NUMBERS OF MICROORGANISMS 



43 



ing on the plate are due to spores and how many to pieces of mycelium. 

 There is also no basis for comparing the relative abundance and potential 

 activity between the bacterial and fungus flora of the soil; for example, 

 1000 colonies of fungi may indicate a greater activity than 1,000,000 

 colonies of bacteria, when a certain process, such as cellulose or protein 

 decomposition is studied. However, if the 1000 fungus colonies repre- 

 sent inactive spores, the activity of the organism may be questioned. 

 With these limitations in mind and in view of the fact that most of the 

 determinations of numbers of fungi have been made by the use of high 



Nwi4- Dec I Dec 19 Jan 7 Jon 23 Febu Feb 29 Mar^i Aprs April 



Fig. 4. Variation of numbers of fungi at different seasons of the year and 

 different depths of soil (from Loehhead). 



dilutions and of the bacterial agar plate, it is questionable to what extent 

 many of the results obtained in the past actually represent even relative 

 soil conditions. In general, the soil is found 98 to harbor between 30,000 

 and 900,000 fungi (spores and pieces of mycelium) per gram, depending 

 on the type of soil and treatment. Others" reported a range of 42,000 



98 Waksman, S. A. Soil fungi and their activities. Soil Sci. 2: 103-155. 

 1916; Is there any fungus flora of the soil? Ibid. 3: 565-5S9. 1917; Waksman, 

 S. A. Influence of soil reaction upon the distribution of fungi in the soil. Ecol- 

 ogy, 6: 54-59. 1924. 



89 Brown and Halversen. 1919 (p. 33). 



