EU-MYCETES. (b) BASIDIOMYCETES 



451 



important is the prevention of the manure being contaminated by 

 the carpospores from the smutted crop of a previous year. 



HYMENOMYCETES. 



The Life-His-tory of the Rust of Wheat has been described in some 

 detail as giving an example of a Basidiomycete which still shows 

 evidence of sexuality, both morphologically and physiologically : 



FIG. 386. 



Polyporus igniarius. Section through an old fructification, showing annual zones 

 of growth, a = point of attachment upon the tree which is its host. The porous ' 

 hymenium is directed downwards. ( nat. size.) (From Strasburger.) 



though it is altered from what was probably its normal and original 

 course. In the rest of the Basidiomycetes such evidence is wanting. 

 They may provisionally be held to be saprophytes and parasites 

 which were descended from an ancestry 

 with normal sexuality, but have ad- 

 vanced further in the elimination of 

 their sexual process. The Basidio- 

 mycetes are characterised by their 

 basidia (Fig. 374, p. 441) borne on 

 fruit-bodies which are often large, of 

 various form and brightly coloured. 

 These are produced upon a mycelium, 

 which acquires the necessary nourish- 

 ment sometimes parasitically, but 

 more commonly from saprophytic 

 sources. The basidia are borne in 

 various ways, and this gives distinctive 

 characters to the main groups of 

 these Fungi. Thus in the Gastero- 

 mycetes the fructification is closed, the basidia being produced inter- 

 nally, and the spores set free by rupture, as in the Puff-Balls. In the 

 Hymenomycetes the basidia are borne collectively in a definite layer 



FIG. 387. 



Psalliota (Agaricus) campestris. Mush- 

 room. The hymenium covers the surface 

 of the radiating, downward-directed gills. 

 To the right a young fructification. 

 (Reduced.) (From Strasburger.) 



