SOIL FUNGI 271 



ing to the genus Phoma (P. betae 132 and P. radicis m ), where positive 

 nitrogen fixation has been demonstrated. Nitrogen fixation by yeasts 

 was also found to be negative. 135 A detailed review of the literature 

 on nitrogen fixation by fungi (and algae) is given by Czapek. 136 The 

 possibility that certain fungi, like Pen. luteum, are capable of oxidizing 

 sulfur has also been suggested. 137 ' 138 



MYCORRHIZA FUNGI 



Nature of mycorrhiza formation. Pfeffer 139 was the first to call atten- 

 tion to the possible symbiotic action between the roots of plants and 

 fungi. The roots of higher plants, especially trees, were found to be 

 commonly interwoven with fungus mycelium to form a symbiotic 

 growth, to which the term "mycorrhiza" was applied. 140 These forma- 

 tions were found to be abundant in humus or other soils containing 

 undecomposed plant residues. Frank divided the mycorrhiza into 

 two groups: 1. Ectotrophic mycorrhiza, when the fungus produces an 

 external investment of the root, in the form of a crown of hyphae, 

 without penetrating into cells other than those of the epidermis. There 

 is an extensive intercellular development between the cortical cells 

 of the root. This is especially characteristic of forest trees. 2. Endo- 

 tro'phic mycorrhiza, in which the hyphae of the fungus penetrate to 

 the inner parts of the roots, into definite root layers and into the cells. 

 This is true of the Orchidaceae, Ericaceae and Eparidaceae; however, 



134 Ternetz, C. Uber die Assimilation des atmospherischen Stickstoffs durch 

 Pilze. Jahrb. wiss. Bot., 44: 353-408. 1907. 



136 Kossowicz, A. Zur Frage der Assimilation des elementarem Stickstoffs 

 durch Hefen und Schimmelpilzen. Biochem. Ztschr., 64: 82. 1914. 



1,6 Czapek, 2: 192-198, 1920 (p. xv). 



137 Abbott, E. V. The occurrence and action of fungi in the soil. Soil Sci., 

 16: 207-216. 1923. 



138 Rippel, A. tjber einige Fragen der Oxydation des elementaren Schwefels. 

 Centrbl. Bakt. II, 62: 290-295. 1924. 



139 Pfeffer, W. tlber fleischfressende Pflanzen und iiber die Erniihrung durch 

 Aufnahme organischer Stoffe iiberhaupt. Landw. Jahrb., 6: 969-99S. 1S77. 



140 Frank, B. Uber die auf Wurzelsymbiose beruhende Ernahrung ge- 

 vvisser Baume durch untererdische Pilze, und neue Mitteilungen iiber die Mykor- 

 rhiza der Biiume und der Monolropha hypopihjs. Ber. deut. bot. Gesell., 3: 

 143, XXVII. 1885; Uber neue Mykorrhiza Formen. Ibid., 5: 395-408. 1887; 

 Uber die Verdauung von Pilzen abzielende Symbiose der mit endotrophen My- 

 korrhizen begatteten Pflanzen. Ibid., 9: 244. 1891. 



