The vegetative body or thallus of fungi consists of filiform, cellular elements called hyphae. In one group, the Phycomycetes, the hypha usually consists of a single densely branching cell; but in most cases it is composed of a series of cells placed end on end. These hyphae ramify laterally much more frequently than dichotomously, and the usual mode of growth is by an apical cell which divides transversely; but in the bodies of the larger fungi intercalary growth also occurs (as in Rhizomorpha subterranea). A single hypha forms the complete thallus of the simpler fungi called Hyphomycetes, llaplomycetes, <fcc., but the bodies of the larger (compound) fungi are composed of a colony of hyphae, usually densely interwoven, more rarely running in parallel lines, but always more or less firmly adhering together. In many fungi (as in the stalk of the Phalloideai,fifixρι pileus of Russula, and Lactarius, in 8clerotia, and in the peridia of the Lycoperdaceae) the fully developed tissue consists of polyhedral cells, closely packed, and bearing resemblance to parenchyma. This texture, however, consists of ordinary hyphae, which, through pressure from adjacent parts, have been forced to assume this form. It bears the name of pseudo-parenchyma.

The Myxomycètes are the only large group of organisms usually classed with fungi which cannot be described as consisting of hyphae. These differ in so many ways and so widely from any fungal or indeed vegetable structures that a separate consideration of their position is necessary (see Order V.). Other exceptions of a minor nature have been made of such organisms as IIormisdum, Cryptococcus, &c., but it is now the general belief that these are merely reproductive bodies of more perfect fungi. The cells of fungal hyphae are of many shapes, but tho usual one is long and cylindrical, and the other shapes are more or less modifications"of this. The structure and growth of the fungal cell agree in general with those of the vegetable cell as it occurs elsewhere. At tho same time no group in the vegetable kingdom exhibits so many minor divergent histological characters—a condition which serves to mark its boundaries as a class of vegetables with great distinctness.

The Cell-Membrane.— In the numerous fungi which develop rapidly and have a short existence in the adult state, tho cell-wall is thin, tender, and structureless; but when a plant of this kind is accidentally checked in its expansion, tho result is the production of thick, homogeneous, unstratified membranes. On tho other hand, the cell-wall of tho more persistent species early acquires considerable thickness, which, in the adult state, often so increases that the cell has the appearance of a solid cylinder. These thick membranes vary from a woody to a gelatinous consistency, and are composed sometimes of more than one layer. In the Polyporei, Thelephora, Bovist a, Geäster, Tulostoma, <fcc., the cell-walls often exhibit (either after simplo immersion in water or on the application of chemical reagents) at least two layers, the outer firmer and often coloured, the inner softer and clearer. The cohesion of the filaments in these larger plants is brought about by their θeing densely interwoven, and also by the firm union and to a certain extent the amalgamation of the outer layers of the membranes. Spiral and ring-shaped thickenings are to be found in the capillitium cells of Batarrea and Podaxon carcinomatis, and pits are of constant occurrence in corresponding cells of the Lycoperdaceae, and in the filaments which bear the fructification of Dactylium.

Chemical analyses of the cell-membrane show that it possesses the elementary constituents of cellulose; but since the uncoloured and unthickened membrane does not commonly exhibit the characteristic reaction of cellulose towards iodine (neither simply nor after treatment with potash or Schultz’s mixture), nor towards many of the reagents commonly employed in testing typical cellulose, it is necessary to apply to it the special term fungal cellulose. In several special cases, however, typical cellulose is known to exist. The membranes of old cells frequently undergo a kind of lignification, and in this condition offer extraordinary resistance to such treatment as that with concentrated sulphuric acid.

The Cell-Contents.— The protoplasm of fungal cells has no special quality of importance to distinguish it from that of other vegetable cells. Professor Sachs states (Bot. Ztg., 1855) that under his observation the apices of growing hyphae seemed to consist of one mass, in which the membrane could not be distinguished from the protoplasm; but Professor De Bary (Morp. u. Physiol, der Pilze, <fcc.), on the other hand, finds that the same conditions as exist in similar situations in other plants obtain here, viz., a dense mass of protoplasm enclosed by a tender membrane—an experience endorsed by most mycologists. The existence of a nucleus was long denied, and. indeed its presence in the cells of the thallus has not yet been proved; but in the reproductive organs, where it had long been overlooked, its occurrence is not uncommon. Attempts to prove its existence in the cells of the thallus have not been wanting, but as yet with apparently no success: Schacht’s observations on this head are notably untrustworthy, since there is no doubt that he confounded the true nucleus in other fungal cells with drops of oil and such bodies. The formation of vacuoles takes place as in other vegetable cells. Oleaginous matter is present, often abundantly, in nearly all fungi, in the form of drops of various sizes. Water (cell-sap) is necessarily present, though the quantity varies considerably without serious injury to the plant. A good proof of this variation is to be found in the expansion or contraction of the filaments of many Hyphomycetes according to the supply of water. In fungi with firmer cell-membranes, air-bubbles take the place of the water which has evaporated, and the contraction of the hyphae is very inconsiderable.

The fungal cell is wholly destitute of chlorophyll, and, it may be safely stated, of starch also. Schlossberger and Döpping record their detection of starch granules in the extracted sap of Cantharellus cibarius ; but from their method of investigation it is highly probable that these were accidentally present.

The pigments of various colours to be found in many fungi are perhaps in most cases properties of the cellmembrane. Another class of them is peculiar to the cellcontents, and a third seems to pervade bath membrane and contents. Those peculiar to the contents are mostly of an oleaginous or resinous nature, and their occurrence is in the form either of minute particles distributed throughout the protoplasm, or of larger drops or granules scattered irregularly among the contents. From the pigments peculiar to the fungal cell there are to be distinguished those absorbed in an unaltered state from the substratum. An instance of this is to be found in Peziza aeruginosa, which owes its colour to the abnormally greenish wood on which it grows. It was long thought that the Peziza was the cause of the green colour, but a sufficient proof is contained in the facts that the wood is more frequently found green without any trace of the fungus than with it, and that the upper part of the fungus is sometimes uncoloured when the lower portion has become green. Moulds, and other fungi usually colourless, are occasionally stained with the colour of an unusual substratum. The subject of the pigments of fungi is one of which our knowledge is very incomplete.

Crystals of calcium oxalate are to be met with on the surfaces and in the intercellular spaces of many of the larger fungi; but in only two cases have they been found in the interior of the cell (Phallus caninus and Russula adusta). Cell-division takes place in the same way as in other plants.

The mycelium is the part of the thallus devoted to the functions of absorbing and storing nutriment. It consists of hyphae developed directly from the germinating filaments, but often on further growth intricately bound up (frequently anastomosing) with each other, usually in amorphous masses, but sometimes in more or less definite bodies. In the larger fungi a number of hyphae (in which case they run parallel to each other) are sometimes associated into bundles, like rootlets. The mycelium not unfrequently persists for several years. Mycelia in general bear so strong a resemblance to each other that it is usually impossible to determine the species to which they belong on their own characters.

A number of parasitic fungi possess peculiar organs called haustoria, which perform the function of extracting nourishment, and when necessary retaining the plant in its position. These are lateral branches of the mycelial hyphae of various shapes and sizes. In Erysiphe, the mycelium of which creeps over the surface of its host plant, the haustoria are emitted abundantly from the side of the hyphae next the epidermis, into which they penetrate and cause decay. They are in this case small and irregular in shape. On the Peronosporeae, the mycelium of which inhabits usually the intercellular spaces of living plants, haustoria are frequently present. In some cases, as in Cystopus candidus, they have the form of minute stalked globules, but in most other Peronosporeae they are irregular filamental protuberances, frequently branching to such an extent as almost to fill the affected cell.

Sclerotia are tuberous bodies composed of densely interwoven mycelial hyphae enclosed by a layer of pseudo-parenchyma. They are specific in occurrence, like the bulbs and tubers of phanerogams, and are situated on or beneath the surface of the substrata—the ground or parts of plants. They were long regarded as independent forms of fungi, but it has been discovered that they are only resting states in which nourishment is stored up. They vary much in size.

The Receptacle.— On the mycelium there arises a body called the receptacle, the function of which is to bear the reproductive bodies, the spores. It varies much in size in different fungi; in most cases it forms the greater part of the whole thallus, and in others it consists of a simple or branched hypha. The same species of fungus may possess more than one kind of receptacle, either in different generations, or arising subsequently from the same mycelium. According to their structure receptacles may be divided into two groups, viz., those which consist of one hypha, and those which, composed of aggregated hyphae, form a compound body. In certain cases the receptacle is entirely suppressed (as in the interstitial oogonia of the Peronosporeae). When the receptacle consists of a simple or branched hypha, the spores are borne terminally. The sporophorous hyphae are branches of the mycelium, rising usually vertically from it, and themselves frequently so characteristically branched as to afford means of generic and specific distinction. After bearing the first spore, the sporophore may again grow for a short space before bearing another. In compound receptacles the fructiferous hyphae form together expansions called hymenia, from which the individual fertile branches arise. If the hymenium is formed upon the exterior surface of the receptacle it is termed gymnocarpous, and if within the receptacle angiocarpous. The hymenium never produces any but asexual spores.

Reproduction.— The reproduction of fungi is effected by both sexual and asexual means—the latter being far the more frequent of the two. No one species is known to possess more than one form of sexual reproduction, though it is frequently the case that more than one kind of asexual reproduction belongs to it. In many fungi no sexual reproduction is known to exist, but it is generally believed that in such cases the plants are merely members of a cycle of generations, the other stages in their life-history being unknown or unrecognized. The term spore is applied to all reproductive bodies, whether asexual or the product of the union of sexual cells. Discussion has frequently been engaged in as to the propriety of employing the same term to denote both kinds of bodies; but though in isolated c ιses the use of new terms has been advised, no satisfactory system of nomenclature has been established. There is, however, no doubt that some distinction ought to be made.

Sexual reproduction is effected by the union of two cells of different nature, which in themselves are incapable of further development. In the usual forms these cells are apparently of different nature, but in the phenomenon of conjugation the difference in the sexual elements is not determinable, though doubtless existing within the molecular sphere. The product of the union of sexual cells is developed into an organ of reproduction which, at the proper tim?, fulfils its office by giving rise either to a new mycelium directly or to a receptacle. These organs of reproduction bear names more or less expressive of their nature, such as zygospore, oospore, <fcc.

In those fungi of which the life-cycle is known, several different kinds of asexually produced spores have been observed. In only one group, the Phycomycetes, are motile spores (zoospores) known. In all other cases they arc produced either at the apex of a basidium (basidiospores) or similar sporophore (conidia, &c.), by cell-division, or within an ascus by free cell-formation (ascospores). In compound or septate spores, which are multicellular, each separate secondary cell is termed a merispore. Gemmae are produced by the breaking up (by cell-division) of hyphae into series of cells capable of germinating. The germination of spores is dependent chiefly on moisture, but to their farther development specific conditions are necessary, a description of which is beyond the scope of this article. The dissemination of spores is effected chiefly by the agency of the atmosphere and of water, and it is probable that insects or other animals have very little to do with it.

In their mode of life fungi are controlled by the absence of chlorophyll. Without it they cannot assimilate, and are therefore driven to obtain their nourishment by taking up the carbon compounds assimilated by other organisms. Their modes of life are either parasitic or saprophytic. As parasites they inhabit the bodies of living plants and animals, and even of other fungi. In some cases they kill their hosts, and in others encourage growth, as in the case of the Lichenes ', and between those two extremes various degrees of parasitism occur. As saprophytes they promote the decomposition of dead organic bodies, and thus aid in the production of carbonic acid, water, and ammonia, the elements of which return to the course of organic life. Jodin states that some fungi absorb as much as 6 per cent, of their nitrogenous contents in the form of nitrogen gas from the atmosphere. In the decomposition of fungi ammonia is formed from the nitrogenous compounds. As parasites and saprophytes their influence as regulators iu the economy of nature may be compared with that of the lower animals living the same mode of life.

Though the ravages of parasitic fungi are mostly confined to the vegetable kingdom, it is well known that many animals suffer from their attack. The occurrence of parasitic fungi on insects and fish is common; more rarely do they attack the higher animals or man. It has been strongly contended that the minute fungi play very important parts in many diseases of man, but this has usually been much exaggerated. The occurrence of Bacteria on the mucous surfaces of living bodies and on wounds has given rise to much discussion; and there is no doubt that insufficient knowledge of these organisms has often led to error, the observers not unfrequently mistaking the products of the decomposition of organic bodies, crystalline precipitations, &c., for Bacteria. It may safely be maintained that these are offener the concomitants than the causes of disease in man. A considerable number of fungi have also been described as playing active parts in various skin-diseases, but very little trustworthy information about their life-history has ever been gained.

The economic properties of fungi are of an unimportant character. A great number are poisonous, and many are edible; a few are used for medicinal purposes. Many of those described as edible, though they can be eaten without any serious consequence, are certainly not likely to become articles of food. At the same time it may be mentioned that much valuable food is annually lost through ignorance of the excellent esculent qualities of a few common fungi.

The phosphorescence or luminosity observed in several fungi has given rise to many absurd conjectures. This phenomenon depends on the respiration of oxygen, those fungi which exhibit luminosity ceasing to do so when the oxygen is extracted.

Geographical Distribution.— From the extreme poverty of our knowledge of the geographical distribution of fungi no general estimate can be even outlined. Of the fungi of by far the greater portion of the world we have no account, or at the best the meagre collections of passing explorers. Of even the European mycologie flora our knowledge is far from complete, Russia, Turkey, Spain, Portugal, and even Ireland, being only partially examined. Of countries in which the surveys have been more complete, only England, Scotland, Wales, Germany, France, and large districts of Austria, Italy, and Switzerland can be pointed to. Of the whole American continent the Carolinas alone are tolerably well known, and though collections have been made in Mexico, Texas, the island of Cuba, and a few tracts of South America, the examination of these countries has not been thorough. China, Japan, Siberia, and Further India are totally unexplored; but, on the other hand, Ceylon and the northern part of India are perhaps as well known as any other extra-European district save Carolina. From the Himalayas and northern India there are the collection and notes of Sir Joseph Hooker. In Africa, Algeria and the Cape have been examined, but from the tropical parts of that continent we have only the collection and notes of Dr Welwitsch, which are, however, of great value so far as the district he explored extends.

Any attempted scheme of geographical distribution would, therefore, be not only incomplete but open to great error, from the very partial accounts from the most of those districts which have been examined. As in other vegetables, heat and moisture necessarily exert the greatest influence on growth, and therefore on distribution. The character of the trees composing the forests of different countries, and the amount of cultivated land, subordinately affect the nature, if not the numbers, of the fungi inhabiting them. One broad principle, however, seems apparent, viz., that the large fleshy fungi, like the Agaricini, affect temperate countries more than tropical, and that those of a woody texture, like the Polyporei, inhabit tropical in preference to temperate countries. In the Arctic regions fungi are represented almost solely by the Lichenes. Of the distribution of microscopic fungi nothing of any value is known.

Classification.— Fungi are divided into orders and suborders as follows :— [table]

The above classification is broadly the same as that proposed by Professor De Bary. The principal characters of these orders and suborders are described below.

Order I.— Phycomycetes. —The Phycomycetes possess both sexual and asexual organs of reproduction. The sexually produced reproductive body gives rise to a generation bearing first asexual and then sexual organs, and the asexually produced reproductive body gives rise to a similar generation. The mycelium in this order consists of long densely-ramifying tubes or hyphae, on which the reproductive organs are borne.

Suborder I.—Saprolegnieae.— In this order the male organs are called antheridia and the female organs oogonia. In the monoecious forms these arise beside each other on the same plant. The oogonia are usually to be found at the end of short branches of the mycelium—very rarely sessile or intercalary. They are globular cells with one enclosing membrane containing dense protoplasm. In some cases (as in Saprolegnia monoica) the cell-wall soon becomes resorbed at various places, and the protoplasm divides into several globular bodies, which float in a watery fluid, the whole enclosed by the wall of the oogonium. In Aphanomyces, Pythium, and several species of Saprolegnia, only one globe is formed in the oogonium. The fluid in which these globes float is part of the watery contents of the globes expelled when the contraction took place. While these alterations are proceeding in the oogonia, the antheridia grow out from the same or some adjoining branch of the mycelium. These are thin, crooked hyphae, which frequently entwine the stalks of the oogonia in their growth; the tips of the tubes, however, on reaching the wall of the oogonium adhere, and the upper part...