8 G, MASSEE OX BASIDIOMYCETES. 



included under the name of " toadstool," the gills are situated 

 on the under side of the cap or pileus, radiating from a central 

 point round the stem, a given number of the gills extending from 

 the stem to the margin of the pileus, shorter gills occupying the 

 gaps between the primary ones as the margin of the pileus is 

 approached. By this arrangement of closely packed gills, an 

 enormous area of hymenium or spore-bearing surface is furnished 

 at a very small cost of material — certainly very much more than 

 in any of the preceding families. The simplest types of agarics, 

 as illustrated by species of Pleurotus, Marasmius, and Can- 

 tharellus, are very minute, often not more than one to two lines 

 across, stemless, with very few, narrow, and widely separated 

 gills, and furthermore, are entirely destitute of protection against 

 climatic influences, the fungus being attached by the pileus, and 

 the gills consequently pointing upwards, without an}^ special 

 covering from the first. Next we meet with forms growing out 

 horizontally from trunks, posts, etc., either stemless or with a 

 short stem springing from the margin of the pileus, and the gills 

 radiating from the point of attachment of the stem in a fan-like 

 manner ; in these forms the gills are on the under surface of 

 the pileus. Finally we reach the highest known type of 

 structure, as presented by the common mushroom {Agaricus 

 campestris, L.), where w^e find the cap supported on a central 

 stem and bearing the gills on its under surface. In many of 

 the mushroom type of structure, the gills are protected during 

 the young stage by a membrane stretching from the stem to the 

 margin of the pileus, as described under Polyporus. Finally 

 many of the most perfect forms are enclosed in a thick, felt -like 

 sheath or volva, which conceals the entire fungus during the 

 period of formation of the various organs, pileus, gills, stem, etc., 

 which takes place underground. When everything is ready 

 the stem elongates rapidly, raising the fungus above ground 

 for the purpose of enabling it to eftect the distribution of its 

 spores. As the fungus appears above ground, the volva or 

 sheath, having effected its object, is ruptured, a portion being 

 carried up on the cap, where it persists under the form of 

 irregular patches or warts, so conspicuous on the scarlet pileus 

 of the fly agaric [Amanita onuscaria), and many other species. 

 Protection against living enemies is very evident in members of 

 the present family, under the form of alkaloids, toxalbumens, 



