FUNGI DECOMPOSING CELLULOSE 



83 



it is difficult to say whether the residue from the plants or the 

 mycelium of the fungi is more predominant. Even in field, 

 garden, and greenhouse soils, where the reaction is quite favorable 

 for the development of the other cellulose-decomposing organisms, 

 the fungi also play an active part in the disintegration of this 

 abundant plant constituent, especially at the early stages of 

 decomposition. This is brought out in Table 19, which shows the 

 influence of the addition of cellulose to the soil upon the develop- 

 ment of fungi, the latter being determined by the plate method. 



TABLE 19 



Influence of Cellulose upon the Numbers of Fungi in Soil 

 (from Waksman and Starkey) 



Accompanying the decomposition of the cellulose the fungi 

 assimilate considerable quantities of nitrogen, which are required 

 by the organisms to enable them to synthesize their cell sub- 

 stance. There is a fairly definite ratio between the amount of 

 cellulose decomposed and the nitrogen required, which is between 

 30 : 1 and 50 : 1; in other words, for every 30 to 50 parts of cellu- 

 lose decomposed, the organisms require 1 part of available nitrogen. 

 A large part of the carbon of the cellulose decomposed is also used 

 by the fungi for the synthesis of their mycelium. Since the 

 mycelium or microbial cell substance has a definite chemical com- 

 position and the ratio between its carbon and nitrogen content is 

 more or less constant, and since the cellulose decomposed is used 



