HYMENOMYCETES 



359 



distinctly marked structural zones or layers. A central 

 portion, called the trama, consists of more or less parallel 

 hyphae continuous with the hyphae of the pileus. The 

 trama is bounded on either side by a densely interwoven 

 layer, the subhymenial layer, the hyphae of which give 

 origin to the basidia and paraphyses, whose free tips form 

 the surface of the lamella or gill. Cystidia originate from 

 the hyphae of the trama, and not from those forming 

 the subhymenial layer. In the genus Sckizophyllum the 

 free margin of the gill is split along the line of the trama for 

 a very short distance inwards, the split halves respectively 

 curling outwards or away from the split. A much slighter 

 groove runs along the edge of the gill in the genus Trogia. 

 In other genera the edge of the gill is entire and thin. In 

 many species the gills are connected by ridges which 

 spring from the substance of the pileus, but such connect- 

 ing ridges are much shallower than the depths of the gills 

 themselves. 



In one genus, Montagnites^ the pileus or upper sterile 

 protective portion of the sporophore is entirely absent, the 

 gills originate from the apical portion of the stem, and 

 radiate like ordinary gills, but without any supporting 

 membrane above. This genus is a native of the Egyptian 

 desert, and the entire sporophore is at first enclosed in 

 a volva buried in the sand ; in this position the whole of 

 its development takes place, and when the spores are ripe 

 the volva is ruptured and the sporophore raised into the 

 air on a tall stem. In all other genera the gills are attached 

 throughout their length to the under surface of the pileus 

 from which they originate. On the other hand, the 

 relative amount of attachment, or entire freedom of the 

 gills from the stem, is a matter of importance from a 



