128 INTRODUCTION TO THE STUDY OF FUNGI 



may be traces of the fissure on the basal portion. In the 

 most highly developed forms patches of the broken envelope, 

 or volva, adhere like warts to the top of the pileus, whilst the 

 basal portion remains as a loose sheath at the bottom of the 

 stem, where it is for some time persistent as a kind of sheath, 

 called the mlva. By cutting through the entire Fungus longi- 

 tudinally from the apex to the base, the cut section exhibits 

 the following features — a rooting mycelium, or spawn ; an erect 

 stem rising therefrom (.s), winch is sometimes solid and some- 

 times hollow (Fig. 49) ; the base either equal in dimensions or 

 swollen like a bulb, occasionally with a distinct outer coat or 

 volva {v), which is adnate below to the bulb and free above ; the 

 stem is surmounted by a more or less hemispherical or conical 

 cap or pileus (/?), the under surface covered with parallel plates, 

 or gills, which radiate from the stem to the margin of the cap 

 {g). When the cap is hemispherical the gills are often covered 

 at first by a thin membrane, which extends from the stem to 

 the edge of the cap ; and, as growth and expansion proceed, this 

 veil is torn away from the margin of the pileus, and hangs like 

 a collar or frill around the upper part of the stem, forming an 

 anuulus or ring (a). When the cap is conical the edges of the 

 gills are closely applied to the stem vertically, and the edge of 

 the cap is only slightly attached to the stem, not forming a 

 ring. When the substance of the cap descends between the 

 folds of the gills it is the trama, and then the gills do not 

 part freely from the cap ; but when the trama is thin or 

 obsolete, the gills part freely from the flesh of the pileus. The 

 gills are formed by a membrane, which constitutes the hymen- 

 ium, and is folded like a fim ; so that each gill is a double 

 membrane, applied back to back, giving as much surface as is 

 possible for the production of the spores. The appendages of 

 the hymenium have already been described as basidia, cystidia, 

 and paraphyses, with the resulting tetraspores. Thus much 

 may be seen of the structure in a longitudinal section of the 

 pileus and stem. Modifications in some one or more of these 

 general details give rise to the different genera into which the 

 Agaricini are now divided. In former times, when the system 

 adopted by Fries absolutely prevailed, the greater part of the 

 species of Agaricini were comprised in one large genus, that of 



