68 



THE SOIL POPULATION AND ITS DISTRIBUTION 



seen from Table 12, it is likely that fungi exist in soils in the vege- 

 tative state to a much greater extent than in the form of spores. 

 It has been observed that, when vegetative growth is rapidly- 

 desiccated in soils, it undergoes destruction; under the same con- 

 ditions fungus spores are unaffected. When soils containing the 

 soil organisms in their normal condition are rapidly desiccated, 

 the numbers of fungi are very largely reduced. Therefore, it 

 seems likely that when one counts colonies of fungi on agar plates 

 prepared from soil dilutions, one is counting colonies which have 

 developed from pieces of mycelium of the organisms. What the 

 sizes of the pieces of mycelium may have been at the time of the 

 determination is unknown. Undoubtedly the individual pieces 

 varied greatly in size. 



TABLE 12 



Influence op Desiccation of Soils on Development of Colonies of 

 Fungi on Agar Pl.\tes (from McLennan) 



The value of the plate method for determining the abundance 

 of fungi in the soil is further limited by the fact that many fungi 

 fail to grow on the media commonly used for their determination. 

 In this respect there is a similarity to the plate method for deter- 

 mining the numbers of bacteria. The results of these fungus 

 counts should, therefore, be interpreted only as rough quantitative 

 measurements of certain representatives of the fungus population. 



The types of fungi which are found in different cultivated soils 

 are much the same, but the relative abundance of any of the species 

 is determined by the environmental conditions. One of the most 



