A work of this kind could not be considered complete without some account of the systematic arrangement or classification which these plants receive at the hands of botanists. It would hardly avail to enter too minutely into details, yet sufficient should be attempted to enable the reader to comprehend the value and relations of the different groups into which fungi are divided. The arrangement generally adopted is based upon the “Systema Mycologicum” of Fries, as modified to meet the requirements of more recent microscopical researches by Berkeley in his “Introduction,”[A] and adopted in Lindley’s “Vegetable Kingdom.” Another arrangement was proposed by Professor de Bary,[B] but it has never met with general acceptance.

In the arrangement to which we have alluded, all fungi are divided into two primary sections, having reference to the mode in which the fructification is produced. In one section, the spores (which occupy nearly the same position, and perform similar functions, to the seeds of higher plants) are naked; that is, they are produced on spicules, and are not enclosed in cysts or capsules. This section is called Sporifera, or spore-bearing, because, by general consent, the term spore is limited in fungi to such germ-cells as are not produced in cysts. The second section is termed Sporidiifera, or sporidia-bearing, because in like manner the term sporidia is limited to such germ-cells as are produced in cells or cysts. These cysts are respectively known as sporangia, and asci or thecÆ. The true meaning and value of these divisions will be better comprehended when we have detailed the characters of the families composing these two divisions.

First, then, the section Sporifera contains four families, in two of which a hymenium is present, and in two there is no proper hymenium. The term hymenium is employed to represent a more or less expanded surface, on which the fructification is produced, and is, in fact, the fruit-bearing surface. When no such surface is present, the fruit is borne on threads, proceeding direct from the root-like filaments of the mycelium, or an intermediate kind of cushion or stroma. The two families in which an hymenium is present are called Hymenomycetes and Gasteromycetes. In the former, the hymenium is exposed; in the latter, it is at first enclosed. We must examine each of these separately.

The common mushroom may be accepted, by way of illustration, as a type of the family Hymenomycetes, in which the hymenium is exposed, and is, in fact, the most noticeable feature in the family from which its name is derived. The pileus or cap bears on its under surface radiating plates or gills, consisting of the hymenium, over which are thickly scattered the basidia, each surmounted by four spicules, and on each spicule a spore. When mature, these spores fall freely upon the ground beneath, imparting to it the general colour of the spores. But it must be observed that the hymenium takes the form of gill-plates in only one order of Hymenomycetes, namely, the Agaricini; and here, as in Cantharellus, the hymenium is sometimes spread over prominent veins rather than gills. Still further divergence is manifest in the Polyporei, in which order the hymenium lines the inner surface of pores or tubes, which are normally on the under side of the pileus. Both these orders include an immense number of species, the former more or less fleshy, the latter more or less tough and leathery. There are still other forms and orders in this family, as the Hydnei, in which the hymenium clothes the surface of prickles or spines, and the Auricularini, in which the hymenium is entirely or almost even. In the two remaining orders, there is a still further divergence from the mushroom form. In the one called Clavariei, the entire fungus is either simply cylindrical or club-shaped, or it is very much branched and ramified. Whatever form the fungus assumes, the hymenium covers the whole exposed surface. In the Tremellini, a peculiar structure prevails, which at first seems to agree but little with the preceding. The whole plant is gelatinous when fresh, lobed and convolute, often brain-like, and varying in size, according to species, from that of a pin’s head to that of a man’s head. Threads and sporophores are imbedded in the gelatinous substance,[C] so that the fertile threads are in reality not compacted into a true hymenium. With this introduction we may state that the technical characters of the family are thus expressed:—

Hymenium free, mostly naked, or, if enclosed at first, soon exposed; spores naked, mostly quaternate, on distinct spicules = Hymenomycetes.

In this family some mycologists believe that fungi attain the highest form of development of which they are capable, whilst others contend that the fructification of the Ascomycetes is more perfect, and that some of the noblest species, such as the pileate forms, are entitled to the first rank. The morel is a familiar example. Whatever may be said on this point, it is incontrovertible that the noblest and most attractive, as well as the largest, forms are classed under the Hymenomycetes.

In Gasteromycetes, the second family, a true hymenium is also present, but instead of being exposed it is for a long time enclosed in an outer peridium or sac, until the spores are fully matured, or the fungus is beginning to decay. The common puff-ball (Lycoperdon) is well known, and will illustrate the principal feature of the family. Externally there is a tough coat or peridium, which is at first pale, but ultimately becomes brown. Internally is at first a cream-coloured, then greenish, cellular mass, consisting of the sinuated hymenium and young spores, which at length, and when the spores are fully matured become brownish and dusty, the hymenium being broken up into threads, and the spores become free. In earlier stages, and before the hymenium is ruptured, the spores have been found to harmonize with those of Hymenomycetes in their mode of production, since basidia are present surmounted each by four spicules, and each spicule normally surmounted by a spore.[D] Here is, therefore, a cellular hymenium bearing quaternary spores, but, instead of being exposed, this hymenium is wholly enclosed within an external sac or peridium, which is not ruptured until the spores are fully matured, and the hymenium is resolved into threads, together forming a pulverulent mass. It must, however, be borne in mind, that in only some of the orders composing this family is the hymenium thus evanescent, in others being more or less permanent, and this has led naturally enough to the recognition of two sub-families, in one of which the hymenium is more or less permanent, thus following the Hymenomycetous type; and in the other, the hymenium is evanescent, and the dusty mass of spores tends more towards the Coniomycetes, this being characterized as the coniospermous (or dusty-spored) sub-family.

The first sub-family includes, first of all, the HypogÆi, or subterranean species. And here again it becomes necessary to remind the reader that all subterranean fungi are not included in this order, inasmuch as some, of which the truffle is an example, are sporidiiferous, developing their sporidia in asci. To these allusion must hereafter be made. In the HypogÆi, the hymenium is permanent and convoluted, leaving numerous minute irregular cavities, in which the spores are produced on sporophores. When specimens are very old and decaying, the interior may become pulverulent or deliquescent. The structure of subterranean fungi attracted the attention of Messrs. Tulasne, and led to the production of a splendid monograph on the subject.[E] Another order belonging to this sub-family is the Phalloidei, in which the volva or peridium is ruptured whilst the plant is still immature, and the hymenium when mature becomes deliquescent. Not only are some members of this order most singular in appearance, but they possess an odour so foetid as to be unapproached in this property by any other vegetable production.[F] In this order, the inner stratum of the investing volva is gelatinous. When still young, and previous to the rupture of the volva, the hymenium presents sinuous cavities in which the spores are produced on spicules, after the manner of Hymenomycetes.[G] Nidulariacei is a somewhat aberrant order, presenting a peculiar structure. The peridium consists of two or three coats, and bursts at the apex, either irregularly or in a stellate manner, or by the separation of a little lid. Within the cavity are contained one or more secondary receptacles, which are either free or attached by elastic threads to the common receptacle. Ultimately the secondary receptacles are hollow, and spores are produced in the interior, borne on spicules.[H] The appearance in some genera as of a little bird’s-nest containing eggs has furnished the name to the order.

The second sub-family contains the coniospermous puff-balls, and includes two orders, in which the most readily distinguishable feature is the cellular condition of the entire plant, in its earlier stages, in the Trichogastres, and the gelatinous condition of the early state of the Myxogastres. Both are ultimately resolved internally into a dusty mass of threads and spores. In the former, the peridium is either single or double, occasionally borne on a stem, but usually sessile. In Geaster, the “starry puff-balls,” the outer peridium divides into several lobes, which fall back in a stellate manner, and expose the inner peridium, like a ball in the centre. In Polysaccum, the interior is divided into numerous cells, filled with secondary peridia. The mode of spore-production has already been alluded to in our remarks on Lycoperdon. All the species are large, as compared with those of the following sub-family, and one species of Lycoperdon attains an enormous size. One specimen recorded in the “Gardener’s Chronicle” was three feet four inches in circumference, and weighed nearly ten pounds. In the Myxogastres, the early stage has been the subject of much controversy. The gelatinous condition presents phenomena so unlike anything previously recorded in plants, that one learned professor[I] did not hesitate to propose their exclusion from the vegetable, and recognition in the animal, kingdom as associates of the Gregarines. When mature, the spores and threads so much resemble those of the Trichogastres, and the little plants themselves are so veritably miniature puff-balls, that the theory of their animal nature did not meet with a ready acceptance, and is now virtually abandoned. The characters of the family we have thus briefly reviewed are tersely stated, as—

Hymenium more or less permanently concealed, consisting in most cases of closely-packed cells, of which the fertile ones bear naked spores on distinct spicules, exposed only by the rupture or decay of the investing coat or peridium = Gasteromycetes.

We come now to the second section of the Sporifera, in which no definite hymenium is present. And here we find also two families, in one of which the dusty spores are the prominent feature, and hence termed Coniomycetes; the other, in which the threads are most noticeable, is Hyphomycetes. In the former of these, the reproductive system seems to preponderate so much over the vegetative, that the fungus appears to be all spores. The mycelium is often nearly obsolete, and the short pedicels so evanescent, that a rusty or sooty powder represents the mature fungus, infesting the green parts of living plants. This is more especially true of one or two orders. It will be most convenient to recognize two artificial sub-families for the purpose of illustration, in one of which the species are developed on living, and in the other on dead, plants. We will commence with the latter, recognizing first those which are developed beneath the cuticle, and then those which are superficial. Of the sub-cuticular, two orders may be named as the representatives of this group in Britain, these are the SphÆronemei, in which the spores are contained in a more or less perfect perithecium, and the Melanconiei, in which there is manifestly none. The first of these is analogous to the SphÆriacei of Ascomycetous fungi, and probably consists largely of spermogonia of known species of SphÆria, the relations of which have not hitherto been traced. The spores are produced on slender threads springing from the inner wall of the perithecium, and, when mature, are expelled from an orifice at the apex. This is the normal condition, to which there are some exceptions. In the Melanconiei, there is no true perithecium, but the spores are produced in like manner upon a kind of stroma or cushion formed from the mycelium, and, when mature, are expelled through a rupture of the cuticle beneath which they are generated, often issuing in long gelatinous tendrils. Here, again, the majority of what were formerly regarded as distinct species have been found, or suspected, to be forms of higher fungi. The Torulacei represent the superficial fungi of this family, and these consist of a more or less developed mycelium, which gives rise to fertile threads, which, by constriction and division, mature into moniliform chains of spores. The species mostly appear as blackish velvety patches or stains on the stems of herbaceous plants and on old weathered wood.

Much interest attaches to the other sub-family of Coniomycetes, in which the species are produced for the most part on living plants. So much has been discovered during recent years of the polymorphism which subsists amongst the species in this section, that any detailed classification can only be regarded as provisional. Hence we shall proceed here upon the supposition that we are dealing with autonomous species. In the first place, we must recognize a small section in which a kind of cellular peridium is present. This is the Æcidiacei, or order of “cluster cups.” The majority of species are very beautiful objects under the microscope; the peridia are distinctly cellular, and white or pallid, produced beneath the cuticle, through which they burst, and, rupturing at the apex, in one genus in a stellate manner, so that the teeth, becoming reflexed, resemble delicate fringed cups, with the orange, golden, brown, or whitish spores or pseudospores nestling in the interior.[J] These pseudospores are at first produced in chains, but ultimately separate. In many cases these cups are either accompanied or preceded by spermogonia. In two other orders there is no peridium. In the CÆomacei, the pseudospores are more or less globose or ovate, sometimes laterally compressed and simple; and in PucciniÆi, they are elongated, often subfusiform and septate. In both, the pseudospores are produced in tufts or clusters direct from the mycelium. The CÆomacei might again be subdivided into Ustilagines[K] and Uredines.[L] In the former, the pseudospores are mostly dingy brown or blackish, and in the latter more brightly coloured, often yellowish. The Ustilagines include the smuts and bunt of corn-plants, the Uredines include the red rusts of wheat and grasses. In some of the species included in the latter, two forms of fruit are found. In Melampsora, the summer pseudospores are yellow, globose, and were formerly classed as a species of Lecythea, whilst the winter pseudospores are brownish, elongated, wedge-shaped by compression, and compact. The PucciniÆi[M] differ primarily in the septate pseudospores, which in one genus (Puccinia) are uniseptate; in Triphragmium, they are biseptate; in Phragmidium, multiseptate; and in Xenodochus, moniliform, breaking up into distinct articulations. It is probable that, in all of these, as is known to be the case in most, the septate pseudospores are preceded or accompanied by simple pseudospores, to which they are mysteriously related. There is still another, somewhat singular, group usually associated with the PucciniÆi, in which the septate pseudospores are immersed in gelatin, so that in many features the species seem to approach the Tremellini. This group includes two or three genera, the type of which will be found in Podisoma.[N] These fungi are parasitic on living junipers in Britain and North America, appearing year after year upon the same gouty swellings of the branches, in clavate or horn-shaped gelatinous processes of a yellowish or orange colour. Anomalous as it may at first sight appear to include these tremelloid forms with the dust-like fungi, their relations will on closer examination be more fully appreciated, when the form of pseudospores, mode of germination, and other features are taken into consideration, especially when compared with Podisoma Ellisii, already alluded to. This family is technically characterized as,—

Distinct hymenium none. Pseudospores either solitary or concatenate, produced on the tips of generally short threads, which are either naked or contained in a perithecium, rarely compacted into a gelatinous mass, at length producing minute spores = Coniomycetes.

The last family of the sporifera is Hyphomycetes, in which the threads are conspicuously developed. These are what are more commonly called “moulds,” including some of the most elegant and delicate of microscopic forms. It is true of many of these, as well as of the Coniomycetes, that they are only conidial forms of higher fungi; but there will remain a very large number of species which, as far as present knowledge extends, must be accepted as autonomous. In this family, we may again recognize three subdivisions, in one of which the threads are more or less compacted into a common stem, in another the threads are free, and in the third the threads can scarcely be distinguished from the mycelium. It is this latter group which unites the Hyphomycetes with the Coniomycetes, the affinities being increased by the great profusion with which the spores are developed. The first group, in which the fertile threads are united so as to form a compound stem, consists of two small orders, the Isariacei and the Stilbacei, in the former of which the spores are dry, and in the latter somewhat gelatinous. Many of the species closely imitate forms met with in the Hymenomycetes, such as Clavaria; and, in the genus Isaria, it is almost beyond doubt that the species found on dead insects, moths, spiders, flies, ants, &c., are merely the conidiophores of species of Torrubia.[O]

The second group is by far the largest, most typical, and attractive in this family. It contains the black moulds and white moulds, technically known as the Dematiei and the Mucedines. In the first, the threads are more or less corticated, that is, the stem has a distinct investing membrane, which peels off like a bark; and the threads, often also the spores, are dark-coloured, as if charred or scorched. In many cases, the spores are highly developed, large, multiseptate, and nucleate, and seldom are spores and threads colourless or of bright tints. In the Mucedines, on the contrary, the threads are never coated, seldom dingy, mostly white or of pure colours, and the spores have less a tendency to extra development or multiplex septation. In some genera, as in Peronospora for instance,[P] a secondary fruit is produced in the form of resting spores from the mycelium; and these generate zoospores as well as the primary spores, similar to those common in AlgÆ. This latter genus is very destructive to growing plants, one species being the chief agent in the potato disease, and another no less destructive to crops of onions. The vine disease is produced by a species of Oidium, which is also classed with Mucedines, but which is really the conidiiferous form of Erysiphe. In other genera, the majority of species are developed on decaying plants, so that, with the exception of the two genera mentioned, the Hyphomycetes exert a much less baneful influence on vegetation than the Coniomycetes. The last section, including the Sepedoniei, has been already cited as remarkable for the suppression of the threads, which are scarcely to be distinguished from the mycelium; the spores are profuse, nestling on the floccose mycelium; whilst in the Trichodermacei, the spores are invested by the threads, as if enclosed in a sort of false peridium. A summary of the characters of the family may therefore be thus briefly expressed:—

Filamentous; fertile threads naked, for the most part free or loosely compacted, simple or branched, bearing the spores at their apices, rarely more closely packed, so as to form a distinct common stem = Hyphomycetes.

Having thus disposed of the Sporifera, we must advert to the two families of Sporidiifera. As more closely related to the Hyphomycetes, the first of these to be noticed is the Physomycetes, in which there is no proper hymenium, and the threads proceeding from the mycelium bear vesicles containing an indefinite number of sporidia. The fertile threads are either free or only slightly felted. In the order Antennariei, the threads are black and moniliform, more or less felted, bearing irregular sporangia. A common fungus named Zasmidium cellare, found in cellars, and incrusting old wine bottles, as with a blackened felt, belongs to this order. The larger and more highly-developed order, Mucorini, differs in the threads, which are simple or branched, being free, erect, and bearing the sporangia at the tips of the thread, or branches. Some of the species bear great external resemblance to Mucedines until the fruit is examined, when the fructifying heads, commonly globose or ovate, are found to be delicate transparent vesicles, enclosing a large number of minute sporidia; when mature, the sporangia burst and the sporidia are set free. In some species, it has long been known that a sort of conjugation takes place between opposite threads, which results in the formation of a sporangium.[Q] None of these species are destructive to vegetation, appearing only upon decaying, and not upon living, plants. A state approaching putrescence seems to be essential to their vigorous development. The following characters may be compared with those of the family preceding it:—

Filamentous, threads free or only slightly felted, bearing vesicles, which contain indefinite sporidia = Physomycetes.

In the last family, the Ascomycetes, we shall meet with a very great variety of forms, all agreeing in producing sporidia contained in certain cells called asci, which are produced from the hymenium. In some of these, the asci are evanescent, but in the greater number are permanent. In Onygenei, the receptacle is either club-shaped or somewhat globose, and the peridium is filled with branched threads, which produce asci of a very evanescent character, leaving the pulverulent sporidia to fill the central cavity. The species are all small, and singular for their habit of affecting animal substances, otherwise they are of little importance. The Perisporiacei, on the other hand, are very destructive of vegetation, being produced, in the majority of cases, on the green parts of growing plants. To this order the hop mildew, rose mildew, and pea mildew belong. The mycelium is often very much developed, and in the case of the maple, pea, hop, and some others, it covers the parts attacked with a thick white coating, so that from a distance the leaves appear to have been whitewashed. Seated on the mycelium, at the first as little orange points, are the perithecia, which enlarge and become nearly black. In some species, very elegant whitish appendages radiate from the sides of the perithecia, the variations in which aid in the discrimination of species. The perithecia contain pear-shaped asci, which spring from the base and enclose a definite number of sporidia.[R] The asci themselves are soon dissolved. Simultaneously with the development of sporidia, other reproductive bodies are produced direct from the mycelium, and in some species as many as five different kinds of reproductive bodies have been traced. The features to be remembered in Perisporiacei, as forming the basis of their classification, are, that the asci are saccate, springing from the base of the perithecia, and are soon absorbed. Also that the perithecia themselves are not perforated at the apex.

The four remaining orders, though large, can be easily characterized. In Tuberacei, all the species are subterranean, and the hymenium is mostly sinuated. In Elvellacei, the substance is more or less fleshy, and the hymenium is exposed. In Phacidiacei, the substance is hard or leathery, and the hymenium is soon exposed. And in SphÆriacei, although the substance is variable, the hymenium is never exposed, being enclosed in perithecia with a distinct opening at the apex, through which the mature spores escape. Each of these four orders must be examined more in detail. The Tuberacei, or subterranean Ascomycetes, are analogous to the HypogÆi of the Gasteromycetes. The truffle is a familiar and highly prized example. There is a kind of outer peridium, and the interior consists of a fleshy hymenium, more or less convoluted, sometimes sinuous and confluent, so as to leave only minute elongated and irregular cavities, and sometimes none at all, the two opposing faces of the hymenium meeting and coalescing.[S] Certain privileged cells of the hymenium swell, and ultimately become asci, enclosing a definite number of sporidia. The sporidia in many cases are large, reticulated, echinulate or verrucose, and mostly somewhat globose. In the genus Elaphomyces, the asci are more than commonly diffluent.

The Elvellacei are fleshy in substance, or somewhat waxy, sometimes tremelloid. There is no peridium, but the hymenium is always exposed. There is a great variety of forms, some being pileate, and others cup-shaped, as there is also a great variation in size, from the minute Peziza, small as a grain of sand, to the large Helvella gigas, which equals in dimensions the head of a child. In the pileate forms, the stroma is fleshy and highly developed; in the cup-shaped, it is reduced to the external cells of the cup which enclose the hymenium. The hymenium itself consists of elongated fertile cells, or asci, mixed with linear thread-like barren cells, called paraphyses, which are regarded by some authors as barren asci. These are placed side by side in juxtaposition with the apex outwards. Each ascus contains a definite number of sporidia, which are sometimes coloured. When mature, the asci explode above, and the sporidia may be seen escaping like a miniature cloud of smoke in the light of the mid-day sun. The disc or surface of the hymenium is often brightly coloured in the genus Peziza; tints of orange, red, and brown having the predominance.

In Phacidiacei, the substance is hard and leathery, intermediate between the fleshy Elvellacei and the more horny of the SphÆriacei. The perithecia are either orbicular or elongated, and the hymenium soon becomes exposed. In some instances, there is a close affinity with the Elvellacei, the exposed hymenium being similar in structure, but in all the disc is at first closed. In orbicular forms, the fissure takes place in a stellate manner from the centre, and the teeth are reflexed. In the Hysteriacei, where the perithecia are elongated, the fissure takes place throughout their length. As a rule, the sporidia are more elongated, more commonly septate, and more usually coloured, than in Elvellacei. Only a few solitary instances occur of individual species that are parasitic on living plants.

In the SphÆriacei, the substance of the stroma (when present) and of the perithecia is variable, being between fleshy and waxy in Nectriei, and tough, horny, sometimes brittle, in Hypoxylon. A perithecium, or cell excavated in the stroma which fulfils the functions of a perithecium, is always present. The hymenium lines the inner walls of the perithecium, and forms a gelatinous nucleus, consisting of asci and paraphyses. When fully mature, the asci are ruptured and the sporidia escape by a pore which occupies the apex of the perithecium. Sometimes the perithecia are solitary or scattered, and sometimes gregarious, whilst in other instances they are closely aggregated and immersed in a stroma of variable size and form. Conidia, spermatia, pycnidia, &c., have been traced to and associated with some species, but the history of others is still obscure. Many of the coniomycetous forms grouped under the SphÆronemei are probably conditions of the SphÆriacei, as are also the Melanconiei, and some of the Hyphomycetes. A very common fungus, for instance, which is abundant on sticks and twigs, forming rosy or reddish pustules the size of a millet seed, formerly named Tubercularia vulgaris, is known to be the conidia-bearing stroma of the sphÆriaceous fungus, Nectria cinnabarina;[T] and so with many others. The following are the technical characters of the family:—

Fruit consisting of sporidia, mostly definite, contained in asci, springing from a naked or enclosed stratum of fructifying cells and forming a hymenium or nucleus = Ascomycetes.

If the characters of the different families are borne in mind, there will be but little difficulty in assigning any fungus to the order to which it belongs by means of the foregoing remarks. For more minute information, and for analytical tables of the families, orders, and genera, we must refer the student to some special systematic work, which will present fewer difficulties, if he keeps in mind the distinctive features of the families.[U]

To assist in this we have given on the following page an analytical arrangement of the families and orders, according to the system recognized and adopted in the present volume. It is, in all essential particulars, the method adopted in our “Handbook,” based on that of Berkeley’s “Introduction” and “Outlines.”

TABULAR ARRANGEMENT OF FAMILIES AND ORDERS.