Decomposition of Woodij Cell-Tissue 149 



table and animal substances in the soil, and the return of 

 the carbon dioxid to the air, are accomplished by bacteria. 

 To them has been assigned the important task of main- 

 taining the proper circulation of carbon in the living 

 world, and, from the very beginning of organized life, 

 they have unceasingly worked at their task. 



The rate at which the soil-humus decays is of vital 

 concern to the farmer. Under certain conditions it 



Fig. 23. Strips of filter paper (woody fiber), showing gradual decomposition 

 by cellulose ferments. (Omelianski.) 



vanishes from the soil quite rapidly, notwithstanding 

 the utmost efforts of the farmer to enrich his soil. Large 

 applications of animal manures and the turning under 

 of green crops seem to leave no lasting effect. The soil 

 remains light in color, and capable only of retaining a 

 small fraction of the rainfall. Under other conditions, 

 the soil does not seem to digest its humus properly. 

 It becomes sour to an increasing extent, and its crops 

 languish. The same manures that rapidly disappear 

 from one soil accumulate in another. The different 

 results thus noted should be attributed to the micro- 

 organisms of the soil. 



