FUNGUS (Gr. pvκηs, whence are derived mycetes, employed as a termination to the names of certain orders of fungi, and also the term mycetology, or more commonly mycology, the science of fungi) is the name applied to a distinct class of cellular cryptogams or Thcdlophyta. Though as plants the class is well marked by the invariable absence of chlorophyll, and consequently of the physiological phenomena attending its presence and action, it is not so at some points, where a dubious border exists between it and the lower members of the animal kingdom.
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 becomes separated from the rest by a septum. This process is usually contemporary with the contraction or separation into globules of the contents of the oogonia. The antheridia then push through the walls one or more tubes, which discharge from the points minute motile spermatozoids (about - g -¾ 75 - millim. in size), and these fertilize the globules. The globules then assume a cellulose membrane and are called oospores.
The oogonia are formed in the dioecious as in the monoecious species, but the antheridia in a totally different way. They arise within bladder-like protuberances of the mycelium, which are divided by transverse septa into a series of cells, each of which is an antheridium. In Saprolegnia dioica, the antheridium breaks up into numerous spermatozoïde; but in Adilya dioica a preliminary division of the antheridium into several portions precedes the formation of the spermatozoids. When free these spermatozoids move actively by means of one long cilium. Fertilization, and the consequent formation of oospores, are effected in a similar way to that described as occurring in the monoecious forms. . Doubt has been expressed as to the described monoecious fertilization, but on the whole it may be regarded as generally true. The oospores of the Saprolegnieae are double-coated. After a long period of rest they emit germ-tubes, but it has been recorded that they sometimes produce zoospores, when the resting state is shorter.
The zoosporangia or asexually-produced organs of reproduction are terminal cells (very rarely intercalary), sometimes irregularly cylindrical, sometimes ovoid, of a constant form in some genera {Saprolegnia, Addy a) but variable in others {Pythium, Monoblepharis).
The reproduction by means of the zoosporangia is much more extensive than that by means of the oospores. Each zoosporangium contains a great number of zoospores. The mycelium is composed of long ramifying tubes, of considerable diameter, and nearly always aseptate.
The Saprolegnieae grow for the most part in water, chiefly on the dead bodies of insects. One species, Saprolegnia ferax, is notable on account of its extensive ravages on the bodies of fishes (especially salmon) and other water animals.
Suborder II.—Peronosporeae.— The Peronosporeae are very closely allied to the Saprolegnieae— the modes of reproduction both sexual and asexual being similar to those of the monoecious forms of the latter suborder. The oogonia are terminal as a rule, and the protoplasmic contents contract always into one central globule. Two forms of germination have been observed in the oospores. In Cystopus they burst and produce zoopores, and in Peronospora the usual mode of germination is by the emission of a hypha. As regards the asexually-produced spores the same rule holds. In Cystopιιs and Phytophthora they are zoosporangia, producing in the former case each the same number of zoospores as the oospores; and in Peronospora they are usually conidia, emitting hyphae on germination. Both zoospores and hyphae produce mycelia directly.
The zoosporangia of Cystopus are borne in vertical series on short, club-shaped filaments; the conidia of Peronospora in most cases, and the zoosporangia of Phytophthora, on branching, tree-like sporophores. The mycelium, which is usually septate and ramifies densely, possesses frequently haustoria of various shapes.
The Peronosporeae are parasitic on living phanerogams, the tissues of which they penetrate and destroy. The most notable example is the well-known potato-disease, Phytophthora infestans, the ravages of which are too well known to need description.
Suborder III—Mucorini.— Sexual reproduction in this suborder is effected by means of the conjugation of two apparently similar sexual cells, which as a result of their union form a zygospore. It will be sufficient to describe one typical case, viz., that of Rhizopus nigricans. The conjugating cells of this fungus are elongated, stout tubes. Where two meet, each pushes against the other a protuberance, at first cylindrical and of equal thickness. They remain closely adhering, and soon grow considerably, chiefly in thickness. At the end of each a separate cell is formed by the growth of a partition. These two cells are usually of unequal size, one as long as it is broad, the other only half as long as its breadth. The membrane which originally separated them is now perforated in the middle, and soon vanishes altogether; the two conjugating cells thus unite and form the zygospore, which increases rapidly, usually attaining a diameter of over ¾ millim. It is, as a rule, drum-shaped, the ends smooth, and the free surface clothed with wart-like protuberances. The contents are coarsely granular protoplasm, in which float drops of oil. On germination the zygospore produces a hypha (as observed in Syzygites), which by repeated dichotomous branching soon forms a new mycelium.
'½ Asexual reproduction is accomplished by sporangia similar in function, and in some degree in structure, to the corresponding organs of the two preceding suborders. They are borne terminally on special branches of the mycelial hyphae, which, like the mycelium, are aseptate up to the time of fructification. The spores produced in the sporangia germinate by the emission of a filament, which, like that produced by the zygospore, forms by dichotomous branching a new mycelium. This was the only mode of reproduction known in the Mucorini, until the researches of Professor De Bary and others brought to light the sexual form, which, however, has not yet been observed in all the species.
The Mucorini are usually to be found growing on excrement and on decaying substances; none of the species are known to cause any important disease to plants or animals.
Order II.— Hypodermiae. —No mode of sexual reproduction is known to belong to the plants of this order. They are (so far as is known) reproduced wholly by asexual spores arising by cell-division. All the species inhabit the parenchyma of living plants, through the epidermis of which the receptacles burst.
Suborder I.—Uredineae.— The life-history of the Uredineae consists of a cycle of three generations, the transition in each case being effected (so far as is at present known) by asexual spores. The cycle begins in spring with the germination of thick-walled spores, called teleutospores, borne usually in pairs at the end of sterigmata. Germination takes the form of the emission of a hypha, which rapidly (usually in two or three hours) forms a pro-mycelium, bearing three or four sporidia. These sporidia become detached, and on finding a suitable host-plant penetrate the epidermis cells by means of a germinating filament, and form a new mycelium within the parenchyma. After a few days this mycelium begins to form receptacles under the epidermis of the host, on which are borne cecidia and spermogonia. The latter appear before the former. They are small, narrownecked sacs, in which are found minute spore-like bodies, called spermatia by Tulasne, who believed them to be male organs, partly on comparative grounds and partly because he found them incapable of germinating. No female organs have been found; though it w as suggested that the spermatia stood in sexual relations to the aecidia beside which they are constantly found. Professor De Bary, however, found that the spores of aecidia, on a plant on which no trace of spermogonia or spermatia could be found, germinated exactly as under other circumstances. The aecidia are at first round or oval but on bursting basin-shaped receptacles of pseudo-parenchyma, at the base of each of which a circular, flat hymenium is formed. From this hymenium there rise erect basidia bearing in vertical series a number of spores of a round polyhedral form, and filled with protoplasm coloured red or yellow by oil. These spores on being liberated produce germ-tubes which penetrate the stomata of the next host-plant (one of the same species as that on which the teleutospores were found), and soon form another mycelium in the intercellular spaces. Again, in a few days, this mycelium forms a new kind of receptacle, the uredo. This receptacle is flat and circular, and is situated immediately under the epidermis. On it basidia bearing round or oval uredospores arise and break through the epidermis. The uredospores constantly reproduce the uredo, which is the cause of the extensive ravages of this form of the disease; on the same mycelium which produces the uredo, teleutospores are ultimately formed. These hibernate, and when spring arrives again germinate, and start the same cycle of generations.
Teleutospores aecidium-spores (accompanied by spermatia)
uredospores, and later on the same mycelium teleutospores again.
This cycle of generations is carried out on two different host plants. The uredospores and teleutospores affect the Gramineae chiefly, but the ravages of aecidia, though not so severe in their nature, extend over many species of Composite, Ranunculaceae, Leguminosae, and Labiate. Suborder II.—Ustilagineae.— The life-history of this suborder, so far as yet known, consists in the formation of asexual spores, either singly, in series, or in masses, on very slender sporophores; these germinate, and form a promycelium bearing sporidia (as in the case of the teleutospores of the Uredineae), which in turn germinate and form a mycelium bearing the same kind of spores as those with which we started. This life-history, it will be seen, is, so far as it goes, similar to that of the Uredineae. The present order resembles the preceding one also in the habit of life. They are very injurious, especially to the Graminea. The power of producing many sporidia in succession, possessed by the promycelium, tends to the plentiful distribution of the disease. These sporidia usually attack the axis of germinating plants, in which a mycelium is then developed and carried up with the growth of the plant, ultimately producing spores in the fruit and causing its destruction.
Order III.— Basidiomycetes. —The only form of reproduction known in this order is by asexual spores borne at the apex of erect basidia. These spores reproduce the plant directly without the intervention of another generation. The receptacle of the hymenium consists of interwoven hyphae, and is gelatinous, fleshy, or woody in consistency; it sometimes attains great size. The mycelium is comparatively small and floccose.
Suborder L—Tremellini. — The hymenium of this suborder bears two different kinds of basidia in different genera. In the genus Tremella the basidia are at first subglobose or quite spherical, and divided from top to bottom into four equal parts. These segments either remain united, or diverge, while they grow out to the margin of the fungus in the form of long hyphae bearing kidney-shaped spores. In Dacrymyces and Guepinia the basidia are at first claviform then divergent into two arms, bearing one reniform spore each.
Sperτnatia are often met with abundantly in many of the Tremdlini. They are produced in regular spermatophorous apparatus, and are very minute and spherical or ovoid. Like the spermatia of the Uredineae, their function is unknown.
The consistence of these plants is gelatinous, with, in some cases, a denser nucleus. They are usually to be found growing on stumps of trees and on the ground. Their shape, when they have one, is usually more or less cup-like.
Suborder II.— IIymenomycetes. — The líymenomycetes is the most widely-known group of fungi. It includes the common mushroom, to which all the species bear more or less resemblance. The familiar form is that of a pileus raised upon a stalk and bearing on its under surface the hymenium extended over gills or lamellae (Agaricini), pores (Polyporei), or teeth (Hydnaceï). From the hymenium rise the basidia* at the apex of which are usually four sterigmata bearing the spores. These spores are asexually produced, and on germinating, by emitting a hypha, give rise to a new mycelium on which the receptacle is again borne. The question of the existence of a form of sexual reproduction m the IIymenomycetes lias been fought over many times, as yet with no certain result. Among the basidia are to be seen other cells of similar shape, but of greater dimensions. called cystidia; it has been contended that these are male organs. The mycelium is nearly always underground.
The Agaricini possess an inferior hymenium spread over lamellae or gills radiating from the stalk. These are sometimes simple and sometimes branched, and attached to or distinct from the stalk. The spores vary much in colour, one colour being constant to a genus or to a subgenus. On the stems of some genera an annulus or ring may be found, as a remnant of a veil (velum partiale) which united that part of the stem with the outer edge of the cap or pileus, but was ruptured on the expansion of the latter. In certain subgenera of Agaricus (e.g., Volaria, Amanita) the whole plant is, when young, enclosed in a volva (velum universale), the remains of which may be seen in mature plants adhering to the base of the stem. In some genera, as in Amanita, both forms of veil are found together. When the stem is lateral, as in Pleurotus, it is usually very much suppressed. The species of Agarcini are usually terrestrial, many of them are edible, and a few are deadly poisons.
The Polyporei are distinguished by the hymenium (sometimes inferior, sometimes superior) extending over the surfaces of cavities or pores. In the genus Boletus the habit of an Agaric is assumed—the stem usually central, the texture almost always soft. In Polyporus the stem is usually 1 ιteral and the texture woody. The hymenophore is not easily separable. In some cases the habit of Polyporus is crust-like, the pores opening upwards, when it is called resupinate. Polypori grow usually on stumps of trees.
The IIydnacei possess an inferior or an amphigenous hymenium spread over teeth or spines. Some of the species have the form of a stalked pileus with the teeth inferior, while others resemble the resupinate Polypori, They are fleshy or corky in texture.
In the Auricularini the hymenium is confluent with the hymenophore. In form they resemble the Polypord.
The Clavarinei are distinguished by an amphigenous hymenium, scarcely distinct from the hymenophore, and reaching to the apex of the plant, which is club-shaped, or in the form of upright spines. The species are gelatinous in consistence, but become horny when dry. The surface is usually smooth at first but afterwards assumes an indented or wrinkled appearance.
Suborder III.—Gasteromycetes. —The receptacles of the Gasteromycetes are angiocarpous. They consist of an outer peridium enclosing masses of tissue which bear the hymenia. The basidia often bear as many as eight spores, which are ultimately liberated by the bursting of the peridium, either simply or by the development of special masses of tissues. The peridium of Phallus resembles the velum universale of the Agaricini in its mode of enveloping the receptacle, and the appearance it presents after bursting. Within this volva is a gelatinous stratum, then an inner peridium, then the hymenium. The bursting of the peridium or volva is caused by the elongation of a stalk on which the hymenium is elevated in a kind of pileus—as in the Agaricini. In Batarrea there also occurs a universal volva, and the hymenium is similarly elevated, but the plant in this case is of a woody consistence, and spiral vessels are found in the stalk. In Clathrus the receptacle is in the form of a globular net.
In Lycoperdon, Hymenogaster, and Nidularia the hymenium remains unelevated, and the spores are liberated by the simple bursting of the peridium.
OrderIV.— Ascomycetes. —The characteristic form of reproduction of the Ascomy celes is by ascospores formed within asci by free cell-formation. Other generations in the cycle of development form stylospores in special conceptacles called pycnidia, and conidia borne on conidiophores. The receptacles on which the ascospores are produced arise as the result of the union of sexual organs, which takes place on the mycelium. The receptacles vary very much in size and form throughout the order.
Suborder I.—Discomycetes.— The sexual organs of this suborder are formed on the mycelium and are called the carpogonium (female) and the pollinodium (male). As typical of the rest of the order the life-history of Ascobolus furfuraceus, as described by Janczewski may be chosen. Tïíq pollinodium and carpogonium are both composed of a series of short crooked cells, in the former case much thinner than in the latter. The pollinodium embraces the more remote end of the carpogonium, which is at this stage sausage-shaped, and so fertilizes it. After fertilization one of the cells of the carpogonium (usually near the middle) increases and becomes globular. It is called the ascogonium. From it proceed ascogenous hyphae on which the asci arise. The asci are flask-shaped, the base being the narrow portion, and within them the ascospores, 8 in number, are formed by free cell-formation. Between the asci, and borne on the ascogenous hyphae, are more or less numerous paraphyses which are generally regarded as abortive asci, but may serve (as Boudier affirms they do) to assist in some way the dehiscence of the asci. The hyphae of the mycelium on which the sexual organs are borne produce a dense mass of pseudo-parenchyma, which surrounds the carpogonium and forms the sterile part of the fructification.
Sexuality was first discovered in the Discomycetes by Professor De'Bary in the case of Peziza confluens, which, though it differs in details from that described as occurring in Ascobolus, agrees in all essential details with it.
Certain species of Pezizae, the mycelium of which is extensively reproduced by conidia, undergo a resting state in the form of a sclerotium. This was first observed in Peziza Fückeliana by Professor De Bary. In it conidia are produced by the mycelium before the sclerotia. The sclerotia, which are formed without the occurrence of any sexual process, so far as has been observed, consist of densely packed hyphae enclosed by a pseudo-parenchymatous rind. Sometimes these germinate shortly after their formation, and produce a mycelium which bears conidia again; but if germination be delayed for a month or two, the characteristic basin-shaped hymenium of Peziza, with asci and ascospores, is formed.
Spermatia are found in this as in other orders. They are borne in spermogonia, similar to those of the Uredineae, and were long believed to be incapable of germination. Μ. Cornu, however, has recently stated that he caused them to germinate under artificial conditions, and to produce a mycelium like the conidia.
In Peziza and the genera closely allied to it, the ascogenous receptacle is basin-shaped, with the hymenium on the inner surface of the basin; but in other genera it takes the form of clubs or stalks of considerable size with the hymenium on the outer surface (as in Geoglossum, Spathu-laria, Helvella, Morchella, <tc.).
The species of Morchella and Helvella are, as a rule, esculent; but none of the other Discomycetes have ever obtained any reputation in this direction.
Suborder II.— Erysiphea ι . — In this suborder the species follow two types in their mode of sexual reproduction, viz., Erysiphe and Eurotium.
The mycelium of Erysiphe creeps over the surface of its host plant, through the epidermis of which it sends down numerous haustoria. Both the conidia and the sexually produced fruits are borne on the same mycelium. The conidia occur in vertical order at the end of unbranched conidiophores. These conidia reproduce the mycelium directly. The mode of sexual reproduction resembles that of the Discomycetes. The carpogonium is more or less globular in shape, and is fertilized by a pollinodium of one or more branches. The carpogonium is at first represented by one cell, but after fertilization a transverse wall divides it into two cells, the inferior one of which must be regarded as an ascogenous hypha. The superior one becomes the ascus, which in most cases contains 8 spores. In a few other forms several asci are formed by the carpogonium.
The species of Eurotium— e.g., E. repens and E. (Aspergillus) glaucus — agree in the more striking details of their life-history with those of Erysiphae. The mycelium may be found as a fine flocculent mass on the surfaces of most putrefying organic matter. The usual and most extensive mode of reproduction is by the conidia, which are formed in great abundance at the apex of the conidiophores. These germinate and grow under most varied conditions, which fact, coupled with their plentiful production, explains the general distribution of the fungus. Subsequently the sexual organs arise on the same mycelium. The carpogonium is the end of a mycelial hypha wound up in the form of a corkscrew, with a tranverse septum at each turn of the screw. From the lowest turn two tubes sprout and grow up on the outside of the carpogonium; one a!ways grows more rapidly than the other, and reaches the top of the carpogonium, which it fertilizes. This is the pollinodium. Other cells then grow out from the bases of both organs and envelop them. After fertilization the carpogonium divides into several cells from which the ascogenous hyphae arise. The asci contain ascospores which germinate as in the other Erysipheae. The whole fructification is called the perithecium. Suborder HI.—Tuberaceae.— The mycelium of the Tuberaceae is in most cases small in comparison with the fructification. This fructification consists usually of a large subterranean tuberous body, possessing a thick wall of pseudoparenchyma, and enclosing a dense mass of hyphae, among which the ascogenous filaments produce the asci embedded in sterile paraphyses. Conidia are known only in the case of Pénicillium glaucum, a fungus which, from its common occurrence, and its being well-known in all its stages, may be chosen as a type of the suborder. Its mycelium inhabits almost any organic substance, and produces on erect conidiophores long chains of conidia in very great abundance. It is only in darkness that (as in the other Tuberaceae) the sexually produced form of fructification arises. The sexual organs resemble in a very high degree those of Eurotium (see preceding suborder), but the development of the fructification after the ascogonium has been fertilized is totally different from the corresponding process. After the ascogonium has begun to germinate, the growth of the enveloping hyphae so hinders this process that it is forced to rest in a sclerotioid state. If germination, however, be encouraged by artificial means, the ascogenous hyphae force their way out and form asci, in each of which there are 8 ascospores. These spores, on germinating, produce a mycelium which bears conidia. If the germination of the sclerotia be delayed so long that the ascogenous hyphae lose the power of producing asci, the enveloping filaments give rise to the conidial form of fructification. The structure of those sclerotia is so similar to that of the well-known tuberous fructifications of the Tuberaceae, that Brefeld, who discovered them, classes Pénicillium with this suborder, in spite of the very strong resemblance of the sexual organs to those of Eurotium. In no other species of Tuberaceae has this life-history been observed.
Suborder IV.—-Pyrenomycetes.— Tlιe Pyrenomycetes produce their asci within round or flask-shaped perithecia, with walls of pseudo-parenchyma. The asci contain, as a rule, 8 spores. In some cases the perithecium is open at first, but in others the neck, closed during the earlier stage, forms subsequently a canal through which the spores escape. In t∫ιe case of the Sphaeriae simplices, the perithecia arise on a very fine mycelium, and according to Woronin and others are the result of a sexual act. In Xylaria and allied genera, however, the perithecia are formed on sometimes very large club or basin shaped bodies, consisting of dense masses of tissue, which, according to some, are simply the receptacles, and according to others, bearers of sexual organs, the union of which gives rise to the perithecia. Analogy leads to regarding them as receptacles. Conidia are formed not only on the mycelium but also on the stroma, and even occasionally on the hyphae composing the wall of the perithecium. Spermogonia and pycnidia are other conceptacles which give rise to asexual organs of reproduction, called respectively spermatia and stylospores. It was urged with much show of probability that these were parasitic bodies; but the recent researches of Dr Bauke on the pycnidia and Μ. Cornu on the spermatia seem to disprove this view. Μ. Cornu states that he caused spermatia to germinate and reproduce the mycelium of the species to which they belonged. It will be seen, however, that in the next suborder (Lichenes) the analogous spermatia act as male organs,—a function which not only precludes the possibility of their parasitic nature, but does not agree well with Μ. Cornu’s (so far as we know) unconfirmed views. In Claυiceps purpurea (ergot), which attacks the young ovary of rye, the mycelium first bears conidia embedded in a mucous secretion; this is called the sphacelia stage. The mycelium, however, soon permeates the ovary and forms a hard sclerotium—the ergot stage. After undergoing a period of rest, usually from summer to spring, but varying in length, the sclerotium on falling on damp ground pushes out small stalks with a rounded head in which numerous flask-shaped, wall-less perithecia arise. These perithecia bear as usual asci containing ascospores. The ascospores, on germinating, and finding their usual host—the rye, or some nearly related grass, give rise again to the sphacelia, which closes the cycle.
This suborder, like the Dìscomycetes, contains a great number of forms, many of which are known in only one, viz., the perithecium-bearing stage,—the other phases probably being known by other names as distinct genera and species. The Pyrenomycetes grow either on dead organic matter or on the bodies of living plants.
Suborder V.— Lichenes. — Until recently, and before their true nature was understood, the Lichenes were treated as constituting a separate class of cellular cryptogams or Thallophyta. The researches of Schwendener, Stahl, De Bary, Bornet, and others have proved that these consist of a fungal Ascomycetous element parasitic on an algal element. The algal element belongs to the lower orders of Algae and acts as the nourisher of the fungal element. The funga] element is reproduced by Ascomycetous reproductive organs, and the algal element, which in a free state is capable of independently subsisting, is reproduced in the manner characteristic of the order of Algae to which it belongs. We have to do here with the life-history of the fungal portion only, but illustration will be given of its relations with its host.
Though sexuality is not known to exist generally in the Lichenes, it has been so satisfactorily proved in the case of the Collemaceae by Dr Stahl that it may be concluded that investigation only is necessary to bring fresh cases to light. In the Collemaceae the male organs of reproduction (the sp>ermatia) are formed within receptacles called spermogonia (similar organs have been described [as occurring in the Uredineae, &c.), and though not possessing the power of spontaneous motion, reach the female organ (trichogyne) by the agency of water or the atmosphere. The spermatia consist of one simple minute cell; the trichogynes are of a more complicated structure, and may be described as consisting of a unicellular organ of conception, a conductive canal, and an ascogonium, consisting of a coiled hypha of several cells. The point of the trichogyne emerges from the surface of the thallus, and the spermatia ou coming in contact become united with it by a small tube through which the contents of the male organs fertilize the trichogyne. After fertilization the cells of the ascogonium increase in number and size, and the ascogenous hyphae spring from the original coil and bear the characteristic asci in which the ascospores are formed.
The relations between the fungal and the algal elements may be illustrated by the following instance from Dr Stahl’s Beiträge zur Entwickelungsgeschichte der Flechten. The Algae were formerly considered organs of the fungal portion, and received the name of gonidia. A smaller form of gonidia, called the hymenial-gonidia. j occurs in interstitial spaces of the apothecia of many Lichens; these hymenial-gonidia are the offspring of the ordinary gonidia (the thallus-gonidia), and have been carried up in the hymenium by the growth of its hyphae. When the ascospores are emitted from the apothecia, the hymenial-gonidia are cast out also, and falling in the neighbourhood of the ascospores are, many of them, enveloped by the germinating filaments proceeding from the spores, when the conditions are favourable for growth. Along with the growth of the hyphae, these hymenial-gonidia increase in size, and ultimately act as the thallus-gonidia of the new Lichen. This process has been observed in Dermatocarpon Schaereri and Polyblastia rugulosa. When this discovery was made by Dr Stahl, he found growing beside the Dermatocarpon a species of Thelidium, the gonidia of which appeared to belong to the same species of Alga as those of the Dermatocarpon. He isolated, under favourable conditions for growth, the spores of Thaelidium and the hymenial-gonidia of Dermatocarpon, and soon obtained the thallus of Thelidium complete as regards gonidia and fructification. This experiment, by proving that the same species of Alga (in this case a species of Pleurococcuf) served as the gonidia of two totally different fungi, also strongly supports the above views as to the dual nature of the elements composing the Lichen. These views, though supported by the most eminent botanists and backed by incontestable facts, are still occasionally the subject of attack by lichenologists.
The suborder Lichenes contains a greater number of species than any other suborder or order of fungi, but it is probable that excessive subdivision has given rise to many. Lichens grow chiefly in exposed situations, such as the bark of trees and rocks, and are very generally distributed throughout the globe. They vary much in size and form, but are generally of a foliaceous or encrusting habit. They form a large proportion of the vegetation of alpine and polar regions. Their economic and medicinal properties are in many cases of importance.
Order V.— Myxomycètes. —In the first stage of their life-history the Myxomycètes are mobile organisms, differing so strongly from any state of any other vegetable that it was proposed by Professor De Bary to place them among amoeboid animal organisms. In this stage, where one would expect a thallus of hyphae, a mobile plasmodium is found, which in habit of life greatly resembles animal organisms. In appearance it is slimy or creamy, and consists of numerous anastomosing net-like channels, through which there is conducted with more or less rapidity a current of protoplasmic matter containing many foreign bodies, such as particles of colouring matter of different natures, starch granules, diatoms, spores of fungi, &c. These channels are not bounded by any definite membrane, and the direction is frequently changed, probably for the purpose of gathering nourishment. Where one or more individuals are situated near each other these plasmodia occasionally unite (this has been observed between two different species). These mobile masses ultimately, usually after undergoing division, are transformed into motionless fruits, in some cases of regular form (sporangia), and in others of irregular (plasmodiocarp). Compound fruits called athalia i of regular or irregular form, either naked or enclosed by a membrane (cortex), are produced externally on definite sporophores by cell-division, or within the fruit by free-cell formation. On germinating, the contents of the spores escape either in the form of a zoospore with a nucleus, vacuole, and long cilia, or of an amoeboid, and these zoospores or amaeboids soon aggregate and form mobile plasmodia.
Taking the two generations in their life-history, it will be found that the fructification has probably greater claims to a fungal nature than the plasmodium has to an animal. They have, therefore, been retained in the vegetable king-dont by the majority of botanists,— whether justly or not remains to be determined by future research.
Order VI.— Schizomycetes. —In the Schizomycetes, the usual and apparently most common form of reproduction is by simple segmentation. In several forms, however, reproduction of a higher type has been observed. Au instance of this is to be found in Bacillus anthracis — the cause of splenic fever—the life-history of which, according to Ewart, Koch, and others, is as follows. At first the Bacilli consist of motionless hyaline rods capable of segmentation, which after a short time pass through a motile phase lasting usually several hours. After settling down these rods elongate considerably in a short time; if the temperature be favourable a rod may increase in five hours to from 80 or 100 times its original length. The filaments usually become interwoven like mycelial hyphae, and are in most cases irregular in their course. Within them spores are soon formed by free cell-formation, each spore being separated from its neighbour by a transverse septum. At this stage the filaments decay more or less rapidly and set free the oval spores, which are, from Cohn’s measurement, not more than 7 √ 0 ⅞∙ c ∙ to ^∕ σ ⅞- δ ∙ inch in their greatest diameter. According to Koch these spores directly elongate into filaments, but Ewart has more recently observed that they divide into four sporules, each of which germinates by the production of a filament. These filaments become motionless rods such as those from which we started.
In the classification of this order much confusion exists from the meagreness of our knowledge of the life-history of its members. Organisms described as Micrococcus, Bacterium, and Bacillus are apparently in many cases different phases of the same life-history. Much attention has been paid to their influence on diseases of men and animals, from their frequent occurrence on mucous surfaces, on wounds, and elsewhere. An extensive literature has arisen on this subject, but its interest is far more medical than botanical. Whether these organisms are the concomitants or the causes of diseases in men and animals has not often been decided, and is still much debated,—a source of frequent error being the confusion of debris of various kinds with Bacteria, &c. “Spontaneous generation” has also been attributed to them, but there has certainly not been anything like proof to support this assertion.
The following are the most important works of reference on this subject :—
Morphology and Physiology.— A. de Bary, Morphologic und Physiologic dor Pilze, Flechten, und Myxomyccten, Leipsic, 1866; Id., Die Mycctozoen Schleimpilzc, Leipsic, 1864; Id., Untersuchungen über die Brandpilze, Berlin, 1853; Id., “Recherches sur les Champignons parasites,” in Ann. Sc. not., tom. xx., 4e series; Id., Die Fruchtentwickelung der Ascomyceten, Leipsic, 1863; Id., Zur Kenntniss der Mucorincn und Peronosporeen, Frankfort, 1865; De Bary and Woronin, Beiträge sur Morphologie aud Physiologie der Pilze, Frankfort, 1864; M. J. Berkeley, Introduction to Cryptogamie Botany, London, 1857; H. Bonorden, Handbuch der allgemeinen Mykologie, Stuttgart, 1851; 0. Brefeld, Botanische Untersuchungen über Schimmelpilze, Leipsic, 1872-77; M. Cornu, “Monographie des Saprolegniees, ,, in Ann. Sc. not., 1872; C. Nägeli, Die niederen Pilze in ihrer Beziehungen zu der Infectionskrankheiten und der Gesundheitspflege, Munich, 1877; S. Schwendener, Untersuchungen über den Flechtcnthallus, Leipsic, 1860-1868; E. Stahl, Beiträge zur Entwickelungsgcschichte der Flechten, Leipsic, 1878; Louis René and Charles Tulasno, Selecta fungorum carpologia, Paris, 1861-65; Van Tieghem, “Mémoires sur les Mucorinées,” in Ann. Se. nat. The student is also referred to the files of the Botanische Zeitung, the Annales des Sciences naturelles, Pringsheim’s Jahr- bûcher, and Cohn’s Beiträge zur Biologie der Pflanzen, for excellent and important papers, far too numerous to be quoted here.
Systematic Mycology. — M. C. Cooke, Handbook of British Fungi, I√ondon, 1871; A. Corda, leones Fungorum hucusque cognitorum, 1 ragιιβ, 1837-42; M. J. Berkeley, Outlines of British Funqoloqy, London, I860; P. Bulliard, Herbier de la France, Paris, 1780-98; KM. Fries, Systema Mycologicum, Grcifswalde, 1821-32; Id., Hymcnomycetes Europaei, Upsala, 1874; Id., Icmics selectas Hymeno- w∙ ccz v nondum dclineatorum ; L. Fückel, Symbolas Mycòlogicae, w lesbaden, 1869-75; L. Rabenhorst, Deutschlands Kryptogamen- Flora, Leipsic, 1844—48; J. Rostafinski, A Monograph of the Myxomycètes in the Polish language (partly translated into English By M. C. Cooke); J. Sowerby, Coloured Figures of English Fungi, &c., London, 1797-1815; L. R. and C. Tulasne, Fungi hypogaei, Paris, 1863; D. R. Visiani, I funghi cΓ Italia, Genoa, 1834; C. Vittadini, Monographic, Tuberacearum, Milan, 1831; Id., Monographia Lycoperdineorum, Turin, 1843.
