184 THE LURE OF THE LAND 



THE ROLE OF BACTERIA. 



" The intimate relations which have been found to 

 subsist between certain minute organisms and the chem- 

 ical reactions which take place in the soil is a sufficient 

 excuse for noting the effect of other similar organisms 

 in the formation of soils. 



" In addition to the usual forces active in decompos- 

 ing rocks Miintz has described the effects of a nitrifying 

 bacillus contributing to the same purpose. 



" According to him the bare rock usually furnishes a 

 purely mineral environment where organisms cannot be 

 developed unless they are able to draw their nourish- 

 ment directly from the air. Some nitrifying organ- 

 isms belong to this class. It has been shown that these 

 bodies can be developed by absorbing from the ambient 

 atmosphere carbonate of ammonia and vapors of alco- 

 hol, the presence of which has been observed in the air. 

 According to the observations of Winogradsky, they 

 assimilate even the carbon of the carbon dioxid just as 

 the parts of plants which contain chlorophyl. Thus 

 even on the denuded rocks of high mountains the con- 

 ditions for the development of all these inferior organ- 

 isms exist. In examining the particles produced by 

 attrition, it is easily established that they are uniformly 

 covered by a layer of organic matter evidently formed 

 by microscopic vegetation. Thus we see, in the very 

 first products of attrition, appearing upon the rocky 

 particles the characteristic element of vegetable soil, 

 viz., humus, the proportion of which increases rapidly 

 with the products of disaggregation collected at the foot 

 of declivities until finally they become covered with 

 chlorophyliferous plants. 



" In a similar manner the presence of nitrifying or- 



