CHAPTER XI 



Soil Fungi 



Occurrence of fungi in the soil. The chlorophyll-free microscopic 

 plants are divided into slime-molds (Myxomycetes) , bacteria (Schizo- 

 mycetes or fission fungi) and true fungi {Eumycetes) . The slime-molds 

 are characterized by the formation of a Plasmodium, as a result of 

 fusion of separate individuals. They have been studied only to a very 

 limited extent from the point of view of their occurrence and activities 

 in the soil. All the available information is either limited to the forms 

 occurring on decomposing wood or to those causing plant diseases. 

 Forms like potato wart (Synchitrium endobioticum) or the club- root of 

 cabbage and other cruciferae (Plasmodiophora brassicae) once intro- 

 duced into the soil persist there for a considerable period of time. How- 

 ever, little is known concerning their role in soil processes. 



The Eumycetes or true fungi cannot derive their energy from the 

 oxidation of inorganic substances; they are heterotrophic, depending 

 for their energy supply on the decomposition of plant and animal sub- 

 stances; their existence in the soil is thus closely connected with the 

 decomposition of the organic matter added to the soil. Two distinct 

 groups of fungi are found in the soil: (1) the ordinary filamentous 

 fungi or molds, living freely in the soil, and (2) those capable of forming 

 mycorrhiza with higher plants. The higher or mushroom fungi are 

 found both among the free living forms and among those forming 

 mycorrhiza. The soil also harbors various fungi capable of causing 

 plant diseases, which are considered in detail elsewhere (p. 801). 



It has been known for some time that fungi occur abundantly in the 

 soil, particularly in soils rich in organic matter and acid in reaction. 

 But in view of the fact that fungi are present in the soil both in the 

 form of vegetative mycelium and as reproductive spores, it is rather 

 difficult to estimate their abundance; it is even less possible to find a 

 basis for comparing the relative abundance of fungi and bacteria in 

 the soil and their capacity for causing a certain amount of transfor- 

 mation in the soil. It has been recognized 1 that, under certain condi- 



1 Moore, G. J. Microorganisms of the soil. Science, 36: 609-615. 1912. 



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