used outlines, and slowly take on a more 

 definite form, their appearance bejng well shown in figs. 2 and 3. 

 They never assume a hard consistency, remaining always soft. 

 Colonies of i mm. diameter have been obtained by renewing the 

 (NH4)^S04 in the plates when necessary, by the method recom- 

 mended by Omelianski. 



Hanging drop cultures 



Hanging drop cultures show no motility, even when the 

 material is taken from mother cultures which are undergoing at 

 the time a strong nitrification (figs. 7 and 8). Material prepared 

 for microscopical observation from cultures undergoing intensi\e 

 nitrification on a klinostat (Bonazzi 2) only showed a slow vibra- 

 tion of the cells, easily ascribable to Brownian movement. 



Microscopical aspect of organism 



In the beginning of the investigation the solution cultures 

 were searched for any growth which might resemble the typical 

 zooglea or the typical monad forms described by W^inogradsky 



