200 BOTANICAL GAZETTE [September 



gave no more the characteristic nitrite formation. The genealogic 

 succession is represented in table II. 



Tests made in bouillon (of a + and — reaction) proved cul- 

 tures of series 90 and series 94 to be absolutely pure. Cultures of 

 series 86 were inoculated with i cc. of the mother culture, those of 

 series 88 with i cc, those of series 90 with i .5 cc, those of series 

 94 with 2.5 cc, and those of series loi with one large loop of 

 such a shape that it contained 2-3 drops of solution. The reaction 

 of cultures from series 94 was questionable, and microscopic exam- 

 ination of some cultures of this series showed the organism to be 

 very slow growing, so slow in fact as to allow a contamination to 

 enter during the manipulations subsequent to the first test for 

 purity. The nitrite formation of culture 10 1 was nil after nearly 

 a month, and its cellular contents nil. That the loop used in this 



TABLE II 



Solution 86 Solution ........ 94 



Solution 88 Solution loi 



Solution 90 



case was large enough for a successful inoculation, provided the 

 mother cultures were growing well, is proved by the thousand 

 other successful inoculations by this method. 



The characters of the organisms isolated during the preceding 

 series of generations are described later. Although these organ- 

 isms in the pure state tended to lose their nitrifying power when 

 cultivated in solutions at rest, by cultivating them in ignited 

 soil, to which the ordinary Omelianski solution and magnesium 

 carbonate were added, it was possible to stimulate their action 

 considerably. The cultivation of these same organisms in -solu- 

 tions undergoing a slow rotary movement and constant aeration 

 proved them to possess a very strong nitrifying power. Organ- 

 isms which were slowly losing their power of nitrification in the 

 ordinary laboratory condition, as they approached a state of 

 purity, were soon made to increase this power, up to an intensive 

 nitrification, by appropriate means (Bonazzi 2). 



