292 THE BASIDIOMYCETES 



basidium is differentiated into a swollen hypobasidium (proba- 

 sidium) and a transversely septate epibasidium; in other forms 

 a hypobasidium is lacking, and the basidium itself is transversely 

 septate. It will be recalled that basidia of the transversely sep- 

 tate type are also found among the Uredinales, from which the 

 Auriculariales have probably been derived. In the Auriculariales, 

 however, many species are saprophytic, although a few are obli- 

 gate parasites, and they do not possess numerous spore forms 

 characteristic of the rusts. 



The Auriculariales, including some 15 genera and approxi- 

 mately 250 species, are customarily divided into 3 families. The 

 Auriculariaceae include both parasitic and saprophytic forms in 

 which the development is gymnocarpous. Certain gymnocarpous 

 members of the order are placed in the family Phleogenaceae, 

 however, and the Septobasidiaceae comprise a number of species 

 characterized in nature by a peculiar biological association with 

 scale insects (coccids). 



Auriculariaceae. The Auriculariaceae, with the majority of 

 the genera, include only gymnocarpous forms, some of which 

 have basidia borne directly on the mycelium and others of which 

 have large and complex fruiting bodies. 



The imperfect fungus Rhizoctonia croconmi is an economically 

 important parasite of clover and potatoes. Its purplish mycelium 

 bears binucleate conidia both in the soil and on the host plant. It 

 has recently been found [Buddin and Wakefield (1927), Ware 

 (1929)] that R. crocorinn has an auriculariaceous perfect stage 

 known as Helicobasidiinn piirpiireinn. The mycelium adjacent 

 to the fructifications is binucleate, and the terminal cells become 

 hypobasidia. The hypobasidium gives rise to a curved 4-celled 

 epibasidium bearing 4 basidiospores. Boedijn and Steinmann 

 (1931), in spite of the presence of a helical epibasidium in some 

 species of Septobasidium as well as in Helicobasidium, and be- 

 cause of the presence of a more expansive and complex fruiting 

 body containing scale insects in Septobasidium, have separated 

 these 2 genera. No such insect relationship is found in Helico- 

 basidium. 



The closely related Genus Cystobasidium [Lagerheim (1898)] 

 is parasitic upon fruiting bodies of the coprophilous discomyce- 

 tous Lasiobolus. In Cystobasidium the hypobasidia become 

 thick-walled, persistent structures, to which the name sclero- 



