SOIL ORGANISMS 389 



in the surface soil. While the microscopic algae are probably- 

 present in soils, it has never been shown that they are of 

 practical importance. 



213. Actinomyces. — The actinomyces are a filamentous 

 form of organisms, widely distributed in nature and are prob- 

 ably more nearly related to the bacteria than to the molds, 

 although they produce spores and develop into branching 

 forms of considerable complexity. Their production of aerial 

 hyphae is quite unlike the habits of bacteria. These thread 

 organisms exist in the soil in both the vegetative and the 

 resting stage and often make up quite a large proportion of 

 the soil flora. They are extremely difficult to study, since 

 they produce hard compact growths. It is questionable also, 

 whether the growths produced artificially are exactly like 

 those occurring in the soil. 



Hiltner and Stormer * found that 20 per cent, of the soil 

 organisms developing on gelatin plates inoculated from the 

 soil were actinomyces. Conn 2 reports a range from 11 to 75 

 per cent, under similar cultural conditions. The average was 

 38 per cent. Conn estimates that 20 per cent, of the average 

 flora consists of actinomyces. The organisms were generally 

 greater in meadow soil than in cultivated land, indicating 

 the relationship of these thread forms to cellulose decomposi- 

 tion. McBeth 3 found actinomyces of wide distribution in 

 soils and he concludes that they are undoubtedly an impor- 

 tant factor in the decomposition of the cellulose of the soil 

 organic matter. 



1 Hiltner, L., and Stormer, K., Studien uber die Bdkterienflora des 

 Ackerbodens ; Kaiserliches Gesundheitsamt, Biol. Abt. Land-u. Forstw., 

 Bd. 3, S. 445-545, 1903. 



2 Conn, H. J., A Possible Function of Actinomycetes in Soil; Jour. 

 Bact., Vol. 1, No. 2, pp. 197-207, 1916. 



3 McBeth, I. G., Studies on the Decomposition of Cellulose in Soils; 

 Soil Sci., Vol. I, No. 5, pp. 437-487, 1916. Also, 



Waksman, S. A., and Curtis, R. E., The Actinomyces of the Soil; 

 Soil Sci., Vol. 1, No. 2, pp. 99-134, 1916. 



Waksman, S. A., Cultural Studies of Species of Actinomyces; Soil 

 Sci., Vol. VIII, No. 2, pp. 71-207, 1919. 



