172 



SCIENCE 



[N. S. Vol. XLVI. Nq. ii82 



sey Agricultural Experiment Station,^' *' ° 

 not only furnish a basis upon which future 

 experiments may rest, but they also indicate 

 quite distinctly that the growth of molds 

 in the soil may be of great significance. 



The transformation of organic and inor- 

 ganic compounds in the soil has long been 

 considered the particular function of soil 

 bacteria, but molds may also play an im- 

 portant role in such processes, and indeed 

 it is conceivable that in some instances they 

 may prove largely responsible for the 

 simplification of complex soil materials. 



It is not the purpose of this paper to re- 

 view the previous studies -on molds, for ex- 

 cellent bibliographies have been presented 

 in the work of Waksman* and Coleman- al- 

 ready referred to. It is desired merely to 

 call attention in a brief way to the varied 

 action of molds in soils, and to present a 

 compilation of various published data and 

 some of our own unpublished results along 

 this line, with the idea of emphasizing the 

 need of further study of these organisms. 



In the first place, the number of molds 

 in soils should be considered, and while data 

 along this line are far from conclusive, it 

 has been shown that large numbers of these 

 organisms are always present. Especially is 

 this true for soils rich in humus, and acid in 

 reaction. But the occurrence of fungi is 

 not restricted to such abnormal soils. Neu- 

 tral, well-aerated and well-fertilized soils 

 are also found to contain rich mold floras. 

 Furthermore, fungi are not limited merely 

 to the surface soil, but occur in the deeper 



2 Coleman, D. A., ' ' Environmental Factors In- 

 fluencing the Activity of Soil Fungi," Soil Sci- 

 ence, Vol. II., No. 1, p. 1. 



3 Conn, H. J., ' ' Eelative Importance of Fungi 

 and Bacteria in Soil," Science, N. S., 44, p. 857. 



i Waksman, S. A., ' ' Soil Fungi and Their Ac- 

 tivities, ' ' Soil Science, Vol. II., No. 2, p. 103. 



5 Waksman, S. A., ' ' Do Fungi Actually Live in 

 the Soil and Produce Mycelium?" Science, N. S., 

 44, p. 320. 



soil layers. The well-known predilection of 

 certain fungi for acid conditions has been 

 confirmed and leads to interesting conclu- 

 sions regarding the special importance of 

 these forms in acid soils in which beneficial 

 bacterial action is largely restricted. 



A very important point in connection 

 with the occurrence of molds in soils has 

 been studied recently by Waksman.*^ While 

 the counting methods employed have shown 

 the large numbers of molds in soils, consid- 

 erable doubt existed as to whether these 

 counts represented the actual number of 

 active fungi or only the spores. If spores 

 alone are present, the activity of molds in 

 soils may be of less immediate importance 

 although their presence would indicate pre- 

 vious active growth as well as future activ- 

 ity when the soil conditions become satis- 

 factory for the development of active 

 forms from the spores. Active mold 

 growth on the other hand would undoubt- 

 edly be of immediate importance in the 

 chemical changes occurring in the soil. 

 The value of definite information along this 

 line is apparent. The careful experiments 

 of Waksman show that many molds occur 

 in soils in an active state as well as in the 

 form of spores. While certain groups do 

 not appear to be present in an active con- 

 dition in the soils tested, although the plate 

 method showed their occurrence as spores, 

 studies of other soils may lead to different 

 conclusions. 



Conn^ has attempted to check Waksman 's 

 results by the use of smaller quantities of 

 soil, but was unsuccessful. Using 10 mg. 

 of soil, he secured no growth of mold my- 

 celia such as Waksman obtained with 

 lumps of soil 1 cm. in diameter. He de- 

 scribes a direct microscopic examination of 

 soils and finds no mold mycelia present. 

 He concludes from these experiments that 

 there is serious doubt whether molds exist 

 in soils in an active form iw sufficient num.- 



