BACTERIA OF THE SOIL 243 



spore-producing bacilli in the soil were the most important 

 of the ammonifying bacteria. It is undoubtedly true that 

 in the laboratory in culture media these microorganisms are 

 capable of digesting proteins quite readily. Careful studies 

 of soils, however, seem to indicate that most of these species 

 are present except under unusually favorable conditions, in 

 the form of spores and that they are numerous in the soil 

 not so much because they are rapidly multiplying or are 

 present in the vegetative stage, but because there is a grad- 

 ual accumulation of highly resistant spores. The bacteria 

 apparently, which are somewhat more important in bring- 

 ing about ammonification, are members of the genus 

 Pseudomonas, particularly forms of the type Pseudomonas 

 fiiiorescens. These bacteria can likewise bring about rapid 

 ammonification in laboratory media. 



It is probably a very unusual condition for soils to be 

 markedly deficient in microorganisms capable of bringing 

 about ammonification. The bacteria are probably most 

 important in ordinary arable soil, although in some acid 

 soils, in leaf mold and in similar locations, it is probable 

 that molds are more important. 



Though the microorganisms in the soil usually are pro- 

 ducing ammonia from complex nitrogenous compounds 

 greatly in excess of their own needs, nevertheless, it must be 

 remembered that some of the ammonia is assimilated by 

 them. That is, some of the nitrogen of the soil becomes 

 locked up in the cells of the bacteria, yeasts and molds 

 present. Chemical analysis of the soil, therefore, will 

 always show a small portion at least of the nitrogen in the 

 soil in organic form. This may later be released by the 

 death and decomposition of the bacterial or mold cells. 



Nitrification. — The term "nitrification" as applied to 

 the transformation of ammonia into nitrites and finally into 

 nitrates is a misnomer chemically. The process is actually 

 one of oxidation. The name, however, has become so firmly 



