The Fungi are enormously numerous. No less than 2,000 of the highest and most conspicuous of these plants have been figured; many more have been described; multitudes of those inhabiting the torrid zone are unknown; and the microscopic and parasitic tribes are innumerable. Though with a few exceptions entirely formed of cellular tissue, the fungi resemble animals in respiration and chemical constitution. They contain more azote than any other of the Cryptogamia, and obtain it chiefly from their food, which consists of animal and vegetable substances alive, dead, or decomposed. They inhale oxygen, and exhale carbonic acid gas, so that they never form true chlorophyll. No plants are more dependent on heat and moisture; many perform all the functions of life and reproduction independently of light, preferring dark and shady places to sunshine.
The Fungi form two principal groups, distinguished by their mode of fructification. In the higher group, Sporiferi, the fungus produces naked spores either single or compound, by means of which it may be multiplied. In the lower group, Sporidiiferi, the fructification consists of sporidia, enclosed in a distinct sac. The Sporiferi include the following orders, Hymenomycetes, Gasteromycetes, Coniomycetes, and Hyphomycetes. The Sporidiiferi include the Ascomycetes and the Physomycetes. These various groups we may now proceed to examine.
The most important family of Fungi is, without question, that of the Hymenomycetes, the species of which far excel all others in their richness of colouring, and beauty of form. In this group the hymenium is free and mostly exposed. It comprises six orders, of which the Agaricini hold the first place. The genus Agaricus alone comprises 1,000 distinct species, which assume as many different forms and colours, with only slight modifications of substance, and it surpasses in number of species all the other generic groups known.
The Agaricus campestris, or common mushroom, is a type of that vast group; it consists of two distinct parts, the nutritive and reproductive. The nutritive part is the mycelium or mushroom spawn of gardeners, which resembles a mass of white spider’s threads mixed in inextricable confusion, and carries on for a time all the functions of the plant. Mycelia may exist for years without bearing the reproductive part, but fruit never can be produced without spawn. The mushroom itself, which springs from the spawn, is the fruit-bearing part, in which the spores are formed and ripened. It is distinguished by a kind of hat or bonnet called the pileus, supported by a stem. The pileus is lined by a number of gill-shaped plates or lamellæ radiating from a common centre; they are the reproductive organs in which the spores are produced by free cell formation, a process always preceded by a concentration of the matter within the parent cell, which is then divided into as many nuclei as there are to be spores. In the higher fungi, the number of spores thus formed is definite; in the Agarics they are in groups of four placed at the extremity of a stem, springing from the summits of these reproductive gills. Most of the Agarics rise from the ground without any cover; the pileus or cap may show every variety from a smooth polished surface to hairs or shaggy scales, but some of the more highly organized have a general wrapper or volva, which encloses the whole plant, and bursting at last, it leaves some traces behind. In others, the pileus is at first clothed with fibres, which vanish or leave traces on its margin forming a veil or curtain. Some have a membrane attached to the stem, either connected with the volva, or spread under the gills when young, and, when more or less persistent, it is called a ring.
The spawn, which is the earliest product of the spore, has a great variety of forms. Sometimes it is filamentous, sometimes tubular, creeping extensively, or concentrated in a felted mass, sparingly developed, or produced in abundance. Besides, it is developed in a great variety of situations often difficult to detect. The fructification is alone evident, under innumerable forms, which are as rapid in their growth as they are for the most part ephemeral in their duration. Some species have been known to acquire several square inches of surface in a single night; the plant, however, is often far advanced before it appears above ground. Some Agarics grow most readily after thunder storms and abundant rains; certain species are always single; others grow in dense aggregations; while in several species there is a tendency to assume a circular arrangement, and that not merely when the spawn is perennial, but when the whole existence of the fungus is confined to a few days or weeks.
A mass of spawn is not always produced by a single spore, but by a collection of spores, from whence it spreads in every direction, and forms a common belt. In the Agaricus arvensis, Marasmius Oreades, &c., it spreads in a circle and bears fruit; and, as it continues to spread, the same process takes place at each circumference. In this way are formed the Fairy Rings so frequently seen in pasture lands. The fairy rings are sometimes of very ancient date, and attain enormous dimensions, so as to be distinctly visible on the side of a hill from a considerable distance. It is believed that they originate from a single fungus, whose growth renders the soil immediately beneath unfit for its reproduction. The spawn, however, spreads all around, and in the second year produces a crop, whose spawn spreads outwards again, for the soil behind forbids its return in the opposite direction. Thus the circle is continually increased, and extends indefinitely till some foreign cause destroys it. The manure arising from the dead fungi of the former years makes the grass vigorous around, so as to render the circle visible even when there is no external appearance of the fungus; and the contrast is often the stronger from that immediately behind it being killed by the old spawn. This mode of growth is far more common than it is supposed to be.
The depth to which spawn penetrates and the rapidity of its growth even in the hardest timber if exposed to damp is quite astonishing. Instances occur in which the spawn of dry rot not only enters wood, but penetrates solid structures of brick. It overcomes an immense resistance.
The genera of the Agaricini differ in substance; some are almost ligneous, others leathery or tough, occasionally they are delicate and deliquescent, and although most of them are entirely formed of cellular tissue, the Lactarii and Russulæ form remarkable exceptions in having laticiferous vessels mixed with their cellular structure. These vessels exist in all parts of the plants, especially in the gills, where they give out the liquid on the slightest touch. In the Russulæ it is watery; but in the Lactarii, in which it is either mild or acrid, according to the species, it is also of different colours, which sometimes change their tint upon exposure to the air, probably from ozone. In all fungi there is a small amount of poisonous matter, and the quantity in any given species is extremely uncertain, so that the same fungus which may be eaten with safety in one country, is deleterious in another.
In the dark coal mines at Dresden, luminous Fungi cover the roof and pillars with the most dazzling phosphorescent light, which increases with the temperature of the mine. Agaricus Gardneri, a species parasitic on the Pintado palm in Brazil, is highly luminous; and the Agaricus olearius in the south of France also possesses that rare quality. The gills under the pileus shine as brightly as a glow-worm, in the dark crevices of the olive stems in November and December. M. Tulasne found that the light was extinguished in vacuo or non-respirable gases, whence he concludes that it is due to a slow combustion without heat, arising from a chemical combination of the oxygen of the atmosphere, inhaled by the fungus, with a substance peculiar to the plant.
In a few Agarics the cells are so connected by veins or lateral branches, that they assume the character of pores, as in the Chantarelle, a sweet-scented lemon-coloured fungus, whose gills pass into mere veins, and its inferior fruit-bearing surface is all but even and uniform, so that it forms a connection between the Agarics and the Polyporei, a most extensive order of the higher fungi, essentially distinguished by having a multitude of pores in the smooth under-surface of the pileus, instead of gills. The pores are generally small; in some species they are hexagonal, and so large that they look like a honeycomb. In all, they are the mouths of cellular tubes, packed closely together side by side, or more closely connected, sometimes easily separated, sometimes inseparable. They constitute the fructiferous surface or hymenium of the fungus, and contain the spores. This structure gives the pileus a thick heavy appearance, and a vast variety of characters; besides, the substance itself varies in density and colour. The stem also may be long or short, sometimes wanting altogether, when the pileus or cap is attached to the surface on which the fungus is growing. The growth of individual fungi, whether Polyporei or Agarics, is centrifugal, that is, they spread from the centre of the pileus, as in the Polyporus fraxineus, which involves every stick and blade of grass it meets with as it increases in diameter, and continues to increase for years, till it is occasionally a yard across.