388 NATURE AND PROPERTIES OF SOILS 



tance in soils, although it is doubtful whether they are detri- 

 mental except under special conditions. 1 



212. Micro-organisms — fungi and algae. — Of the higher 

 fungi, molds are the only group that apparently attain any 

 particular importance in soils, although yeasts have been found 

 to occur and may in special cases exist in considerable num- 

 bers. It is only recently, however, that fungi have received 

 much attention, although their presence has been noted many 

 times. Such common genera as Fusarium, Mucor, Aspergillas, 

 and Pencillium are usually present in normal soils. In gen- 

 eral, a large amount of organic matter is conducive to the 

 activity of such fungi. Molds occur in soils in both the active 

 and the spore stage and probably pass their various life cycles 

 entirely in the soil. 



Waksman, 2 in a detailed study of soil fungi, found that 

 most of the organisms were capable of producing considerable 

 ammonia from nitrogenous organic matter. A large propor- 

 tion of the fungi isolated were also able to decompose cellulose 

 rather rapidly. Different soils seemed to have a distinct and 

 characteristic fungal flora. Over one hundred distinct species 

 of fungi were isolated by Waksman belonging to thirty-one 

 genera. Some pathogenic species, such as different Fusaria 

 and Alternaria, were found. The numbers ranged from 80,- 

 000 to a gram of soil under forest conditions to 14,000,000 

 to a gram in a meadow soil. The numbers were usually larger 



1 Koch, G. P., Studies on the Activity of Soil Protozoa; Soil Sci., 

 Vol. II, No. 2, pp. 163-181, 1916. 



'Waksman, S. A., Soil Fungi and Their Activities; Soil Sci., Vol. 

 II, No. 2, pp. 103-155, 1916. Also, 



McLean, H. C, and Wilson, G. W., Ammonification Studies with Soil 

 Fungi; N. J. Agr. Exp. Sta., Bui. 270, 1914. 



Kopeloff, N., The Effect of Soil Reaction on Ammonification by 

 Certain Soil Fungi; Soil Sci., Vol. V, No. 1, pp. 541-574, 1916. 



Coleman, D. A., Environmental Factors Influencing the Activity of 

 Soil Fungi; Soil Sci., Vol. V, No. 2, pp. 1-66, 1916. 



Brown, P. E., The Importance of Mold Action in Soil; Science, N. S., 

 Vol. XLVI, No. 1182, pp. 171-175, 1917. 



Conn, H. J., The Microscopic Study of Bacteria and Fungi in Soil; 

 N. Y. State Agr. Exp. Sta., Tech. Bui. 64, 1918. 



