458 CLASS BASIDIOMYCETEAE 



septum. Each epibasidium produces a terminal sterigma and basidio- 

 spore. The nucleus may divide within the epibasidium and both nuclei 

 pass into the basidiospore. By producing but two epibasidia,not sepa- 

 rated by septa from the hypobasidium the typical tuning-fork basidium 

 of the Dacrymycetales can be evolved. By crowding the basal septa 

 down into the hypobasidium so as to divide that longitudinally into four 

 cells the basidium of the Tremellales may be derived. By reduction of the 

 size of the epibasidia until only the sterigmata are left, is developed the 

 basidium characteristic of the Hymenomycetes. Rogers attempts to ex- 

 plain the derivation of the hypobasidium and single, transversely septate 

 epibasidium of Septobasidivm and of the corresponding teliospore and 

 promycelium of the Uredinales and Ustilaginales as being due to the 

 delay in the meiotic division of the fusion nucleus until it passes out into 

 an epibasidium which naturally would be single for a single nucleus. He 

 believes that the hypobasidium of Tulasnella represents an ascus, perhaps 

 of some form resembling Ascocorticium (Order Taphrinales), in which the 

 ascospores have pushed out into pockets, germinating there to form 

 secondary spores. These pockets have become the epibasidia and the 

 secondary spores have become the basidiospores. Martin (1938) discusses 

 the morphology of the basidium in connection with Heterobasidiae and 

 Eubasidiae. 



Linder (1940) would, on the other hand, derive the Uredinales from 

 the Ascomyceteae, in the vicinity of the Sphaeriales or Dothideales. 

 From the Uredinales he would derive the Auriculariales, Tremellales and 

 Dacrymycetales. The Corticiae (Family Thelephoraceae), and thence the 

 other Eubasidial families he would derive from the Tremellales. 



On the other hand some students of these fungi consider the primitive 

 basidium to have been of the holobasidium type from which the forked 

 and septate types have been derived. The distinction of hypobasidium 

 and epibasidium are, in this viewpoint, specializations to meet the need 

 of holding the basidium over until a more favorable period. The thick- 

 walled hypobasidium (or "probasidium") such as is found in the Telio- 

 sporeae or in Septohasidium cannot, because of the thickened wall, 

 develop in the manner normal to basidia, and so a thin-walled new struc- 

 ture, the epibasidium or promycelium, was developed. The thickened 

 apical branches of the basidia of the Tremellales and Dacrymycetales and 

 of Tulasnella are not considered to be epibasidia but merely modified 

 sterigmata. 



Key to the Families and More Important Genera of Order Auriculariales 



(Modified from Martin, 1944) 



Parasitic on plants or saprophytic on dead plant material, usually wood. Basidia 

 with distinct sterigmata. Division into hypobasidium and epibasidium 



1 



