FUNGI, an order of acotyledonous or cryptogamous plants, containing a very great number of species, nearly 5,000 being known, whilst it is probable that the whole number existing is very much greater. They are amongst the lowest forms of vegetable life, and some naturalists of no mean reputation have entertained the notion that they spring into existence in certain circumstances, not from germs previously existing, but from a mucus capable of organization, or through changes iu the cells of more highly organized plants, and of animals in states of disease or of decay; an opinion which, however, is more generally rejected as having no foundation in accurate observation, as not necessary to explain the readiness which certain F. almost invariably spring up in certain circum stances—from which is derived the chief argument in its favor, as opposed to all i analogy of ascertained facts, and as rendered improbable by the abundant provision which all the F. possess for the perpetuation and diffusion of the species. F. are cellular plants, the cells sometimes elongated so as to become filaments. They consist of a thallus, which spreads in a matrix, and is nourished by it, and from which stems are thrown up into the air, bearing the fructification. The organs connected with fructifi cation arc often the principal part of F. and the thallus very small, consisting of a few cottony threads, or ciosely compacted cells, or even altogether undiscernible. Not 'infre quently, however, the proportion of the thallus is comparatively great, and in circum stances unfavorable to the development of the organs of fructification, it extends itself greatly in the matrix, as in the case of dry rot, ergot, etc. (q.v.), and even of the common mushroom. The thallus of F. is called mycelium (Gr. makes, a mushroom), and in mushrooms and some other kinds is further popularly as the spawn. F. are nearly related to algae and to lichens, but differ from both in deriving their nourishment from the earth or from the bodies upon which they grow, not from the medium by which they are surrounded. They differ also from lichens in their generally much softer sub stance and their. fugacious character; also in being quite destitute of green granules (gonidia) in the thallus, which are characteristic of that order. They differ from alga: in not living immersed in water or other liquid, but producing their fructification in air. The lowest forms of F., and the lowest forms of alga?, are sometimes, however, not easily distinguished; and the mycelium of some F. is capable of spreading in a liquid, and assuming a modified appearance extremely resembling that of some alga?. It is supposed to be the presence of the myceliumn of certain F. which makes liquors " inothery;" and to a similar cause is ascribed the ropiness of the dough in some bakehouses, an evil not easily cured.—From other plants in general, F. differ in their chemical composition, which is remarkably nitrogenous, and assimilates them to animal organisms; whilst, unlike other plants, they do not absorb carbonic acid from the air, and give out oxygen, but, like animals, absorb oxygen, and give out carbonic acid; so that some naturalists have proposedIo constitute for them a distinct kingdom of nature intermediate between the animal and the vegetable.
F. are very various in size, many being scarcely visible without a microscope, whilst others are some feet in diameter. Even the same species, however, often exhibits great variety, not only in size, but in other p-rticulars, according to the differ ent circumstances of its growth, causing great difficulty to the botanist, whilst further difficulty arises from the modifications of imperfectly developed mycelium, of which many spurious genera have been constituted. A great resemblance in general appear ance to F. is sometimes exhibited by diseased portions of leaves, etc., and by the secre tions caused by the attacks of insects.—When the spore (seed) of a fungus germinates, it sends out radiating filaments, which generally branch and interlace, and portions of this mycelium removed to another favorable situation, grow there, so that F. are propa gated by this means as higher plants are propagated by their tubers or by the division of their roots. The F. of simplest structure or lowest organization consist of nothing more, when they have reached their fullest development, than masses of spheroidal cells, spores, breaking up into a fine powder, as in some of the small parasitic species which are very injurious to corn. Sometimes these cells are united into jointed threads. In species of rather higher organization, the plant consists of jointed threads, but the spores are formed in the enlarged terminal joints, and are dispersed by their bursting. In the higher kinds, the spores are produced in or on peculiar organs of extremely various shape and character. In some, as puff-halls, the whole interior of the plant is filled with the fructification. In agarics, boleti, morels, etc., the fructification takes place on a particular membrane, a part of the external surface of the plant called the hymenium, variously situated (in agarics on the under side of the pileus or cap), the extent of which is often greatly increased by wrinkles, plates or gills, pits, pores, etc. These form the highest division of F., called hymenomyeetes, in the system of Fries, the greatest continental authority in mycology, as this department of botany is sometimes termed. Berkeley, who, without any near rival, occupies the first place among the mycologists of Britain, divides F. into two "classes;" the first class not hav ing the spores inclosed in tubular sacs (asci) or vesicles. and containing the " orders" hymenomycetes (agarics, boleti, etc.), gasteromycetes (puff-balls, etc.), coniomycetes (rust, smut, etc.), hyphomyeetes (mold, mildew, botritie, oidium, etc.); the second class contain ing two orders, ascornyeetes (morels, truffles, etc.), in which the spores are definitely arranged in asci, and physomycetes (some kinds of mold, plants which gro'w on ferment ing substances, and some of the minute pests of cultivated plants), in which the spores are in vesicles without definite arrangement.