500 Bulletin 315 



diameter, distended with gelatin, at length on drying becoming condensed; 

 conidia light green, oblong or ovoid, 6-7 by 3-5^- 



Hab. Isolated from humous soil from forest of Spanderswoud 

 near Bussum, Holland, May, 1901, Koning. 



SUMMARY 



The fungous flora of the soil is taken to consist of obligate saprophytes 

 and facultative parasites. The former are by far the more abundant in 

 the soil. 



Many facultative parasites can be directly isolated from the soil, as 

 shown by the isolation of Colletotrichum sp., Fusariuni sp., Macrosporium 

 sp., Helminthosporium sp., by Beckwith; Pythium de Baryanum Hesse, 

 by Butler; Rhizopus nigricans Ehren., by Hagem and by the writer; 

 Trichoderma Koningi Oud., by Oudemans and by the writer; Trichoderma 

 lignorum (Tode) Harz, Trichothecium rosemn Link, Ftisarium oxyspomm 

 Schlecht. {Fusariuni orthoceras Appel), and Hormodendrum Hordei Bruhne, 

 by the writer. 



Some facultative parasites are very widely distributed, as is shown by 

 the isolation of Rhizopus nigricans Ehren., Trichoderma Koningi Oud., 

 Pythium de Baryanum Hesse. All three species have been isolated in 

 Europe. The first two have been isolated by the writer at Ithaca, N. Y. 

 The last-mentioned species is known to be generally distributed in the 

 United States, although it has not been isolated. 



The isolation of soil fungi, because of specialization as to food, tempera- 

 ture and moisture requirements, and aerobic or anaerobic conditions, 

 requires different technic and media. 



A fungus should not be considered as belonging to the soil flora unless 

 it has been directly isolated or has been shown under control experimen- 

 tation to live in the soil. Control experimentation consists in growing 

 a crop from absolutely clean seed in sterilized and nonsterilized soil, all 

 other conditions being identical. This latter method of proof has shown, 

 so far as the " Wurzelbrand " of sugar beets is concerned, that Phoma 

 Betae Fr. winters on the seed balls and not in the soil, while Pythium de 

 Baryanum Hesse and Aphanomyces laevis de Bary winter as saprophytes 

 in the soil and not on the seed balls. 



The history of the study of the fungous flora of the soil consists of two 

 definite lines of study: one line consists of an isolation of soil forms in 

 order to obtain a knowledge of the forms themselves prior to making 

 biochemical studies, and also to obtain a knowledge of the habitat and the 

 distribution of the species ; the other line consists in obtaining a knowledge 

 as to whether a facultative parasite does or does not live over winter in 

 the soil. 



