The fructification of the Fungi occurs in two distinct forms, in one of which the seeds or spores are naked, and situated at the ends of slender cells or filaments, whilst in the other the spores are contained in usually flask-like cells, called asci, similar to those occurring in the Lichens. In a few Fungi, antheridial organs, called spermogonia, as in the case of the Lichens, have also been detected. The Fungi are divided into six Orders, from each of which a few species may be selected to illustrate their structure more in detail.
Hymenomyce´tes (ὑμἠν, membrane, μὑκης, fungus). This is the highest Order of Fungi, containing a large number of genera and species; as examples of which may be mentioned the common Mushroom, Toadstools, &c.
Their general structure may be illustrated by the examination of the common Mushroom (Agar´icus campes´tris); the species figured ([Pl. VII.] fig. 1), however, being Agaricus micáceus, which is common at the root of trees, the bottom of decaying posts, &c.
The vegetative part of the fungus consists of a cotton-like mycelium, which is composed of slender, colourless, interwoven filaments, popularly known as the spawn. The portion commonly called the mushroom corresponds to the fructification, and consists of certain parts visible to the naked eye. These are an expanded portion at the top, forming a hemispherical cap, receptacle, or píleus (pileus, a cap), and a stalk, or stípes, upon which the cap is supported. On the under surface of the cap are a number of nearly parallel, radiating, dark-coloured plates or gills, somewhat resembling the gill-plates of a fish. The dark colour of the gills arises from the presence of the spores, which are coloured, although in some species they are white. The surface of the gills, upon which the spores are situated, is called the hyménium (ὑμἠν, membrane). The spores ([Pl. VII.] fig. 2 a) are microscopic and very minute, and are situated at the ends of little stalks or points ([Pl. VII.] fig. 2 b), called sterig´mata (στἡρυγμα, a prop), which are four in number, and consist of prolongations of the colourless cells of the hymenium; and these cells are the basid´ia (βασἱδιον, a little base). The detection of the basidia requires great care, as they are very minute and transparent; the best way to observe them is to cut a very small portion from the uninjured edge of one of the gills with a fine pair of scissors, and to examine it in water. If the gills have been bruised, the spores are easily rubbed off, and their connexion with the basidia destroyed.
In the young state of the Mushroom, the fructification appears as little knobs upon the spawn or mycelium. Upon cutting these through perpendicularly, the cap and stalk are found to be enclosed in a skin or wrapper, called the vol´va (volva, a wrapper), and the margin of the cap is continuous with the surface of the stalk, the connecting membrane forming the veil, or vélum (velum, a veil). As the Fungus grows, the cap rises and bursts the volva, which withers and disappears; and the veil is torn through, the portion remaining in connexion with the stalk encircling it as a collar or ring (an´nulus).
Merúlius lach´rymans, the Dry-rot Fungus, which belongs to the same family (Agaricíni) as the Mushroom, deserves notice from its very destructive action upon decaying timber. The filaments of the mycelium may readily be detected in the rotting wood by examining a thin section in water. The receptacle forms a yellowish-orange or brownish flattened mass, some inches in breadth, with white downy margins; and the surface exhibits folds arranged so as to form large irregular pores, instead of gills as in the Mushroom.
In other families the cap and stalk appear fused together and undistinguishable; or the fructification assumes the form of the cap or the stalk only, and the hymenium does not form gills. Thus in the family Polyporei (the members of which are common on the trunks of trees and on rotten posts, and some of which are very large) the basidia are situated upon the inner surface of tubes immersed in the under part of the mass, their orifices forming minute pores, yet visible to the naked eye. In other families the basidia are placed upon the outer surface of a club-shaped or branched receptacle (Clavarini), or upon external prickle-like points (Hydnei), &c.
In the family Tremellini the receptacle forms a gelatinous mass, and the basidia are situated upon its surface, terminating the filaments of which it is composed. One species, Dacrymy´ces stillátus, is very common on fir posts in the winter and spring, forming little roundish, yellowish-orange, cushion-like masses.