Plants more or less fleshy, upright (never spread over the surface of the substratum), simple or branched. Hymenium covering both sides and the upper surface. =Clavariaceæ.= 200 =4=--Basidia forked or longitudinally divided; or if continuous then globose, or bearing numerous spores; or if the plant is leathery, membranous, or floccose, then basidia as described. Hymenium covering the entire free surface or confined to one portion; smooth, gyrose, folded or lobed; or hymenium lamellate, porous, reticulate or toothed forms which are gelatinous and provided with continuous basidia may be sought here. =Tremellineæ.= 204 FAMILY AGARICACEAE. Pileus more or less expanded, convex, bell-shaped; stipe central or nearly so; or the point of attachment lateral, when the stipe may be short or the pileus sessile and shelving. Fruiting surface usually on the under side and exposed toward the earth, lamellate, or prominently folded or veined. Lamellæ or gills radiating from the point of attachment of the pileus with the stipe or with the substratum in the sessile forms; lamellæ simple or branched, rarely anastomosing behind, clothed externally on both surfaces with the basidia, each of which bears four spores (rarely two), cystidia often present. Key to the North American genera. THE WHITE-SPORED AGARICS. (Sometimes there is a faint tinge of pink or lilac when the spores are in bulk, but the color is not seen under the microscope.) =Plants= soft, fleshy or nearly so, usually soon decaying; dried plants do not revive well when moistened. 1 =Plants= tough, either fleshy or gelatinous, membranaceous, corky or woody, persistent, reviving when moistened. 13 =1=--=Gills= acute on the edge. 2 =Edge= of the gills obtuse, or gills fold-like, or vein-like, but prominent. 12 =2=--=Trama= of the pileus of interwoven threads, not vesiculose. 3 =Trama= of the pileus vesiculose, plants rigid but quite fragile. 11 =3=--=Gills= thin, not much broadened toward the pileus. 4 =Gills= broadened toward the pileus, of waxy consistency. =Hygrophorus.= 110 =4=--=Stipe= central or sub-central. (Some species of Pleurotus are sub-central, but the gills are usually not decurrent.) 5 =Stipe= on one side of the pileus, or none, rarely with the stipe sub-central. (Some species of Clitocybe are sub-central.) =Pleurotus.= 102 =5=--=Stipe= fleshy, pileus easily separating from the stipe, gills usually free. 6