TRANSFORMATION OF ORGANIC MATTER 695 



rupted by lower invertebrates and bacteria. In this process, the fungi begin 

 the decomposition of the organic matter, but cannot bring it to completion. 

 Larvae of various insects and various lower invertebrates devour the mycelium 

 and the complex cells of the original organic matter covered with mycelium 

 and produce a dark mass of "humus." This is then attacked by bacteria, the 

 activities of which result in the formation of nitrates. The process of "humus" 

 formation thus consists here of three distinct biological stages: (a) growth of 

 fungi, which attack the organic matter in a preparatory manner and only to a 

 certain extent; (6) activities of insect larvae and worms, which break down the 

 organic matter, surrounded with the fungus mycelium, and prepare it for the 

 following stage; (c) "humification" proper, the bacteria beginning their action 

 probably in the body of the larvae and then continuing outside. The nitrogen is 

 changed to ammonia and then to nitrate and the ash content of the residue is 

 increased, while appreciable quantities of CO2 are produced. A muck soil re- 

 sults. A good forest soil consists of four layers: (1) an upper layer of unchanged 

 residues, heavier in the autumn when the leaves have fallen; (2) a fungus layer 

 especially active in spring and early summer; (3) a true humus layer consisting 

 of dark-colored insect excreta, mixed with decomposed and powdered leaf residue 

 rich in bacteria and animals; and (4) the first layer of mineral soil, containing 

 extractives of the upper layer washed down by rain water. In the case of My- 

 cocriny predominating, there is no dark muck layer, the unchanged mineral soil 

 following soon after the fungus layer. In some cases, the fungus layer is at a 

 minimum and the muck layer is more extensive. In the second layer the plant 

 residues are all surrounded with the fungus mycelium (the abundance of the 

 fungi under these conditions cannot be determined by the plate method, since 

 the mycelium extends throughout the soil, representing one individual. Only 

 the spores are counted by the plate method, which does not give a fair idea of 

 the abundance of growth and the nature of the population. For such studies the 

 direct microscopic method should be used). The fourth layer is ramified with 

 the roots of trees, which may also penetrate into layers two and three. The two 

 processes of decomposition of organic matter result in a constant evolution of 

 carbon dioxide and later in a continuous formation of nitrate. The first is rapid at 

 the start and then retarded; the second is at first slow, then gradually more rapid. 

 Nitrate is used up in the forest soil as soon as formed; in beaker studies in the 

 laboratory it accumulates only from layer 3. 



3. Peat formation. When fungus development is lacking or is insufficient, 

 the undecomposed leaves gradually accumulate on the surface of the soil. The 

 material can be "humified" and broken up and can also pass through the bodies 

 of animals. The chemical processes of peat formation are still unknown; 75 it takes 

 place when organic matter is decomposing in the presence of an excess of 

 water; it consists chiefly in the preservation of the carbon, in the splitting off 

 of water and the darkening of the material. The sugars, celluloses and the 

 various other constituents are rapidly decomposed, while the lignins, fats and 

 waxes are fully preserved, since the anaerobic and acid conditions do not allow 

 the development of organisms which are capable of decomposing these substances. 



75 For a full discussion of nature of humification process, see H. J. Page. 

 Fuel. 1923, August. 232. 



