_The Pileus._—By far the larger number of funguses mentioned in this work have a pileus, or cap; all such belong to the first great tribe _Pileati_; they include the genera _Agaricus_, _Boletus_, _Cantharellus_, _Morchella_, _Hydnum_, _Fistulina_, and _Polyporus_, each of which furnishes its quota of alimentary species, together with many others not esculent. The form of the pileus, like that of the stalk, is various in these different genera, besides being variable in the different species of the same genus; generally it assumes an orbicular or umbrella shape, especially in such funguses as grow solitary on the ground, whilst in others, parasitical on trees, (particularly when they have no stalk,) it is more or less of a half-hemisphere. _The Gills._—Those vertical plates on the under surface of the mushroom, which radiate from the centre to the circumference, like the spokes of a wheel, are called Gills (_lamellæ_); they are not formed, as some have supposed, of layers of the reduplicated seed-membrane alone, but by a prolongation of the fibres of the pileus, which these merely invest. The fibrous structure is most apparent in Agarics with thick gills; in those where the flesh changes colour when bruised; or where, the interposed flesh remaining white, the hymenium is tinged with the colour of the ripening spores. In those funguses which have little flesh the upper surface of the pileus, especially towards the circumference, is frequently furrowed with transverse sulci; these are occasioned by the sinking in of the epidermis along with the fibres of the flesh between the layers of the hymenium, and consequently their position always corresponds precisely to that occupied by the backs of the gills. The end nearest the stalk is termed posterior (_postica_), the opposite extremity anterior (_antica_); the terminations of the lesser gills take place at various distances short of the stalk, which the perfect gills reach, and down which they sometimes course or are decurrent (_decurrentes_); they are said to be adnate (_adnatæ_) when connected at their posterior end; free (_liberæ_) when they do not adhere; remote (_remotæ_) when they terminate at a certain distance from the stem; emarginate (_emarginatæ_) when they are obtusely notched or hollowed out posteriorly; denticulate (_denticulatæ_) when connected by means of a tooth; equal (_æquales_) when all of the same length; forked (_furcatæ_) and branched (_ramosæ_) when they divide in their course, once, or more frequently, or are connected at the sides with the imperfect gills; dedalean (_dædaleæ_) when they anastomose irregularly together; simple (_simplices_) when they are free from all connections; distant (_distantes_) when they are few and wide apart; close (_confertæ_) when they are very numerous and touch each other; serrated (_serratæ_) when notched like a saw; waved (_undulatæ_) when the margin is undulating; and imbricating (_imbricatæ_) when they lie one over another, like tiles.