MODE OF DECOMPOSITION. 763 



important mineral and nitrogenous substances (potash, phos- 

 phoric acid, ammonia, etc.), which combine with various 

 compounds formed in solution by humus, and are retained by 

 it, ready for absorption by the roots of trees. 



The residual products of the decomposition of humus, are 

 ash constituents, carbon-dioxide and water ; they are either 

 quite pure, or in the form of salts that are the food and 

 manure of the forest. By the ash- constituents, set free by 

 the decomposition of humus, most of the nutritive matter that 

 the production of wood has taken from the soil, is returned to 

 it in the most assimilable condition. 



From the successful use of manure in agriculture, we can 

 see how greatly the growth of plants depends on these ash- 

 constituents, also prove the good results obtained by manuring 

 our nursery lines and seed-beds, and the difference between 

 the production of wood on soils that are rich, or poor, in 

 nutritive mineral matter. 



Nowadays foresters are more and more favourable to the 

 use of artificial manures for forest plantations, as well as for 

 forest nurseries (Jentsch, Schwappach, Giersberg, Mathes, 

 Baumann, Fricke and others) ; so also the sowing of legumi- 

 nous plants, as accumulators of nitrogen, has been found 

 beneficial to impoverished soil. 



SECTION III. MODE OF DECOMPOSITION OF FOREST LITTER. 



It is well known that the decomposition of organic sub- 

 stances is effected only by bacteria and fungi,* the species of 

 which are affected, relatively and absolutely, by the reaction of 

 the soil (acid, neutral or alkaline); probably the acid products 

 of humus are due to low organisms. If the layers of litter 

 become dry, the process of decomposition is interrupted and 

 unfavourable kinds of humus are formed. 



The comparative rate of the decomposition of forest-litter 

 and humus is influenced chiefly by the kind of soil-covering, 

 soil, locality, climate, nature of standing-crop, etc. 



* Ramann. Runelr, Schellhorn and Krause, " Anzahl u. Bcdeutung dcr 

 nicdercn Organismcn in Waid u. Moorboden. Zeitschrift f. F. u. Jagdwesen," 

 1889. 



