276 PRINCIPLES OF SOIL MICROBIOLOGY 



lation into a pure culture seedling growing under controlled conditions 

 with subsequent production of mycorrhiza. In the extensive literature 

 on mycorrhiza formation, very few attempts which have been made to 

 isolate the causative organism and cultivate it in pure culture, or to pro- 

 duce mycorrhiza artificially, have proved successful. This has been 

 accomplished in the case of various orchids, 153 in Calluna vulgaris, 154 and 

 especially by Melin for various pine trees. Bernard 155 classified the 

 fungus of orchids with Rhizoctonia, on the basis of sclerotia formation. 

 Burgeff , however, later termed this organism Orcheomyces. 



The organism isolated from Calluna vulgaris was placed by Rayner in 

 the genus Phoma among the Sphaeropsidales. Various members of 

 the genera Cortinarius (between C. rubipes, on the one hand, and 

 Quercus rubra, Picea rubra, or Acer saccharum on the other), Russula 

 (between R. emetica and Quercus rubra), Tricholoma (B. speciosus or 

 T. transmutans and Quercus nigra), Armillaria (A. mellea and the 

 orchid Gastrodia elata), Boletus (Boletus species and pine trees) were 

 found 157-160 to be the causative agents of mycorrhiza formation. 



The true mycorrhiza fungi of forest trees should be looked for largely 

 among the Hymenomycetes, given above. 156 Mycorrhiza formation 

 by Gasteromycetes is still questionable; the same is true of the asco- 

 mycetes, although Rhizoctonia belongs to this group. A number of 

 Hyphomycetes are capable of entering the roots, where they seem to grow 

 more or less parasitically. Some of the Hymenomycetes, such as 

 Boletus elegans, are highly specialized upon certain host plants, whereas 

 some are less specialized, such as Amanita muscaria, which are capable 

 of forming mycorrhiza with species belonging to various genera. 



163 Bernard, 1909 (p. 272); Burgeff, H. Die Anzucht tropischer Orchideen 

 aus Sarnen. Jena. 1911; Die Wurzelpilze der Orchideen. Jena. 1909;Schatz. 

 Beitrage zur Biologie der Mykorrhizen. Inaug. Diss. Jena. 1910. 



164 Rayner, 1915~(p. 274). 

 166 Bernard, 1909 (p. 272). 



166 Melin, E. Untersuchungen iiber die Bedeutung der Baummykorrhiza. 

 Langmenska Kulturf. G. Fischer. 1925. Jena. 



167 Kauffman, C. H. Cortinarius as a mycorrhiza-producing fungus. Bot. 

 Gaz., 42: 208-214. 1906. 



158 Pennington, L. H. Mycorrhiza-producing Basidiomycetes. Rpt. Mich. 

 Acad. Sci., 10: 47. 1910. 



169 Rommel, L. G. Parallelvorkommen gewisser Boleten und Nadelbaume. 

 Svensk. Bot. Tidskr., 15: 204-213. 1921. 



160 Melin, E. tJber die Mykorrhizenpilze von Pinus silvestris L. und Picea 

 abies (L.). Karst. Svensk. Bot. Tidskr., 15: 192-203. 1921; Jour. Ecol., 9: 

 254-257. 1922. 



