Foundation of Soil Microbiology 15 



1)\ the leguminous plants. Hellriegel and Wilfarth concluded, there- 

 tore, that the legumes took the nitrogen 'from the air through the 

 agency of bacteria existing in the nodules of their roots. (5) Schloes- 

 ing and Laurent's discovery that the weight of the nitrogen absorbed 

 from the air by the leguminous plant is al:)out ecpial to the gain in 

 nitrogen by the plant and the soil. (6) The final isolation, by Beije- 

 rinck, of the organism responsible for the formation of nodules. 



Numerous other important contributions to our knowledge of the 

 microbiological population of the soil were made during this period. 

 The work of Adametz on the fungus flora of the soil, of Miquel and 

 others on urea bacteria, of Gayon and Dupetit on denitrifying bac- 

 teria, of Hoppe-Seyler and others on anaerobic cellulose decomposi- 

 tion, and of Warington and others on the bacteria concerned in 

 the process of nitrification may serve as examples. 



Determination of the role of microorganisms in decomposition 

 processes, unfortunately, did not make such rapid progress. The 

 clear and logical ideas of Pasteur were not always successfully fol- 

 lowed by the bacteriologists and especially by the chemists, who 

 attempted to apply them to various natural processes. They were 

 very frequently confused, especially by the introduction of numerous 

 terms to explain processes that were but vaguely understood. This 

 is best illustrated by the ideas of Wollny, who summarized the 

 status of the knowledge of decomposition of organic matter at the 

 end of the nineteenth century. According to Wollny, there were 

 three different classes of decomposition, as follows: 



a. Decay or Aerobic Decomposition. This process was consid- 

 ered to be virtually a chemical "slow-burning" or "direct oxidation" 

 of the organic matter. It was believed to be similar to the "fire- 

 fanging" of manure, carried out "with or without the aid of minute 

 organisms" and "leaving essentially ash behind." The organic sub- 

 stances were said to be volatilized, the nitrogen changed to am- 

 monia, the carbon to carbon dioxide, the hydrogen to water, and 

 the sulfur to sulfuric acid. 



b. Putrefaction. When the oxygen tension was low, the processes 

 were supposed to be different. Instead of carbon dioxide, water, 

 ammonia, and minerals, various gaseous products consisting largely 

 of methane, hydrogen, carbon dioxide, hydrogen sulfide, nitrous ox- 

 ide, and nitrogen gas were believed to be formed, and the organic 

 material left behind was described as rather dark colored and 

 highly resistant to further decomposition. This residual material 

 was reported to contain, in addition to nitrogen-free compounds 



