Order 6. =Agaricaceæ= (=Mushrooms=, =Toadstools=). _The hymenophore consists_ of knife-like plates (_lamellæ_, _gills_), which are situated on the under side of the umbrella-like pileus of the fruit-body, and radiate from the central stalk. Those which are first formed extend from the edge of the pileus to the stalk; those formed later reach only a longer or shorter portion of this distance, according to their age. In structure the lamellæ (Fig. 174) consist of a central mass of hyphæ, the _trama_, continuous with the hyphæ of the pileus; these terminate in a layer of shorter cells, the _subhymenial layer_, immediately beneath the hymenium which is composed of basidia and paraphyses. In a few species, but not in the majority, the lamellæ are branched, and in some they are decurrent. A few have the stalk placed excentrically, or it may be entirely absent. [Illustration: FIG. 172.--Development of _Psalliota campestris_: _a_, _b_, _c_, _d_ show the various stages of the development of the fruit-bodies and the mycelium (_m_) (nat. size); _e_ the fruit-body in a somewhat later stage, slightly magnified; _f_ longitudinal section of _e_; _n_ first formation of the hymenium; _g_ longitudinal section of a more advanced fruit-body (nat. size); _n_ the hymenium; _o_ velum partiale (see Fig. 133.)] In the early stages of its development the fruit-body is more or less enclosed in a hyphal tissue--the “veil” (_velum universale_, or _volva_). The veil at first completely encloses the young fruit-body, but is afterwards ruptured as the latter grows, part remaining at the base of the stalk as the “sheath” (_annulus inferus_), and part on the pileus as scales or warts. In the “Fly Mushroom” (_Amanita muscaria_) the remains of the veil are especially conspicuous as white patches on the bright red ground of the upper surface of the pileus, and as a sheath at the base of the stalk (Fig. 178 _v._). Another veil--the _velum partiale_--a hyphal tissue (Figs. 178 _a_; 173) stretches from the edge of the pileus to the stalk, and encloses the lamellæ. This veil is ruptured as the pileus expands, a portion attached to the stalk remaining as the “upper ring” (_annulus superus_) (Figs. 173, 178 _a_), or a part attached to the pileus hanging down as a fringe round its edge.--Some genera have no veil, the under side of the pileus being exposed from the first (_gymnocarpic_ Agaricaceæ). Those which have a veil (_hemiangiocarpic_ A.) afford a transition to the angiocarpic Gasteromycetes. [Illustration: FIG. 173.--The cultivated Mushroom (_Psalliota campestris_).]