FUNGOUS FLORA OF THE SOIL* 



C. N. Jensen 



For many years the fungous flora of the soil has attracted considerable 

 attention from various points of view. From a purely systematic stand- 

 point, little has been known until recently of the species constituting a 

 part of this flora, and Httle has been known of its biology and physi- 

 ology. The present work is the outcome of investigations begun with a 

 view to determine the extent of distribution of known pathogens in the 

 soil and of their ease of isolation by cultural methods. Hence the 

 systematic study and technic have been emphasized with a view to pav- 

 ing the way for more fertile biological and biochemical studies, as well as 

 to serve as a basis for a monograph of the soil fungi. 



The fungous inhabitants of the soil may properly be classified as obli- 

 gate saprophytes and facultative parasites. In the determination of the 

 obligate saprophytic forms, we must resort to the isolation of the forms 

 by cultural methods only, while the determination of the facultative para- 

 sites may be carried on in two ways: one by isolation, the same as with the 

 obligate saprophytes, and after isolation the determination of the patho- 

 genicity of the form in question by a series of inoculations on the presum- 

 able host; the other, the reciprocal of this, by growing crops under 

 controlled conditions and, in case disease due to parasitic fungi arises, 

 in isolating the causal organism from the host. 



The isolation of fungi from the soil is not so simple a task as at first 

 sight it might appear. While it is true that we must consider the fungous 

 flora of the soil as consisting of saprophytes, it does not follow that all 

 these fungi will yield to one and the same cultural method or that they 

 will grow on similar media. There must be a certain specialization as to 

 food relations, temperature, moisture, oxygen, and so forth, with sapro- 

 phytes as well as with parasites. This specialization must exist a priori 

 in various degrees. 



Every amateur student in mycology or plant pathology knows that 

 if he wishes to collect a Pilobolus, a Sordaria, or a Chaetomium, he is most 

 likely to find it on dung; in order to find Pyronema confluens, he looks for 

 it on burned areas; again, certain saprophytes, such as the Cytosporas, 

 grow commonly on dead twigs of the stone fruits, Salix, Populus, and the 

 like. This specialization is recognized well in classification, as we often 

 find groups of fungi designated by such words as fimicole, lignicole, cauli- 

 cole, and so on. This being accepted without question, how readily 



♦Also presented before the Faculty of the Graduate School of Cornell University January 19, 1912, 

 ^ a major thesis in partial fulfillment of the requirements for the degree of Doctor of Philosophy. 



415 



