122 BACTERIA AND SOIL FERTILITY 



oped. Having learned that none of these were the bacteria he 

 sought, he concluded that they must be on the surface of the 

 media where inoculation had been made but no growth had ap- 

 peared. He inoculated media from material picked up from these 

 points and finally obtained the organisms he was seeking. Later 

 Klihne used silica jelly in place of gelatin. 



Winogradski found the nitrite bacteria to grow either as small 

 oval, motile rods with polar flagella or in large non-motile globu- 

 lar form. He named them nitrosomonas and nitrococcus^ re- 

 spectively. Both possess the power of transforming ammonia 

 only into nitrites. Those organisms which oxidize the nitrites to 

 nitrates he designated nitrobacter. These are small non-motile 

 rod-shaped organisms and transform the nitrites into nitrates as 

 rapidly as they are produced, and it is only under abnormal condi- 

 tions that ammonia or nitrites accumulate in a soil. 



Distribution. — Probably the nitrifying bacteria were some of 

 the first living organisms to appear upon this planet. They act 

 even yet as the pioneers preparing the soil for other plant life. 

 Miintz has found the decayed rocks of Alpine summits, where 

 no other life exists, swarming with the nitrifying bacteria. The 

 limestone and micaceous schists of the Pic du Midi, in the Pyre- 

 nees, and the decayed calcareous schists of the Faulhorn, in the 

 Bernese Oberland, offer good examples of this kind. The or- 

 ganisms draw their nourishment from the nitrogen compounds 

 brought down in snow and rain; they convert the ammonia into 

 nitric acid, and this in turn corrodes the calcareous portions of 

 the rock. Stiitzer and Hartleb have observed a similar decom- 

 position of cement by nitrifying bacteria. 



The nitrifying bacteria appear to be very widely distributed. 

 Miintz and Aubin have observed their presence not only in all 

 cultivated soils which they have examined but also in those of 

 deserts. They are not usually found in the air or in rainwater. 

 River water and sewage contain them. They are usually present 

 in well waters. In the case of deep wells their origin is due to 

 surface soil or drainage from the surface soil which has 

 found its way into the well, the water of deep wells not being 



