NATURE OF SOIL MICROBES 



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soil discloses a heterogeneous assortment of forms belonging to no 

 single classified group, either physiologically or morphologically. 

 They vary considerably both in their general appearance and in 

 the nature of the processes which they bring about. The indi- 

 vidual organisms are so small that they cannot be seen with the 

 naked eye and their structures can be studied only by means of 

 powerful microscopes. However, a mass of growth of micro- 

 organisms, frequently referred to as a colony, can be obtained on 



Fig. 8. — Aerobic cellulose-decom- 

 posing bacterium, Cytophaga lutea 

 (from Winogradsky). 



Fig. 9. — Anaerobic, cellulose-decom- 

 posing bacterium, Bacillus cellulosae 

 dissolvent (from Khouvine). 



natural or artificial substrates, large enough to be studied with 

 the naked eye. 



Nature of Soil Microbes. — Both in respect to numbers and 

 abundance of cell substance in the soil, most of the microbes 

 belong to the plant kingdom. These include various bacteria, 

 actinomyces or ray fungi, a number of true fungi including the 

 molds and the mushrooms, as well as various green and blue-green 

 chlorophyll-bearing algae. The animal kingdom is numerically 

 less abundant in the soil. Representatives include the protozoa, 

 the nematodes or round-worms, the rotarians or wheel animal- 

 cules, a number of earthworms, and larvae of insects. In view of 

 the fact that, in the case of some microbes, it is difficult to decide 

 whether they should be classified with plants or with animals, 



