Fungi (Gr. a sponge), an extensive family of cryptogamic plants, generally known under the names of mushrooms, toadstools, rusts, smuts, bunt, and mildews. With rare exceptions, they are parasitic plants, growing upon and drawing their nourishment (or at least a part of it) from the substance of the object they infest. Fungi occur in all parts of the globe, finding their maximum in the moist temperate zones; abounding in a climate like that of Sweden, which has produced more species upon a given area than any other known locality, except perhaps the southern United States. They are found wherever there is decaying vegetation, upon which they feed; they often prey upon living tissues, which they destroy by their attacks; their vegetating fibres are of such extreme minuteness that they penetrate the hardest woods, and powerfully hasten their decay. Nothing of vegetable origin is free from their ravages when exposed to influences favorable to their growth. They are found also on animal dejections, on insects, whose death they cause, on the human skin, and even on bare stones, on iron which was in a forge a few hours before, on lead, and on chemical solutions.

The disease in silkworms is caused by a mould (botrytis bassiana). The flies found adhering to windows in autumn, fixed by the proboscis, are destroyed by a mould (sporendo-nema muscoe), which produces the little white rings between the abdominal segments and discharges its seed upon the glass around like a little cloud. The celebrated caterpillar fungus of New Zealand (cordyceps Robertsii), which infests the caterpillar of hepialus virescens, is a remarkable instance. American caterpillars are destroyed by other species. The larva of the common May beetle (lachnosterna quer-cina), which passes three years of its destructive life under ground, is sometimes attacked by a fungus which soon causes its death. Ony-gena equina grows on the hoofs and horns of animals. Some of the microscopic species cause cutaneous disorders in the human system, and others have been found in the brains of birds. (See Epiphytes.) - Notwithstanding the long time which has been given to the study of fungi, there is no class of organized structures so little known. Their microscopic character, their abnormal growths, their polymorphic forms, have baffled the researches of the closest observers.

It is only within a comparatively short time that an approach has been made to a clear insight into their laws of growth and reproduction. Some even now deem them to be of spontaneous or chemical origin, an opinion which their sudden appearance in vast numbers after a long rest, and their occurrence in closed cavities, have tended to establish. But this idea has been clearly disproved. That they are perfect plants, growing from and reproducing bodies analogous to seeds, is too firmly established to be questioned. When we learn that a single plant produces millions of these reproductive bodies, so small that they float on the air scarcely influenced by the force of gravity, that they may remain an indefinite period inert, and be called into sudden vitality by atmospheric changes favorable to their germination, their sudden appearance can be readily understood. They have been traced through their metamorphoses. The infinitesi-mally small spore has been watched in its growth into a perfect plant; and one such observation, unquestionably made, is positive proof of their being perfect plants, having a development following certain laws.-Fungi are of purely cellular growth.

They form no woody fibre like flowering plants, though many become corky, woody, and horny in the course of their growth, nor do they form chlorophyl in their tissues. They consist of mere aggregations of homogeneous cells, but exhibit a wonderful variety of external forms. Their earliest vegetation is a prolongation of the membranes of their spores, a name given to their reproductive seminal dust, which, though performing the office of seeds, differs from true seeds in being mere individual cells. From these arises a delicate, minute, webby growth, called the mycelium, which is the true vegetation of the plant, and which gives rise to the reproductive bodies at once, or builds up a receptacle which contains them. It is this mycelium which penetrates and destroys the object on which it is parasitic. It is made up of radiating and intertwining fibres formed of rows of cells placed end to end. These are in many instances so minute that they easily traverse the tissues of living plants and the pores of solid wood. From this mycelium grow the spores, which in their simplest form consist of the terminal cell or cells, which drop off to form new plants. They are of the extremest minuteness, appearing to the eye like a mere cloud of impalpable powder.

As we rise in the scale, special branches and processes are formed to bear the spores, either singly or in groups. Still more complex forms build up a special organ called the peridium, within which the spores arise contained in little sacs termed asci. The large fleshy growths met with in the woods or on trees are processes belonging properly to the reproduction and not the vegetation of the plant. They are very disproportionately large compared with the mycelium, and consist of a main stem called a stipe and an expanded top called a pileus, on which these spores are borne in various ways, on gills, ribs, prickles, etc. The mycelium is sometimes reduced to a mere trace of evanescent, floccose growth; while the reproductive body becomes a fleshy mass, several pounds in weight. But the spores are always minute, being sometimes only 1/20,000 of an inch in diameter.-Fungi occupy an intermediate position between algae and lichens, into which orders they gradually merge at different points. Indeed, so nice is the distinction at times, that some systematists have reduced lichens to a suborder of fungi.