14 



CLASS BASIDIOMYCETEAE: SUBCLASS 

 EUBASIDIAE, "HYMENOMYCETEAE" 



Subclass Eubasidiae 



IN CONTRAST with the Heterobasidiae the Eubasidiae possess basidia 

 which are one-celled and which mostly do not show a sharp distinction 

 into hypobasidium and epibasidium. The nuclear divisions occur in the 

 body of the basidium and after the spores have arisen at the ends of true 

 sterigmata the nuclei pass through the latter into the spores. The nuclear 

 spindles may be parallel to the longitudinal axis of the basidium (sticho- 

 basidial) or at right angles to this axis (chiastobasidial). In a few species 

 both types of basidia may be present (Exobasidium and some Boletaceae). 



In the genera included in the "Hymenomyceteae" the basidia occur 

 in a hymenium (in a few species they are scattered so that no continuous 

 hymenium is present), which becomes exposed to the air before the spores 

 are shot off from the sterigmata to whose tips they are obliquely attached. 

 These characters are in contrast to the situation in the group of orders 

 to which collectively the name " Gasteromyceteae " has been applied (see 

 next chapter). In these the spores are mostly attached symmetrically to 

 the tips of the sterigmata and are not thrown off. They are set free by the 

 opening of the basidiocarps to the air in various manners after the spores 

 are mature. 



The fungi included as Hymenomycetes have been considered to form 

 one order, Agaricales; or two orders, Polyporales (or Aphyllophorales) 

 and Agaricales, or several orders (Heim, 1934). In the main two series 

 can be distinguished; those in which the basidia so far as studied are 

 stichobasidial (most of the Polyporales) and those in which the nuclear 

 division where investigated has been shown to be chiastic (Agaricales). 

 It must be noted that of the thousands of species in this subclass only a 

 few in each group have been studied cytologically. 



It is not by any means settled whether the families considered to be- 

 long to this subclass really form a monophyletic series or whether some of 



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