ORDER TREMELLALES 453 



to the similar structures growing out of the cells of the basidia of Auricu- 

 laria and cannot rightly be called epibasidia, for the epibasidia of Auricu- 

 lariales and the promycelium of Uredinales are probably homologous, but 

 are entirely different from these tubular extensions to bring the spore pro- 

 duction to the surface. The basidiospores are hyaline or only slightly 

 colored. They are without septa when set free. They may then become 

 once septate, but more often not. Frequently they produce a sterigma and 

 a secondary spore, a process several times repeated. In abundance of 

 moisture the spores bud out innumerable "oidia" on their surface. They 

 may, if on a proper substratum, germinate by hyphae. The primary 

 mycelium produces an abundance of oidia and lacks clamp connections. 

 Eventually clamp connections appear (secondary mycelium) and oidial 

 production usually ceases. Barnett (1937) showed for several species of 

 Exidia that the spores from a given spore fruit exist in two sexual phases. 

 Multiple allelomorphy of the compatibility factors was demonstrated 

 also, as occurs in Auricularia and in various Ustilaginales. 



Over 100 species in 17 or more genera are recognized in this order, of 

 which about half are found in the North Central United States and 

 Canada (Martin, 1944). 



Three families are usually distinguished: 



Family Tremellaceae. Basidia are single and terminal on the sup- 

 porting hyphae, with a more or less elongated extension from each cell, 

 terminated by a sterigma. They are gelatinous, waxy or somewhat dry. 

 Basidia normally are cruciately four-celled but sometimes three-celled 

 or even two-celled. The primary septum is vertical or oblique. Hymenial 

 surface is exposed. Spore fruits may be flat, cushion-shaped, lobed, or 

 pileate. Clamp connections present in secondary mycelium of many 

 species. (Fig. 149.) 



Family Sirobasidiaceae. Gelatinous, cushion-shaped, hymenium ex- 

 ternal. Basidia are formed in chains by successive transformation of the 

 cells of the basidiogenous hyphae into basidia, beginning at the apex. 

 Basidia are four- or two-celled, the septum in the latter case oblique. Ba- 

 sidiospores are sessile and therefore probably not discharged violently. 

 Mostly tropical but known in the United States from North Carolina. 

 Contains a single genus, Sirobasidium. (Fig. 150.) 



Family Hyaloriaceae. Spore fruits are stalked, with a head; stalk 

 and head somewhat gelatinous externally or sessile, forming a filmy layer 

 on the substratum. Basidia are two- to four-celled with tubular extensions 

 which may taper to a long fine thread, the basidiospore being borne sym- 

 metrically at the apex and breaking off with part of the supporting thread 

 attached, not discharged from a sterigma. Clamp connections are present. 

 There are two genera : Hyaloria, with one tropical species, H. pilacre A. 

 Moll, (see Martin, 1937b), and one European one, H. europaea Killer- 



