298 FUNGUS-FLOEA. 



AGARICINEAE. 



The Hymenomycetous type of structure attains its 

 maximum of development in certain of the members of the 

 present group, characterised more especially by having the 

 hymenium spread over radiating gills or lamellae. 



In the most highly evolved forms the entire fungus when 

 young is enclosed in a primary or universal veil which is 

 ruptured during the elongation of the stem, the lower 

 portion remaining attached to, and sheathing the base of the 

 stem, and known as the volva. The volva may be more or 

 less free and readily separable, or entirely adnate or grown 

 to the substance of the stem. The upper portion that is 

 carried up on the piletis is torn into patches or warts as the 

 pileus expands. A secondary or partial veil is also present in 

 some species, spreading as a thin membrane from the upper 

 part of the stem to the margin of the pileus ; as the pileus 

 expands the veil breaks away from its margin and remains 

 on the stem as a frill-like ring. In some species both 

 universal and secondary veils are present, in others the 

 universal veil only, whereas in others the secondary veil 

 alone is present ; finally there are numerous species not 

 possessing a trace of either universal or secondary veil. 



In the great majority of species the stem is central, but in 

 some species it grows from the margin of the pileus, and is 

 said to be lateral; in others again it is entirely absent, when 

 the pileus is described as sessile, and is either attached by a 

 broad base and stands out horizontally, when it is dimidiate, 

 or is attached by the pileus to the wood or bark on which it 

 is growing, hence the gills are uppermost, and exposed to the 

 light, in which case it is described as resupinate. 



The most important feature in the discrimination of 

 genera turns on the mode of attachment of the gills to the 

 stem. When the gills are attached or grown to the stem, 

 and run down the latter for some distance, they are said to 

 be decurrent. The opposite extreme to the last-named 



