432 SOIL FUNGI 



throughout the world, according to Emerson (1941) and Wolf 



(1940. 



Number of fungi in soils and factors influencing preva- 

 lence. The quantitative determinations of fungi in soils have been 

 made by use of dilution-poured plates, and the results obtained do 

 not constitute an entirely satisfactory estimation. Anions the 

 factors that are known to influence the results are: (1) dilution 

 of soil suspension, (2) kind of culture medium, (3) reaction of 

 medium, (4) kind of soil, (5) soil reaction, (6) depth at which 

 sample was taken, (7) moisture, (8) season of the year, (9) till- 

 age, (10) manuring practices. 



If the soil fungi are sporulating in the sample being examined, 

 the number of colonies will be lar^e; if they are merely ves;etatin<j;, 

 the investigator may get a small count and as a result may infer 

 that few fungi are present. 



Data presented by Brierley (1923) show that portions of the 

 same soil suspension plated on different media yield strikingly dif- 

 ferent numbers of colonies! Furthermore, when the same soil 

 suspension is plated on the same medium, adjusted to different 

 initial hydroeen-ion concentrations, the number of colonies de- 

 veloping is very different. Brierley 's observations from monthly 

 plate counts of fungi in soils at the Rothamsted Experiment Sta- 

 tion led him to conclude that there is a seasonal rhythm in the 

 number of soil fungi, ranging from approximately 200,000 to 

 1,600,000 per gram. Jensen (1931), using European soils from 

 fields, meadows, forests, heaths, moors, and marshes, secured 

 counts ranging from 24,300 to 46,000 per gram of soil. 



Accord exists among all investigators that fungi are most abun- 

 dant near the surface of the soil and that the number decreases 

 with depth. LeClerg and Smith (1928) found Aspergillus mger 

 and Trichoderma lignorum in Colorado soils only at the surface. 

 Russell (1923) isolated 30 species at a depth of 1 in. from the 

 surface of an unmanured grass plot, 19 species at 6 in., and 1 1 spe- 

 cies at 12 in. Goddard (1913) in .Michigan and Werkenthin 

 (1916) in Texas found quite the same uniform distribution of 

 species to a depth of approximately 4 in. Waksman (1916) found 

 Z,y gorhynchus vuilleminii most often in subsoil at depths of 12 

 to 20 in. Cobb (1932) recorded that fungi are 10 times as abun- 

 dant in the top soil under hemlock trees as in the subsoil. The 

 data of Takahashi (1919) showed 590,000 fungi per gram of soil 



