The Concept of Soil Microbiology 5 



From the point of \'icw of their economic value, the nmnerous soil- 

 inhabiting microorganisms include forms which are useful and highly 

 important for plant and animal life; these take part in the decomposi- 

 tion of organic residues and in the liberation of the nutrient elements 



Fig. 2. Sir Henry Gilbert, the first chemist of the Rothamsted Experimental 



Station. 



in available forms, as well as in numerous other transformations of 

 various elements and compounds which are essential for the con- 

 tinuation of life on this planet. Other groups of soil-inhabiting 

 microorganisms include other forms of economic importance which 

 are injurious to plant and animal life; this effect may either be direct, 

 by attacking and destroying the higher forms of life, or indirect, by 

 transforming certain chemical compounds into substances injurious 

 to living processes. Here belong the numerous plant and animal 

 pathogens that find in the soil a permanent or temporary habitat. 



