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.
Fig. 173.—The cultivated Mushroom (Psalliota campestris).
The mycelium mostly grows in soils rich in humus or dung, on decaying trees and similar objects. Many species, e.g. Tricholoma personatum and Marasmius oreades, form the so-called “fairy rings.” The fruit-bodies in these species are confined to a larger or smaller surface on which they are very regularly arranged in a ring. The reason for this is found in the radial growth of the mycelium, so that the oldest portion, or the starting point, is found at the centre of the ring, and the younger ones, on which the fruit-bodies are formed, at the circumference. The older hyphæ gradually die, and at the same time, the radial growth continuing, the ring of fruit-bodies becomes larger and larger. The “fairy-rings” are marked not only by the fruit-bodies, but also by the more vigorous growth and darker colour of the grass upon these spots.
Some species are parasites. An example is presented by Armillaria mellea, a remarkable and very destructive Fungus in woods and forests (Figs. [176], [177]). In addition to the filamentous, white mycelium, it has also black, or black-brown, horny, root-like mycelium-strands (rhizomorpha) which were formerly considered to belong to a special genus of Fungi described under the name “Rhizomorpha.” The mycelium lives parasitically on the Conifers and other trees, forcing its hyphæ into the bark and between the bark and wood, and thence penetrating into the wood so that the tree is very severely attacked. It may also live saprophytically, and clusters of fruit-bodies are often found on old stumps and stems, on old timber, and in the rich soil of woods. The rhizomorpha, living underground, can extend for considerable distances and infect the roots of neighbouring trees, and spreads in this way the diseases known as “Harzsticken” and “Bark-Canker,” which are very destructive to young trees.
Fig. 174.—Psalliota campestris. A Tangential section of pileus showing lamellæ (l). B Portion of gill more highly magnified; t trama; hy hymenium with basidia and basidiospores; sh, subhymenial layer. C A portion of the same more highly magnified; s′ s′′ s′′′ s′′′′ various stages in the development of basidiospores; q paraphyses.
The chief characteristics by which the numerous genera are separated are the presence or the absence of the two kinds of veils, the nature of the fruit-body, the form, branching of the lamellæ, and their position and relation with respect to the stem, the shape of the pileus, the colour of the spores, etc., etc. A knowledge of the colour may be obtained by placing the pileus with the lamellæ turned downwards on a piece of white or coloured paper, so that the spores, as they fall off, are collected on the paper, and the arrangement of the lamellæ can then be clearly seen.
