BASIDIOMYCETES 



445 



cally from the lower surface, are thus freely exposed. It is upon the 

 gills that the hymenial layer, bearing the basidia, is borne. The colour 

 of the gills is at first pink, but it gradually grows dark brown with age. 

 This is due to the colour of the spores (basidiospores) produced in large 

 numbers all over its surface. If a young expanded pileus be laid 



Fig. 345. 

 Coprinus sterquilinus. Section through a gill, showing hymenium (hym), subhymenial 

 layer (sub), and trama (tr) ; the basidia {b), each bearing four basidiospores, or only the 

 sterigmata (st), from which the spores have been already thrown off. (After Buller.) 



face downwards upon a sheet of paper, after a few hours a print of 

 the gills will have been traced by the deposit of their spores. 



A vertical section through the gills shows that they consist of a 

 rather lax central region, which supports the more compact hymenium 

 that completely covers their surface (Figs. 344, 345). It is composed 

 of narrow paraphyses which surround the more bulky basidia, the 

 ends of which project, and in the Mushroom bear each two sterigmata, 

 with a basidiospore on the end of each. The number two is, however, 

 exceptional among Basidiomycetes. The basidia of the Honey- 

 Agaric, or of Coprinus, are typical (see Fig. 345)- There the fusion- 

 nucleus divides into four, four sterigmata are formed, and one of the 

 nuclei squeezes through the narrow channel into the basidiospore 

 which each sterigma bears. 



