200 THE LURE OF THE LAND 



est profusion and do not include all which are now con- 

 tributing to increase the store of vegetable debris. 



NATURE. OF HUMUS. 



The active principle of vegetable mold is called 

 humus, a term used to designate in general the products 

 of the decomposition of vegetable matter as they are 

 found in soils. In peat and vegetable soils is found a 

 mixture of humus with undecomposed or partially de- 

 composed vegetation. 



According to Kostyschoff vegetable matter decays un- 

 der the influence of molds and bacteria. Molds alone 

 produce the dark colored matters which give soils rich 

 in vegetable matter, their color. One chief character- 

 istic of humus is its richness in nitrogen. Black Russian 

 soil contains from 4 to 6.65 per cent, of nitrogen. This 

 soil is estimated to contain 60,000,000 organisms per 

 gram and much of the nitrogen which it holds must be 

 in the form of proteid derivatives. The first develop- 

 ment in decaying vegetable matter is of bacteria and 

 there is a tendency of the decaying matter to become 

 acid. This causes the death of the bacteria and the 

 ammonia produced thereby neutralizes the acid. The 

 various kinds of mold grow when the reaction becomes 

 neutral. Afterwards the bacteria and the molds de- 

 velop together. This statement of Kostyschoff is not a 

 very satisfactory explanation of even our limited knowl- 

 edge of the decomposition of organic matters in the 

 soil. Ammonia and ammonia salts are formed not by 

 the decay of some forms of bacteria but by the activi- 

 ties of other forms. It has been found that in nitri- 

 fication there are three distinct forms of bacteria con- 

 cerned in the final products of ammonia, nitrites, and 

 nitrates. Humus always contains easily decomposable 



