TRANSFORMATION OF ORGANIC MATTER 



677 



and completely decomposed than others. As a result of incomplete 

 oxidation, substances may be formed which are more resistant than the 

 original materials. In view of the fact, however, that constant synthe- 

 sis of microbial protoplasm takes place, it is often difficult to establish 

 how much of the protein has been decomposed and how much has been 

 resynthesized. The nature and extent of decomposition depend largely 



Fig. 54. Effect of nitrate upon the course of decomposition of cellulose in soils 

 of different fertility (from Starkey). 



on the organisms concerned, which in their turn are influenced by the 

 environmental conditions. Under aerobic conditions, especially in 

 aerated and acid soils, the fungi are active. Fungi attack the organic 

 material rapidly, especially in the presence of sufficient available nitro- 

 gen, and synthesize large quantities of mycelium; this is of course later 

 decomposed by the bacteria, with the result that the nitrogen is liberated 

 again as ammonia and rapidly changed to nitrate. The bacteria and 



