Distribution of Nonbacterial Microorganisms 



55 



far greater degree of potential acti\ity than the presence of a mil- 

 Hon bacteria. This is particularly true when a certain process, such 

 as cellulose or protein decomposition, is stndied. If the number of 

 fungus colonies is a result of de\'elopment of inactive spores, the 

 significance of such a comparison may be further questioned. 



Among the factors which control the abundance of fungi in the 

 soil, the reaction occupies a prominent place. An acid medium, ad- 



40,000 



15 22 29 5 12 19 26 3 

 October November 



10 17 24 31 

 December 



Fig. 



7 14 21 28 

 January 



26. Changes in numbers of bacteria and flagellates in soil (from Cutler 

 and Crump). 



justed to ;jH 4.0, is frequently used for determining the numbers 

 of fungi in soil, since at that reaction most of the bacteria are elim- 

 inated. This reaction is not the optimum for the growth of fungi, 

 which lies rather at pH 4.5-5.5. As the acidity of the soil decreases, 

 the number of fungi decreases and the actinomycetes and bacteria 

 increase. 



Singh found a direct correlation between soil fertility and the 

 number of fungi and actinomycetes in the permanent mangel and 

 wheat fields at Rothamsted. The evidence concerning the periodic- 

 ity of these organisms was inconclusi\e, the numbers being usually 

 lower in winter. The nature of the crop did not exert a dominant 

 eflfect, the actinomycetes being relatively higher in the wheat fields 

 and the fungi in the mangel fields. 



Protozoa are also abundant in the soil, their numbers and distri- 

 bution being influenced greatly by the soil and environmental fac- 



