388 



FUNGI 



Class XXII.— Basidiomycetes. 



The Basidiomycetes are a large class comprising forms of the utmost 

 diversity in appearance, mostly saprophytes living on humus, rotten wood, 

 or the old wood and the bark of trees. A small number are parasites. 

 They all agree in the production of spores {pasidiospores) acrogenously 

 on basids, which are club-shaped and disposed as a rule parallel to each 

 other^ thus forming hymenia. The spores produced on one basid are 

 two or four in number, more rarely eight, though divergences from these 

 numbers occur. They vary in shape, but consist, except in some Tremel- 

 linese, of a single cell. Among the basids there commonly occur sterile 

 hyphal branches — paraphyses. Besides these spores thus borne on 

 definite hymenia there are also others produced more or less inde- 

 finitely on the myceles of certain members of the group, and their 

 character will be described below. The Basidiomycetes are divided 

 into two sub-classes, the Hymenomycetes with gymnocarpous, and the 

 Gasteromycetes with angiocarpous fructification. 



Sub-class 1. — Hymenomycetes. 



The Hymenomj-cetes are characterised by the possession of a 

 hymenium on the free exposed surface of the compound structure which 

 bears it — the sporophore. The forms embraced in this sub-class range 

 from very simple to highly complex structures, the latter being repre? 



Fig. ■ixd.—Tremella mesenterica Retz. (natural size). (After Tula.sne.) 



sented by such types as the common mushroom and the like — in short 

 those fungi to which the name is popularly applied. 



ExoBASiDiUM Vaccinii (Woron.) may be taken as the simplest type. 

 Its mycele is parasitic on the leaves and stems of Vaccinium vitis-idaea, 



