HYMENOMYCETES 355 



highly evolved forms are tropical. Species of Coniophora, 

 Corticiuni) Stereum, etc., form extended crusts on trunks, 

 logs, posts, etc. 



Two genera, Cora and Rhipidoncma> at one time 

 included in the present family, are now known to be 

 lichens, and constitute the group known as Basidio-lichens, 

 on account of the fungal element belonging to the Basidio- 

 mycetes. Both are tropical genera, having a semicircular 

 or fan-shaped pileus attached laterally, and would have 

 been species of Stereum but for the presence of an algal 

 element in the pileus. 



Hydneae 



On this family the hymenium is borne on spine-like 

 processes crowded together, taking the place of tubes in 

 the Polyporaceae, and gills in the Agaricineae. In 

 Hydnum^ the central and most highly evolved genus in the 

 family, the spines are densely crowded, and in some species 

 from two to three centimetres in length. In the genus 

 Phkbia, which forms a bridge from the Thelophoreae to 

 the present family, the hymenial surface is simply rugulose, 

 the edge of the wrinkles being vaguely corrugated or 

 toothed ; in Irpex the teeth or spines are more pronounced, 

 but still originate from anastomosing folds or ridges. 

 Radulum^ with coarse, irregular, subcylindrical but obtuse 

 teeth or spines, leads up to Hydnum. In Odontia the 

 spines are reduced to mere projecting granules, having the 

 tips fringed or minutely fimbriate. The conception of the 

 hymenium being borne on spines, although affording a con- 

 siderable amount of surface at the cost of a small amount 

 of material, has not been extended beyond the Hydnaceae, 

 which thus may be looked upon as a terminal group. 



