INTRODUCTION xi 



parasites dependent on a living host. Sometimes the mycelium 

 forms a somewhat dense stratum (stroma) on which the receptacle 

 is seated or immersed; at other times it forms hard compact 

 masses known as sclerotia which often lie dormant for a con- 

 siderable length of time. 



In more recent classifications the BASIDIOMYCETAE are 

 primarily divided into two main divisions, the HOMOBASIDIAE 

 and the HETEROBASIDIAE. In the former, the basidium is an 

 undivided cell usually clavate in shape: the spores on germina- 

 tion give rise to a mycelium which reproduces the sporophore. 

 In the latter, the basidia are either transversely, longitudinally, 

 or vertically septate, or sometimes continuous, but the spores on 

 germination give rise to sporidiola which germinate in their turn 

 to form the mycelium which reproduces the fruit body. 



The HOMOBASIDIAE are divided into two main subdivisions 

 based upon their parasitic or saprophytic habit. The parasitic 

 forms constitute the subdivision EXOBASIDIINEAE, the sapro- 

 phytic forms the subdivision EU-HOMOBASIDIINEAE. The latter 

 are divided into the three orders Gasteromycetales, Agaricales and 

 Aphyllophorales. 



The Gasteromycetales include the species having the hymenium 

 still surrounded at maturity by a peridium: the Agaricales have 

 the hymenium originally protected by a volva or a ring but at 

 maturity fully exposed, whilst the Aphyllophorales have the 

 hymenium exposed from the first. 



The HETEROBASIDIAE are divided into four orders according 

 to the nature of the basidium, viz. Auriculariales, Tremellales, 

 Tulasnellales and Calocerales. In the Auriculariales the basidia 

 are transversely septate; in the Tremellales the basidia are 

 longitudinally, cruciately divided; the Tulasnellales have simple 

 basidia but the sterigmata are at first of such a wide diameter 

 that they were formerly considered to be spores, whilst the 

 Calocerales have cylindrical basidia terminated by two pointed, 

 usually long, sterigmata. All these orders are in general sapro- 

 phytic and have the hymenium fully exposed from the first but 

 the Auriculariales include the three parasitic suborders Puc- 

 ciniineae, Coleosporiineae and Ustilagineae which are not dealt 

 with in the present work and one suborder the Ecchynineae 

 which has the hymenium inclosed within a peridium at maturity. 



