II.

STRUCTURE.

Without some knowledge of the structure of fungi, it is scarcely possible to comprehend the principles of classification, or to appreciate the curious phenomena of polymorphism. Yet there is so great a variety in the structure of the different groups, that this subject cannot be compressed within a few paragraphs, neither do we think that this would be desired if practicable, seeing that the anatomy and physiology of plants is, in itself, sufficiently important and interesting to warrant a rather extended and explicit survey. In order to impart as much practical utility as possible to this chapter, it seems advisable to treat some of the most important and typical orders and suborders separately, giving prominence to the features which are chiefly characteristic of those sections, following the order of systematists as much as possible, whilst endeavouring to render each section independent to a considerable extent, and complete in itself. Some groups naturally present more noteworthy features than others, and will consequently seem to receive more than their proportional share of attention, but this seeming inequality could scarcely have been avoided, inasmuch as hitherto some groups have been more closely investigated than others, are more intimately associated with other questions, or are more readily and satisfactorily examined under different aspects of their life-history.

[Illustration: FIG. 1.--Agaric in Process of Growth.]

AGARICINI.--For the structure that prevails in the order to which the mushroom belongs, an examination of that species will be almost sufficient. Here we shall at once recognize three distinct parts requiring elucidation, viz. the rooting slender fibres that traverse the soil, and termed the _mycelium_, or spawn, the stem and cap or pileus, which together constitute what is called the _hymenophore_, and the plates or gills on the under surface of the cap, which bear the _hymenium_. The earliest condition in which the mushroom can be recognized as a vegetable entity is in that of the "spawn" or mycelium, which is essentially an agglomeration of vegetating spores. Its normal form is that of branched, slender, entangled, anastomosing, hyaline threads. At certain privileged points of the mycelium, the threads seem to be aggregated, and become centres of vertical extension. At first only a small nearly globose budding, like a grain of mustard seed, is visible, but this afterwards increases rapidly, and other similar buddings or swellings appear at the base.[A] These are the young hymenophore. As it pushes through the soil, it gradually loses its globose form, becomes more or less elongated, and in this condition a longitudinal section shows the position of the future gills in a pair of opposite crescent-shaped darker-coloured spots near the apex. The dermal membrane, or outer skin, seems to be continuous over the stem and the globose head. At present, there is no external evidence of an expanded pileus and gills; a longitudinal section at this stage shows that the gills are being developed, that the pileus is assuming its cap-like form, that the membrane stretching from the stem to the edge of the young pileus is separating from the edge of the gills, and forming a _veil_, which, in course of time, will separate below and leave the gills exposed. When, therefore, the mushroom has arrived almost at maturity, the pileus expands, and in this act the veil is torn away from the margin of the cap, and remains for a time like a collar around the stem. Fragments of the veil often remain attached to the margin of the pileus, and the collar adherent to the stem falls back, and thenceforth is known as the _annulus_ or ring. We have in this stage the fully-developed hymenophore,--the stem with its ring, supporting an expanded cap or pileus, with gills on the under surface bearing the hymenium.[B] A longitudinal section cut through the pileus and down the stem, gives the best notion of the arrangement of the parts, and their relation to the whole. By this means it will be seen that the pileus is continuous with the stem, that the substance of the pileus descends into the gills, and that relatively the substance of the stem is more fibrous than that of the pileus. In the common mushroom the ring is very distinct surrounding the stem, a little above the middle, like a collar. In some Agarics the ring is very fugacious, or absent altogether. The form of the gills, their mode of attachment to the stem, their colour, and more especially the colour of the spores, are all very important features to be attended to in the discrimination of species, since they vary in different species. The whole substance of the Agaric is cellular. A longitudinal slice from the stem will exhibit under the microscope delicate tubular cells, the general direction of which is lengthwise, with lateral branches, the whole interlacing so intimately that it is difficult to trace any individual thread very far in its course. It will be evident that the structure is less compact as it approaches the centre of the stem, which in many species is hollow. The _hymenium_ is the spore-bearing surface, which is exposed or naked, and spread over the gills. These plates are covered on all sides with a delicate membrane, upon which the reproductive organs are developed. If it were possible to remove this membrane in one entire piece and spread it out flat, it would cover an immense surface, as compared with the size of the pileus, for it is plaited or folded like a lady's fan over the whole of the gill-plates, or lamellæ, of the fungus.[C] If the stem of a mushroom be cut off close to the gills, and the cap laid upon a sheet of paper, with the gills downwards, and left there for a few hours, when removed a number of dark radiating lines will be deposited upon the paper, each line corresponding with the interstices between one pair of gills. These lines are made up of spores which have fallen from the hymenium, and, if placed under the microscope, their character will at once be made evident. If a fragment of the hymenium be also submitted to a similar examination, it will be found that the whole surface is studded with spores. The first peculiarity which will be observed is, that these spores are almost uniformly in groups of four together. The next feature to be observed is, that each spore is borne upon a slender stalk or sterigma, and that four of these sterigmata proceed from the apex of a thicker projection, from the hymenium, called a _basidium_, each basidium being the supporter of four sterigmata, and each sterigma of a spore.[D] A closer examination of the hymenium will reveal the fact that the basidia are accompanied by other bodies, often larger, but without sterigmata or spores; these have been termed _cystidia_, and their structure and functions have been the subject of much controversy.[E] Both kinds of bodies are produced on the hymenium of most, if not all, the Agaricini.

[Illustration: FIG. 2.--Section of Common Mushroom.]

[Illustration: FIG. 3.--_a._ Sterile cells. _b._ Basidia. _c._ Cystidium. From _Gomphidius_ (de Seynes).]

The basidia are usually expanded upwards, so as to have more or less of a clavate form, surmounted by four slender points, or tubular processes, each supporting a spore; the contents of these cells are granular, mixed apparently with oleaginous particles, which communicate through the slender tubes of the spicules with the interior of the spores. Corda states that, although only one spore is produced at a time on each sporophore, when this falls away others are produced in succession for a limited period. As the spores approach maturity, the connection between their contents and the contents of the basidia diminishes and ultimately ceases. When the basidium which bears mature spores is still well charged with granular matter, it may be presumed that the production of a second or third series of spores is quite possible. Basidia exhausted entirely of their contents, and which have become quite hyaline, may often be observed.

The cystidia are usually larger than the basidia, varying in size and form in different species. They present the appearance of large sterile cells, attenuated upwards, sometimes into a slender neck. Corda was of opinion that these were male organs, and gave them the name of _pollinaires_. Hoffmann has also described[F] both these organs under the names of _pollinaria_ and _spermatia_, but does not appear to recognize in them the sexual elements which those names would indicate; whilst de Seynes suggests that the cystidia are only organs returned to vegetative functions by a sort of hypertrophy of the basidia.[G] This view seems to be supported by the fact that, in the section _Pluteus_ and some others, the cystidia are surmounted by short horns resembling sterigmata. Hoffmann has also indicated[H] the passage of cystidia into basidia. The evidence seems to be in favour of regarding the cystidia as barren conditions of basidia. There are to be found upon the hymenium of Agarics a third kind of elongated cells, called by Corda[I] basilary cells, and by Hoffmann "sterile cells," which are either equal in size or smaller than the basidia, with which also their structure agrees, excepting in the development of spicules. These are the "proper cells of the hymenium" of Léveillé, and are simply the terminal cells of the gill structure--cells which, under vigorous conditions, might be developed into basidia, but which are commonly arrested in their development. As suggested by de Seynes, the hymenium seems to be reduced to great simplicity, "one sole and self-same organ is the basis of it; according as it experiences an arrest of development, as it grows and fructifies, or as it becomes hypertrophied, it gives us a paraphyse, a basidium, or a cystidium--in other terms, atrophied basidium, normal basidium and hypertrophied basidium; these are the three elements which form the hymenium."[J]

The only reproductive organs hitherto demonstrated in Agarics are the spores, or, as sometimes called, from their method of production, _basidiospores_.[K] These are at first colourless, but afterwards acquire the colour peculiar to the species. In size and form they are, within certain limits, exceedingly variable, although form and size are tolerably constant in the same species. At first all are globose; as they mature, the majority are ovoid or elliptic; some are fusiform, with regularly attenuated extremities. In _Hygrophorus_ they are rather irregular, reniform, or compressed in the middle. Sometimes the external surface is rough with more or less projecting warts. Some mycologists are of opinion that the covering of the spore is double, consisting of an _exospore_ and an _endospore_, the latter being very fine and delicate. In other orders the double coating of the spore has been demonstrated. When the spore is coloured, the external membrane alone appears to possess colour, the endospore being constantly hyaline. It may be added here, that in this order the spore is simple and unicellular. In _Lactarius_ and _Russula_ the trama, or inner substance, is vesicular. True latex vessels occur occasionally in _Agaricus_, though not filled with milk as in _Lactarius_.

[Illustration: FIG. 4.--_Polyporus giganteus_ (reduced).]

POLYPOREI.--In this order the gill plates are replaced by tubes or pores, the interior of which is lined by the hymenium; indications of this structure having already been exhibited in some of the lower _Agaricini._ In many cases the stem is suppressed. The substance is fleshy in _Boletus_, but in _Polyporus_ the greater number of species are leathery or corky, and more persistent. The basidia, spicules, and quaternate spores agree with those of _Agaricini_.[L] In fact there are no features of importance which relate to the hymenium in any order of _Hymenomycetes_ (the _Tremellini_ excepted) differing from the same organ in _Agaricini_, unless it be the absence of _cystidia_.

[Illustration: FIG. 5.--_Hydnum repandum._]

HYDNEI.--Instead of pores, in this order the hymenium is spread over the surface of spines, prickles, or warts.[M]

AURICULARINI.--The hymenium is more or less even, and in--

CLAVARIEI the whole fungus is club-shaped, or more or less intricately branched, with the hymenium covering the outer surface.

[Illustration: FIG. 6.--_Calocera viscosa._]

[Illustration: FIG. 7.--_Tremella mesenterica._]

TREMELLINI.--In this order we have a great departure from the character of the substance, external appearance, and internal structure of the other orders in this family. Here we have a gelatinous substance, and the form is lobed, folded, convolute, often resembling the brain of some animal. The internal structure has been specially illustrated by M. Tulasne,[N] through the common species, _Tremella mesenterica_. This latter is of a fine golden yellow colour, and rather large size. It is uniformly composed throughout of a colourless mucilage, with no appreciable texture, in which are distributed very fine, diversely branched and anastomosing filaments. Towards the surface, the ultimate branches of this filamentous network give birth, both at their summits and laterally, to globular cells, which acquire a comparatively large size. These cells are filled with a protoplasm, to which the plant owes its orange colour. When they have attained their normal dimensions, they elongate at the summit into two, three, or four distinct, thick, obtuse tubes, into which the protoplasm gradually passes. The development of these tubes is unequal and not simultaneous, so that one will often attain its full dimensions, equal, perhaps, to three or four times the diameter of the generative cell, whilst the others are only just appearing. By degrees, as each tube attains its full size, it is attenuated into a fine point, the extremity of which swells into a spheroidal cell, which ultimately becomes a spore. Sometimes these tubes, or spicules, send out one or two lateral branches, each terminated by a spore. These spores (about ·006 to ·008 _mm._ diameter) are smooth, and deposit themselves, like a fine white dust, on the surface of the _Tremella_ and on its matrix. M. Léveillé[O] was of opinion that the basidia of the Tremellini were monosporous, whilst M. Tulasne has demonstrated that they are habitually tetrasporous, as in other of the Hymenomycetes. Although agreeing in this, they differ in other features, especially in the globose form of the basidia, mode of production of the spicules, and, finally, the division of the basidia into two, three, or four cells by septa which cut each other in their axis. This division precedes the growth of the spicules. It is not rare to see these cells, formed at the expense of an unilocular basidium, become partly isolated from each other; in certain cases they seem to have separated very early, they then become larger than usual, and are grouped on the same filament so as to represent a kind of buds. This phenomenon usually takes place below the level of the fertile cells, at a certain depth in the mucous tissue of the _Tremella_.

Besides the reproductive system here described, Tulasne also made known the existence of a series of filaments which produce spermatia. These filaments are often scattered and confused with those which produce the basidia, and not distinguishable from them in size or any other apparent characteristic, except the manner in which their extremities are branched in order to produce the spermatia. At other times the spermatia-bearing surface covers exclusively certain portions of the fungus, especially the inferior lobes, imparting thereto a very bright orange colour, which is communicated by the layer of spermatia, unmixed with spores. These spots retain their bright colour, while the remainder of the plant becomes pale, or covered with a white dust. The spermatia are very small, spherical, and smooth, scarcely equalling ·002 _mm._ They are sessile, sometimes solitary, sometimes three or four together, on the slightly swollen extremities of certain filaments of the weft of the fungus.[P] Tulasne found it impossible to make these corpuscles germinate, and in all essential particulars they agreed with the spermatia found in ascomycetous fungi.

In the genus _Dacrymyces_, the same observer found the structure to have great affinity with that of _Tremella_. The spores in the species examined were of a different form, being oblong, very obtuse, slightly curved (·013 - ·019 × ·004 - ·006 _mm._), at first unilocular, but afterwards triseptate. The basidia are cylindrical or clavate, filled with coloured granular matter; each of these bifurcates at the summit, and gradually elongates into two very open branches, which are attenuated above, and ultimately each is crowned by a spore. There are to be found also in the species of this genus globose bodies, designated "sporidioles" by M. Léveillé, which Tulasne took considerable care to trace to their source. He thus accounts for them:--Each of the cells of the spore emits exteriorly one or several of these corpuscles, supported on very short and very slender pedicels, which remain after the corpuscles are detached from them, new corpuscles succeeding the first as long as there remains any plastic matter within the spore. The pedicels are not all on the same plane; they are often implanted all on the same, and oftenest on the convex side of the reproductive body. These corpuscles, though placed under the most favourable conditions, never gave the least sign of vegetation, and Tulasne concludes that they are spermatia, analogous to those produced in _Tremella_. The spores which produce spermatia are not at all apt to germinate, whilst those which did not produce spermatia germinated freely. Hence it would appear that, although all spores seem to be perfectly identical, they have not all the same function. The same observer detected also amongst specimens of the _Dacrymyces_ some of a darker and reddish tint, always bare of spores or spermatia on the surface, and these presented a somewhat different structure. Where the tissue had turned red it was sterile, the constituent filaments, ordinarily colourless, and almost empty of solid matter, were filled with a highly-coloured protoplasm; they were of less tenuity, more irregularly thick, and instead of only rarely presenting partitions, and remaining continuous, as in other parts of the plant, were parcelled out into an infinity of straight or curved pieces, angular and of irregular form, especially towards the surface of the fungus, where they compose a sort of pulp, varying in cohesion according to the dry or moist condition of the atmosphere. All parts of these reddish individuals seemed more or less infected with this disintegration, the basidia divided by transverse diaphragms into several cylindrical or oblong pieces, which finally become free. Transitional conditions were also observed in mixed individuals. This sterile condition is called by Tulasne "gemmiparous," and he believes that it has ere now given origin to one or more spurious species, and misled mycologists as to the real structure of perfect and fruitful _Dacrymyces_.

PHALLOIDEI.--In this order the hymenium is at first enclosed within a sort of peridium or universal volva, maintaining a somewhat globose or egg-shape. This envelope consists of an outer and inner coat of somewhat similar texture, and an intermediate gelatinous layer, often of considerable thickness. When a section is made of the fungus, whilst still enclosed in the volva, the hymenium is found to present numerous cavities, in which basidia are developed, each surmounted by spicules (four to six) bearing oval or oblong spores.[Q] It is very difficult to observe the structure of the hymenium in this order, on account of its deliquescent nature. As the hymenium approaches maturity, the volva is ruptured, and the plant rapidly enlarges. In _Phallus_, a long erect cellular stem bears the cap, over which the hymenium is spread, and this expands enormously after escaping the restraint of the volva. Soon after exposure, the hymenium deliquesces into a dark mucilage, coloured by the minute spores, which drips from the pileus, often diffusing a most loathsome odour for a considerable distance. In _Clathrus_, the receptacle forms a kind of network. In _Aseröe_, the pileus is beautifully stellate. In many the attractive forms would be considered objects of beauty, were it not for their deliquescence, and often foetid odour.[R]

[Illustration: FIG. 8.--Basidia and spores of _Phallus_.]

PODAXINEI.--This is a small but very curious group of fungi, in which the peridium resembles a volva, which is more or less confluent with the surface of the pileus. They assume hymenomycetal forms, some of them looking like Agarics, Boleti, or species of _Hydnum_, with deformed gills, pores, or spines; in _Montagnites_, in fact, the gill structure is very distinct. The spores are borne in definite clusters on short pedicels in such of the genera as have been examined.[S]

HYPOGÆI.--These are subterranean puff-balls, in which sometimes a distinct peridium is present; but in most cases it consists entirely of an external series of cells, continuous with the internal structure, and cannot be correctly estimated as a peridium. The hymenium is sinuous and convolute, bearing basidia with sterigmata and spores in the cavities. Sometimes the cavities are traversed by threads, as in the _Myxogastres_. The spores are in many instances beautifully echinulate, sometimes globose, at others elongated, and produced in such numbers as to lead to the belief that their development is successive on the spicules. When fully matured, the peridia are filled with a dusty mass of spores, so that it is scarcely possible in this condition to gain any notion of the structure. This is, indeed, the case with nearly all _Gasteromycetes_. The hypogæous fungi are curiously connected with _Phalloidei_ by the genus _Hysterangium_.

[Illustration: FIG. 9.--Basidia and spores of _Lycoperdon_.]

TRICHOGASTRES.[T]--In their early stages the species contained in this group are not gelatinous, as in the _Myxogastres_, but are rather fleshy and firm. Very little has been added to our knowledge of structure in this group since 1839 and 1842, when one of us wrote to the following effect:--If a young plant of _Lycoperdon coelatum_ or _L. gemmatum_ be cut through and examined with a common pocket lens, it will be found to consist of a fleshy mass, perforated in every direction with minute elongated, reticulated, anastomosing, labyrinthiform cavities. The resemblance of these to the tubes of _Boleti_ in an early stage of growth, first led me to suspect that there must be some very close connection between them. If a very thin slice now be taken, while the mass is yet firm, and before there is the slightest indication of a change of colour, the outer stratum of the walls of these cavities is found to consist of pellucid obtuse cells, placed parallel to each other like the pile of velvet, exactly as in the young hymenium of an Agaric or Boletus. Occasionally one or two filaments cross from one wall to another, and once I have seen these anastomose. At a more advanced stage of growth, four little spicules are developed at the tips of the sporophores, all of which, as far as I have been able to observe, are fertile and of equal height, and on each of these spicules a globose spore is seated. It is clear that we have here a structure identical with that of the true Hymenomycetes, a circumstance which accords well with the fleshy habit and mode of growth. There is some difficulty in ascertaining the exact structure of the species just noticed, as the fruit-bearing cells, or sporophores, are very small, and when the spicules are developed the substance becomes so flaccid that it is difficult to cut a proper slice, even with the sharpest lancet. I have, however, satisfied myself as to the true structure by repeated observations. But should any difficulty arise in verifying it in the species in question, there will be none in doing so in _Lycoperdon giganteum_. In this species the fructifying mass consists of the same sinuous cavities, which are, however, smaller, so that the substance is more compact, and I have not seen them traversed by any filaments. In an early stage of growth, the surface of the hymenium, that is of the walls of the cavities, consists of short threads composed of two or three articulations, which are slightly constricted at the joints, from which, especially from the last, spring short branchlets, often consisting of a single cell. Sometimes two or more branchlets spring from the same point. Occasionally the threads are constricted without any dissepiments, the terminal articulations are obtuse, and soon swell very much, so as greatly to exceed in diameter those on which they are seated. When arrived at their full growth, they are somewhat obovate, and produce four spicules, which at length are surmounted each with a globose spore. When the spores are fully developed, the sporophores wither, and if a solution of iodine be applied, which changes the spores to a rich brown, they will be seen still adhering by their spicules to the faded sporophores. The spores soon become free, but the spicule often still adheres to them; but they are not attached to the intermingled filaments. In _Bovista plumbea_, the spores have very long peduncles.[U] As in the _Hymenomycetes_, the prevailing type of reproductive organs consisted of quaternary spores borne on spicules; so in _Gasteromycetes_, the prevailing type, in so far as it is yet known, is very similar, in some cases nearly identical, consisting of a definite number of minute spores borne on spicules seated on basidia. In a very large number of genera, the minute structure and development of the fructification (beyond the mature spores) is almost unknown, but from analogy it may be concluded that a method prevails in a large group like the _Myxogastres_ which does not differ in essential particulars from that which is known to exist in other groups. The difficulties in the way of studying the development of the spores in this are far greater than in the previous order.

[Illustration: FIG. 10.--_a._ Threads of _Trichia_. _b._ Portion further magnified, with spores. _c._ Portion of spinulose thread.]

MYXOGASTRES.--At one time that celebrated mycologist, Professor De Bary, seemed disposed to exclude this group from the vegetable kingdom altogether, and relegate them to a companionship with amoeboid forms. But in more recent works he seems to have reconsidered, and almost, if not entirely, abandoned, that disposition. These fungi, mostly minute, are characterized in their early stages by their gelatinous nature. The substance of which they are then composed bears considerable resemblance to sarcode, and, did they never change from this, there might be some excuse for doubting as to their vegetable nature; but as the species proceed towards maturity they lose their mucilaginous texture, and become a mass of spores, intermixed with threads, surrounded by a cellular peridium. Take, for instance, the genus _Trichia_, and we have in the matured specimens a somewhat globose peridium, not larger than a mustard seed, and sometimes nearly of the same colour; this ultimately ruptures and exposes a mass of minute yellow spherical spores, intermixed with threads of the same colour.[V] These threads, when highly magnified, exhibit in themselves a spiral arrangement, which has been the basis of some controversy, and in some species these threads are externally spinulose. The chief controversy on these threads has been whether the spiral markings are external or internal, whether caused by twisting of the thread or by the presence of an external or internal fibre. The spiral appearance has never been called in question, only the structure from whence it arises, and this, like the striæ of diatoms, is very much an open question. Mr. Currey held that the spiral appearance may be accounted for by supposing the existence of an accurate elevation in the wall of the cell, following a spiral direction from one end of the thread to the other. This supposition would, he thinks, accord well with the optical appearances, and it would account exactly for the undulations of outline to which he alludes. He states that he had in his possession a thread of _Trichia chrysosperma_, in which the spiral appearance was so manifestly caused by an elevation of this nature, in which it is so clear that no internal spiral fibre exists, that he did not think there could be a doubt in the mind of any person carefully examining it with a power of 500 diameters that the cause of the spiral appearance was not a spiral fibre. In _Arcyria_, threads of a different kind are present; they mostly branch and anastomose, and are externally furnished with prominent warts or spines, which Mr. Currey[W] holds are also arranged in a spiral manner around the threads. In other Myxogastres, threads are also present without any appreciable spiral markings or spines. In the mature condition of these fungi, they so clearly resemble, and have such close affinities with, the Trichogastres that one is led almost to doubt whether it was not on hasty grounds, without due examination or consideration, that proposals were made to remove them from the society of their kindred.

[Illustration: FIG. 11.--_Arcyria incarnata_, with portion of threads and spore, magnified.]

Very little is known of the development of the spores in this group; in the early stages the whole substance is so pulpy, and in the latter so dusty, whilst the transition from one to the other is so rapid, that the relation between the spores and threads, and their mode of attachment, has never been definitely made out. It has been supposed that the spinulose projections from the capillitium in some species are the remains of pedicels from which, the spores have fallen, but there is no evidence beyond this supposition in its favour, whilst on the other hand, in _Stemonitis_, for instance, there is a profuse interlacing capillitium, and no spines have been detected. In order to strengthen the supposition, spines should be more commonly present. The threads, or capillitium, form a beautiful reticulated network in _Stemonitis_, _Cribraria_, _Diachæa_, _Dictydium_, &c. In _Spumaria_, _Reticularia_, _Lycogala_, &c., they are almost obsolete.[X] In no group is the examination of the development of structure more difficult, for the reasons already alleged, than in the Myxogastres.

[Illustration: FIG. 12.--_Diachæa elegans._]

[Illustration: FIG. 13.--_Cyathus vernicosus._]

NIDULARIACEI.--This small group departs in some important particulars from the general type of structure present in the rest of the Gasteromycetes.[Y] The plants here included may be described under three parts, the mycelium, the peridium, and the sporangia. The mycelium is often plentiful, stout, rigid, interlacing, and coloured, running over the surface of the soil, or amongst the vegetable débris on which the fungi establish themselves. The peridia are seated upon this mycelium, and in most instances are at length open above, taking the form of cups, or beakers. These organs consist of three strata of tissue varying in structure, the external being fibrous, and sometimes hairy, the interior cellular and delicate, the intermediate thick and at length tough, coriaceous, and resistant. When first formed, the peridia are spherical, they then elongate and expand, the mouth being for some time closed by a veil, or diaphragm, which ultimately disappears. Within the cups lentil-shaped bodies are attached to the base and sides by elastic cords. These are the sporangia. Each of these has a complicated structure; externally there is a filamentous tunic, composed of interlaced fibres, sometimes called the peridiole; beneath this is the cortex, of compact homogenous structure, then follows a cellular thicker stratum, bearing, towards the centre of the sporangia, delicate branched threads, or sporophores, on which, at their extremities, the ovate spores are generated, sometimes in pairs, but normally, it would seem that they are quaternary on spicules, the threads being true basidia. The whole structure is exceedingly interesting and peculiar, and may be studied in detail in Tulasne's memoir on this group.

SPHÆRONEMEI.--In this very large and, within certain limits, variable order, there is but little of interest as regards structure, which is not better illustrated elsewhere; as, for instance, some sort of perithecium is always present, but this can be better studied in the _Sphæriacei_. The spores are mostly very minute, borne on delicate sporophores, which originate from the inner surface of the perithecia, but the majority of so-called species are undoubtedly conditions of sphæriaceous fungi, either spermatogonia or pycnidia, and are of much more interest when studied in connection with the higher forms to which they belong.[Z] Probably the number of complete and autonomous species are very few.

[Illustration: FIG. 14.--_Cyathus._ _a._ Sporangium. _b._ Section. _c._ Sporophore. _d._ Spores.]

MELANCONIEI.--Here, again, are associated together a great number of what formerly were considered good species of fungi, but which are now known to be but conditions of other forms. One great point of distinction between these and the preceding is the absence of any true perithecium, the spores being produced in a kind of spurious receptacle, or from a sort of stroma. The spores are, as a rule, larger and much more attractive than in _Sphæronemei_, and, in some instances, are either very fine, or very curious. Under this head we may mention the multiseptate spores of _Coryneum_; the tri-radiate spores of _Asterosporium_; the curious crested spores of _Pestalozzia_; the doubly crested spores of _Dilophospora_; and the scarcely less singular gelatinous coated spores of _Cheirospora_. In all cases the fructification is abundant, and the spores frequently ooze out in tendrils, or form a black mass above the spurious receptacle from which they issue.[a]

[Illustration: FIG. 15.--_Asterosporium Hoffmanni._]

TORULACEI.--In this order there seems at first to be a considerable resemblance to the _Dematiei_, except that the threads are almost obsolete, and the plant is reduced to chains of spores, without trace of perithecium, investing cuticle, or definite stroma. Sometimes the spores are simple, in other cases septate, and in _Sporochisma_ are at first produced in an investing cell. In most cases simple threads at length become septate, and are ultimately differentiated into spores, which separate at the joints when fully mature.

[Illustration: FIG. 16.--Barren Cysts and Pseudospores of _Lecythea_.]

[Illustration: FIG. 17.--_Coleosporium Tussilaginis_, Lev.]

[Illustration: FIG. 18.--_Melampsora salicina._]

CÆOMACEI.--Of far greater interest are the Coniomycetous parasites on living plants. The present order includes those in which the spore[b] is reduced to a single cell; and here we may observe that, although many of them are now proved to be imperfect in themselves, and only forms or conditions of other fungals, we shall write of them here without regard to their duality. These originate, for the most part, within the tissues of living plants, and are developed outwards in pustules, which burst through the cuticle. The mycelium penetrates the intercellular passages, and may sometimes be found in parts of the plants where the fungus does not develop itself. There is no proper excipulum or peridium, and the spores spring direct from a more compacted portion of the mycelium, or from a cushion-like stroma of small cells. In _Lecythea_, the sub-globose spores are at first generated at the tips of short pedicels, from which they are ultimately separated; surrounding these spores arise a series of barren cells, or cysts, which are considerably larger the true spores, and colourless, while the spores are of some shade of yellow or orange.[c] In _Trichobasis_, the spores are of a similar character, sub-globose, and at first pedicellate; but there are no surrounding cysts, and the colour is more usually brown, although sometimes yellow. In _Uredo_, the spores are at first generated singly, within a mother cell; they are globose, and either yellow or brown, without any pedicel. In _Coleosporium_, there are two kinds of spores, those of a pulverulent nature, globose, which are sometimes produced alone at the commencement of the season, and others which originate as an elongated cell; this becomes septate, and ultimately separates at the joints. During the greater part of the year, both kinds of spores are to be found in the same pustule. In _Melampsora_, the winter spores are elongated and wedge-shaped, compacted together closely, and are only matured during winter on dead leaves; the summer spores are pulverulent and globose, being, in fact, what were until recently regarded as species of _Lecythea_. In _Cystopus_, the spores are sub-globose, or somewhat angular, generated in a moniliform manner, and afterwards separating at the joints. The upper spore is always the oldest, continuous production of spores going on for some time at the base of the chain. Under favourable conditions of moisture, each of these spores, or conidia, as De Bary terms them, is capable of producing within itself a number of zoospores;[d] these ultimately burst the vesicle, move about by the aid of vibratile cilia, and at last settle down to germinate. Besides these, other reproductive bodies are generated upon the mycelium, within the tissues of the plant, in the form of globose oogonia, or resting spores, which, when mature, also enclose great numbers of zoospores. Similar oogonia are produced amongst the _Mucedines_ in the genus _Peronospora_, to which De Bary considers _Cystopus_ to be closely allied. At all events, this is a peculiarity of structure and development not as yet met with in any other of the _Cæomacei_. In _Uromyces_ is the nearest approach to the _Pucciniæi_; in fact, it is _Puccinia_ reduced to a single cell. The form of spore is usually more angular and irregular than in _Trichobasis_, and the pedicel is permanent. It may be remarked here, that of the foregoing genera, many of the species are not autonomous that have hitherto been included amongst them. This is especially true of _Lecythea_, _Trichobasis_, and, as it now appears, of _Uromyces_.[e]

[Illustration: FIG. 19.--_Cystopus candidus._]

[Illustration: FIG. 20.--_Xenodochus carbonarius._]

[Illustration: FIG. 21.--_Phragmidium bulbosum._]

PUCCINIÆI.--This group differs from the foregoing chiefly in having septate spores. The pustules, or sori, break through the cuticle in a similar manner, and here also no true peridium is present. In _Xenodochus_, the highest development of joints is reached, each spore being composed of an indefinite number, from ten to twenty cells. With it is associated an unicellular yellow Uredine, of which it is a condition. Probably, in every species of the _Pucciniæi_, it may hereafter be proved, as it is now suspected, that an unicellular Uredine precedes or is associated with it, forming a condition, or secondary form of fruit of that species. Many instances of that kind have already been traced by De Bary,[f] Tulasne, and others, and some have been a little too rashly surmised by their followers. In _Phragmidium_, the pedicel is much more elongated than in _Xenodochus_, and the spore is shorter, with fewer and a more definite number of cells for each species; Mr. Currey is of opinion that each cell of the spore in _Phragmidium_ has an inner globose cell, which he caused to escape by rupture of the outer cell wall as a sphæroid nucleus,[g] leading to the inference that each cell has its own individual power of germination and reproduction. In _Triphragmium_, there are three cells for each spore, two being placed side by side, and one superimposed. In one species, however, _Triphragmium deglubens_ (North American), the cells are arranged as in _Phragmidium_, so that this represents really a tricellular _Phragmidium_, linking the present with the latter genus. In _Puccinia_ the number of species is by far the most numerous; in this genus the spores are uniseptate, and, as in all the _Pucciniæi_, the peduncles are permanent. There is great variability in the compactness of the spores in the sori, or pulvinules. In some species, the sori are so pulverulent that the spores are as readily dispersed as in the Uredines, in others they are so compact as to be separated from each other with great difficulty. As might be anticipated, this has considerable effect on the contour of the spores, which in pulverulent species are shorter, broader, and more ovate than in the compact species. If a section of one of the more compact sori be made, it will be seen that the majority of the spores are side by side, nearly at the same level, their apices forming the external surface of the sori, but it will not be unusual to observe smaller and younger spores pushing up from the hymenial cells, between the peduncles of the elder spores, leading to the inference that there is a succession of spores produced in the same pulvinule. In _Podisoma_, a rather anomalous genus, the septate spores are immersed in a gelatinous stratum, and some authors have imagined that they have an affinity with the Tremellini, but this affinity is more apparent than real. The phenomena of germination, and their relations to _Roestelia_, if substantiated, establish their claim to a position amongst the _Pucciniæi_.[h] It seems to us that _Gymnosporangium_ does not differ generically from _Podisoma_. In a recently-characterized species, _Podisoma Ellisii_, the spores are bi-triseptate. This is, moreover, peculiar from the great deficiency in the gelatinous element. In another North American species, called _Gymnosporangium biseptatum_, Ellis, which is distinctly gelatinous, there are similar biseptate spores, but they are considerably broader and more obtuse. In other described species they are uniseptate.

[Illustration: FIG. 22.--Pseudospores of _Puccinia_.]

USTILAGINEI.--These fungi are now usually treated as distinct from the _Cæomacei_, to which they are closely related.[i] They are also parasitic on growing plants, but the spores are usually black or sooty, and never yellow or orange; on an average much smaller than in the _Cæomacei_. In _Tilletia_, the spores are spherical and reticulated, mixed with delicate threads, from whence they spring. In the best known species, _Tilletia caries_, they constitute the "bunt" of wheat. The peculiarities of germination will be alluded to hereafter. In _Ustilago_, the minute sooty spores are developed either on delicate threads or in compacted cells, arising first from a sort of semi-gelatinous, grumous stroma. It is very difficult to detect any threads associated with the spores. The species attack the flowers and anthers of composite and polygonaceous plants, the leaves, culms, and germen of grasses, &c., and are popularly known as "smuts." In _Urocystis_ and _Thecaphora_, the spores are united together into sub-globose bodies, forming a kind of compound spore. In some species of _Urocystis_, the union which subsists between them is comparatively slight. In _Thecaphora_, on the contrary, the complex spore, or agglomeration of spores, is compact, being at first apparently enclosed in a delicate cyst. In _Tuburcinia_, the minute cells are compacted into a hollow sphere, having lacunæ communicating with the interior, and often exhibiting the remains of a pedicel.

[Illustration: FIG. 23.--_Thecaphora hyalina._]

[Illustration: FIG. 24.--_Æcidium Berberidis._]

ÆCIDIACEI.--This group differs from the foregoing three groups prominently in the presence of a cellular peridium, which encloses the spores; hence some mycologists have not hesitated to propose their association with the Gasteromycetes, although every other feature in their structure seems to indicate a close affinity with the _Cæomacei_. The pretty cups in the genus _Æcidium_ are sometimes scattered and sometimes collected in clusters, either with spermogonia in the centre or on the opposite surface. The cups are usually white, composed of regularly arranged bordered cells at length bursting at the apex, with the margins turned back and split into radiating teeth. The spores are commonly of a bright orange or golden yellow, sometimes white or brownish, and are produced in chains, or moniliform strings, slightly attached to each other,[j] and breaking off at the summit at the same time that they continue to be produced at the base, so that for some time there is a successive production of spores. The spermogonia are not always readily detected, as they are much smaller than the peridia, and sometimes precede them. The spermatia are expelled from the lacerated and fringed apices, and are very minute and colourless. In _Roestelia_ the peridia are large, growing in company, and splitting longitudinally in many cases, or by a lacerated mouth. In most instances, the spores are brownish, but in a splendid species from North America (_Roestelia aurantiaca_, Peck), recently characterized, they are of a bright orange. If Oersted is correct in his observations, which await confirmation, these species are all related to species of _Podisoma_ as a secondary form of fruit.[k] In the _Roestelia_ of the pear-tree, as well as in that of the mountain ash, the spermogonia will be found either in separate tufts on discoloured spots, or associated with the _Roestelia_, In _Peridermium_ there is very little structural difference from _Roestelia_, and the species are all found on coniferous trees. In _Endophyllum_, the peridia are immersed in the succulent substance of the matrix; whilst in _Graphiola_, there is a tougher and withal double peridium, the inner of which forms a tuft of erect threads resembling a small brush.[l]

[Illustration: FIG. 25.--_Helminthosporium molle._]

HYPHOMYCETES.--The predominant feature in the structure of this order has already been intimated to consist in the development of the vegetative system under the form of simple or branched threads, on which the fruit is generated. The common name of mould is applied to them perhaps more generally than to other groups, although the term is too vague, and has been too vaguely applied to be of much service in giving an idea of the characteristics of this order. Leaving the smaller groups, and confining ourselves to the _Dematiei_ and the _Mucedines_, we shall obtain some notion of the prevalent structure. In the former the threads are more or less carbonized, in the latter nearly colourless. One of the largest genera in _Dematiei_ is _Helminthosporium_. It appears on decaying herbaceous plants, and on old wood, forming effused black velvety patches. The mycelium, of coloured jointed threads, overlays and penetrates the matrix; from this arise erect, rigid, and usually jointed threads, of a dark brown, nearly black colour at the base, but paler towards the apex. In most cases these threads have an externally cortical layer, which imparts rigidity; usually from the apex, but sometimes laterally, the spores are produced. Although sometimes colourless, these are most commonly of some shade of brown, more or less elongated, and divided transversely by few or many septa. In _Helminthosporium Smithii_, the spores much exceed the dimensions of the threads;[m] in other species they are smaller. In _Dendryphium_, the threads and spores are very similar, except that the threads are branched at their apex, and the spores are often produced one at the end of another in a short chain.[n] In _Septosporium_ again, the threads and spores are similar, but the spores are pedicellate, and attached at or near the base; whilst in _Acrothecium_, with similar threads and spores, the latter are clustered together at the apex of the threads. In _Triposporium_, the threads are similar, but the spores are tri-radiate; and in _Helicoma_, the spores are twisted spirally. Thus, we might pass through all the genera to illustrate this chief feature of coloured, septate, rather rigid, and mostly erect threads, bearing at some point spores, which in most instances are elongated, coloured, and septate.

[Illustration: FIG. 26.--_Acrothecium simplex._]

[Illustration: FIG. 27.--_Peronospora Arenariæ._]

MUCEDINES.--Here, on the other hand, the threads, if coloured at all, are still delicate, more flexuous, with much thinner walls, and never invested with an external cortical layer. One of the most important and highly developed genera is _Peronospora_, the members of which are parasitic upon and destructive of living vegetables. It is to this genus that the mould of the too famous potato disease belongs. Professor De Bary has done more than any other mycologist in the investigation and elucidation of this genus; and his monograph is a masterpiece in its way.[o] He was, however, preceded by Mr. Berkeley, and more especially by Dr. Montagne, by many years in elucidation of the structure of the flocci and conidia in a number of species.[p] In this genus, there is a delicate mycelium, which penetrates the intercellular passages of living plants, giving rise to erect branched threads, which bear at the tips of their ultimate ramuli, sub-globose, ovate, or elliptic spores, or, as De Bary terms them--conidia. Deeply seated on the mycelium, within the substance of the foster plant, other reproductive bodies, called oogonia, originate. These are spherical, more or less warted and brownish, the contents of which become differentiated into vivacious zoospores, capable, when expelled, of moving in water by the aid of vibratile cilia. A similar structure has already been indicated in _Cystopus_, otherwise it is rare in fungi, if the _Saprolegniei_ be excluded. In _Botrytis_ and in _Polyactis_, the flocci and spores are similar, but the branches of the threads are shorter and more compact, and the septa are more common and numerous; the oogonia also are absent. De Bary has selected _Polyactis cinerea_, as it occurs on dead vine leaves, to illustrate his views of the dualism which he believes himself to have discovered in this species. "It spreads its mycelium in the tissue which is becoming brown," he writes, "and this shows at first essentially the same construction and growth as that of the mycelium filaments of _Aspergillus_." On the mycelium soon appear, besides those which are spread over the tissue of the leaves, strong, thick, mostly fasciculate branches, which stand close to one another, breaking forth from the leaf and rising up perpendicularly, the conidia-bearers. They grow about 1 _mm._ long, divide themselves, by successively rising partitions, into some prominent cylindrical linked cells, and then their growth is ended, and the upper cell produces near its point three to six branches almost standing rectangularly. Of these the under ones are the longest, and they again shoot forth from under their ends one or more still shorter little branches. The nearer they are to the top, the shorter are the branches, and less divided; the upper ones are quite branchless, and their length scarcely exceeds the breadth of the principal stem. Thus a system of branches appears, upon which, on a small scale, a bunch of grapes is represented. All the twigs soon end their growth; they all separate their inner space from the principal stem, by means of a cross partition placed close to it. All the ends, and also that of the principal stem, swell about the same time something like a bladder, and on the upper free half of each swelling appear again, simultaneously, several fine protuberances, close together, which quickly grow to little oval bladders filled with protoplasm, and resting on their bearers with a sub-sessile, pedicellate, narrow basis, and which at length separate themselves through a partition as in _Aspergillus_. The detached cells are the conidia of our fungus; only one is formed on each stalk. When the formation is completed in the whole of the panicle, the little branches which compose it are deprived of their protoplasm in favour of the conidia; it is the same with the under end of the principal stem, the limits of which are marked by a cross partition. The delicate wall of these parts shrinks up until it is unrecognizable; all the conidia of the panicle approach one another to form an irregular grape-like bunch, which rests loosely on the bearer, and from which it easily falls away as dust. If they be brought into water they fall off immediately; only the empty, shrivelled, delicate skins are to be found on the branch which bore them, and the places on which they are fixed to the principal stem clearly appear as round circumscribed hilums, generally rather arched towards the exterior. The development of the main stem is not ended here. It remains solid and filled with protoplasm as far as the portion which forms the end through its conidia. Its end, which is to be found among these pieces, becomes pointed after the ripening of the first panicle, pushes the end of the shrivelled member on one side, and grows to the same length as the height of one or two panicles, and then remains still, to form a second panicle similar to the first. This is later equally perfoliated as the first, then a third follows, and thus a large number of panicles are produced after and over one another on the same stem. In perfect specimens, every perfoliated panicle hangs loosely to its original place on the surface of the stem, until by shaking or the access of water to it, it falls immediately into the single conidia, or the remains of branches, and the already-mentioned oval hilums are left behind. Naturally, the stem becomes longer by every perfoliation; in luxuriant specimens the length can reach that of some lines. Its partition is already, by the ripening of the first panicle from the beginning of its foundation, strong and brown; it is only colourless at the end which is extending, and in all new formations. During all these changes the filament remains either unbranched, except as regards the transient panicles, or it sends out here and there, at the perfoliated spots, especially from the lower ones, one or two strong branches, standing opposite one another and resembling the principal stem.

[Illustration: FIG. 28.--_Polyactis cinerea._ _a._ Apex of hypha.]

The mycelium, which grows so exuberantly in the leaf, often brings forth many other productions, which are called _sclerotia_, and are, according to their nature, a thick bulbous tissue of mycelium filaments. Their formation begins with the profuse ramification of the mycelium threads in some place or other; generally, but not always, in the veins of the leaf; the intertwining twigs form an uninterrupted cavity, in which is often enclosed the shrivelling tissue of the leaf. The whole body swells to a greater thickness than that of the leaf, and protrudes on the surface like a thickened spot. Its form varies from circular to fusiform; its size is also very unequal, ranging between a few lines and about half a millimetre in its largest diameter. At first it is colourless, but afterwards its outer layers of cells become round, of a brown or black colour, and it is surrounded by a black rind, consisting of round cells, which separate it from the neighbouring tissue. The tissue within the rind remains colourless; it is an entangled uninterrupted tissue of fungus filaments, which gradually obtain very solid, hard, cartilaginous coats. The sclerotium, which ripens as the rind becomes black, loosens itself easily from the place of its formation, and remains preserved after the latter is decayed.

[Illustration: FIG. 29.--_Peziza Fuckeliana._ _a._ Natural size. _b._ Section enlarged. _c._ Ascus and sporidia.]

The sclerotia are, here as in many other fungi, biennial organs, designed to begin a new vegetation after a state of apparent quietude, and to send forth special fruit-bearers. They may in this respect be compared to the bulbs and perennial roots of under shrubs. The usual time for the development of the sclerotia is late in the autumn, after the fall of the vine leaves. As long as the frost does not set in, new ones continually spring up, and each one attains to ripeness in a few days. If frost appears, it can lie dry a whole year, without losing its power of development. This latter commences when the sclerotium is brought into contact with damp ground during the usual temperature of our warmer seasons. If this occur soon, at the latest some weeks after it is ripe, new vegetation grows very quickly, generally after a few days; in several parts the colourless filaments of the inner tissue begin to send out clusters of strong branches, which, breaking through the black rind, stretch themselves up perpendicularly towards the surface, separate from one another, and then take all the characteristics of the conidia-bearers. Many such clusters can be produced on one sclerotium, so that soon the greater part of the surface is covered by filamentous conidia-bearers with their panicles. The colourless tissue of the sclerotium disappears in the same degree as the conidia-bearers grow, and at last the black rind remains behind empty and shrivelled. If we bring, after many months, for the first time, the ripe sclerotium, in damp ground, in summer or autumn, after it has ripened, the further development takes place more slowly, and in an essentially different form. It is true that from the inner tissue numerous filamentous branches shoot forth at the cost of this growing fascicle, and break through the black rind, but its filaments remain strongly bound, in an almost parallel situation, to a cylindrical cord, which for a time lengthens itself and spreads out its free end to a flat plate-like disc. This is always formed of strongly united threads, ramifications of the cylindrical cord. On the free upper surface of the disc, the filaments shoot forth innumerable branches, which, growing to the same height, thick and parallel with one another, cover the before-named disc. Some remain narrow and cylindrical, are very numerous, and produce fine hairs (paraphyses); others, also very numerous, take the form of club-like ampulla cells, and each one forms in its interior eight free swimming oval spores. Those ampulla cells are sporidiiferous asci. After the spores have become ripe, the free point of the utricle bursts, and the spores are scattered to a great distance by a mechanism which we will not here further describe. New ampullas push themselves between those which are ripening and withering; a disc can, under favourable circumstances, always form new asci for weeks at a time. The number of the already described utricle-bearers is different, according to the size of the sclerotium; smaller specimens usually produce only one, larger two to four. The size is regulated by that of the sclerotia, and ranges, in full-grown specimens, between one and more millimetres for the length of the stalk, and a half to three (seldom more) millimetres for the breadth of the disc.[q] For some time the conidia form, belonging to the Mucedines, has been known as _Botrytis cinerea_ (or _Polyactis cinerea_). The compact mycelium, or sclerotium, as an imperfect fungus, bore the name of _Sclerotium echinatum_, whilst to the perfect and cup-like form has been given the name of _Peziza Fuckeliana_. We have reproduced De Bary's life-history of this mould here, as an illustration of structure in the _Mucedines_, but hereafter we shall have to write of similar transformations when treating of polymorphism.

The form of the threads, and the form and disposition of the spores, vary according to the genera of which this order is composed. In _Oidium_ the mostly simple threads break up into joints. Many of the former species are now recognized as conditions of _Erysiphe_. In _Aspergillus_, the threads are simple and erect, with a globose head, around which are clustered chains of simple spores. In _Penicillium_, the lower portion of the threads is simple, but they are shortly branched at the apex, the branches being terminated by necklaces of minute spores. In _Dactylium_, the threads are branched, but the spores are collected in clusters usually, and are moreover septate. In other genera similar distinctions prevail. These two groups of black moulds and white moulds are the noblest, and contain the largest number of genera and species amongst the _Hyphomycetes_. There is, however, the small group of _Isariacei_, in which the threads are compacted, and a semblance of such hymenomycetal forms as _Clavaria_ and _Pterula_ is the result, but it is doubtful if this group contains many autonomous species. In another small group, the _Stilbacei_, there is a composite character in the head, or receptacle,[r] and in the stem when the latter is present. Many of these, again, as _Tubercularia_, _Volutella_, _Fusarium_, &c., contain doubtful species. In _Sepedoniei_ and _Trichodermacei_, the threads are reduced to a minimum, and the spores are such a distinctive element that through these groups the _Hyphomycetes_ are linked with the _Coniomycetes_. These groups, however, are not of sufficient size or importance to demand from us, in a work of this character, anything more than the passing allusion which we have given to them.

[Illustration: FIG. 30.--_Penicillium chartarum_, Cooke.]

We come now to consider the structure in the Sporidiifera, in which the fructifying corpuscles or germs, whether called spores or sporidia, are generated within certain privileged cysts, usually in definite numbers. In systematic works, these are included under two orders, the _Physomycetes_ and the _Ascomycetes_. The former of these consists of cyst-bearing moulds, and from their nearest affinity to the foregoing will occupy the first place.

[Illustration: FIG. 31.--_Mucor mucedo_, with three sporangia. _a._ Portion of frill with sporangiola.]

PHYSOMYCETES include, especially amongst the _Mucorini_, many most interesting and instructive species for study, which even very lately have occupied the attention of continental mycologists. Most of these phenomena are associated more or less with reproduction, and as such will have to be adverted to again, but there are points in the structure which can best be alluded to here. Again taking Professor de Bary's researches as our guide,[s] we will illustrate this by the common _Mucor mucedo_: If we bring quite fresh horse-dung into a damp confined atmosphere, for example, under a bell-glass, there appears on its surface, after a few days, an immense white mildew. Upright strong filaments of the breadth of a hair raise themselves over the surface, each of them soon shows at its point a round little head, which gradually becomes black, and a closer examination shows us that in all principal points it perfectly agrees with the sporangia of other species. Each of these white filaments is a sporangia-bearer. They spring from a mycelium which is spread in the dung, and appear singly upon it. Certain peculiarities in the form of the sporangium, and the little long cylindrical spores, which, when examined separately, are quite flat and colourless, are characteristic of the species. If the latter be sown in a suitable medium, for example, in a solution of sugar, they swell, and shoot forth germinating utricles, which quickly grow to mycelia, which bear sporangia. This is easily produced on the most various organic bodies, and _Mucor mucedo_ is therefore found spontaneously on every substratum which is capable of nourishing mildew, but on the above-named the most perfect and exuberant specimens are generally to be found. The sporangia-bearers are at first always branchless and without partitions. After the sporangium is ripe, cross partitions in irregular order and number often appear in the inner space, and on the upper surface branches of different number and size, each of which forms a sporangium at its point. The sporangia which are formed later are often very similar, but sometimes very different, to those which first appeared, because their partition is very thick and does not fall to pieces when it is ripe, but irregularly breaks off, or remains entire, enclosing the spores, and at last falls to the ground, when the fungus withers. The cross partition which separates the sporangia from its bearers is in those which are first formed (which are always relatively thicker sporangia) very strongly convex, while those which follow later are often smaller, and in little weak specimens much less arched, and sometimes quite straight. After a few days, similar filaments generally show themselves on the dung between the sporangia-bearers, which appear to the naked eye to be provided with delicate white frills. Where such an one is to be found, two to four rectangular expanding little branches spring up to the same height round the filament. Each of these, after a short and simple process, branch out into a furcated form; the furcations being made in such a manner that the ends of the branch at last so stand together that their surface forms a ball. Finally, each of the ends of a branch swells to a little round sporangium, which is limited by a partition (called sporangiolum, to distinguish it from the larger ones), in which some, generally four, spores are formed in the manner already known. When the sporangiola are alone, they have such a peculiar appearance, with their richly-branched bearers, that they can be taken for something quite different to the organs of the _Mucor mucedo_, and were formerly not considered to belong to it. That they really belong to the _Mucor_ is shown by the principal filament which it bears, not always, but very often, ending with a large sporangium, which is characteristic of the _Mucor mucedo_; it is still more evident if we sow the spores of the sporangiolum, for, as it germinates, a mycelium is developed, which, near a simple bearer, can form large sporangia, and those form sporangiola, the first always considerably preponderating in number, and very often exclusively. If we examine a large number of specimens, we find every possible middle form between the simple or less branched sporangia-bearers and the typical sporangiola frills; and we arrive at last at the conclusion simply to place the latter among the varieties of form which the sporangia-bearer of the _Mucor mucedo_ shows, like every other typical organic form within certain limits. On the other hand, propagation organs, differing from those of the sporangia and their products, belong to _Mucor mucedo_, which may be termed conidia. On the dung (they are rare on any other substance) these appear at the same time, or generally somewhat later, than the sporangia-bearers, and are not unlike those to the naked eye. In a more accurate examination, they appear different; a thicker, partition-less filament rises up and divides itself, generally three-forked, at the length of one millimetre, into several series of branchlets. The forked branches of the last series bear under their points, which are mostly capillary, short erect little ramuli, and these, with which the ends of the principal branches articulate on their somewhat broad tops, several spores and conidia, near one another; about fifteen to twenty are formed at the end of each little ramulus. The peculiarities and variations which so often appear in the ramification need not be discussed here. After the articulation of the conidia, their bearers sink together by degrees, and are quite destroyed. The ripe conidia are round like a ball, their surface is scarcely coloured, and almost wholly smooth. These conidioid forms were at first described as a separate species under the name of _Botrytis Jonesii_. How, then, do they belong to the _Mucor_?[t] That they appear gregariously is as little proof of an original relation to one another, here as elsewhere. Attempts to prove that the conidia and sporangia-bearers originate on one and the same mycelium filament may possibly hereafter succeed. Till now this has not been the case, and he who has ever tried to disentangle the mass of filaments which exuberantly covers the substratum of a _Mucor_ vegetation, which has reached so far as to form conidia, will not be surprised that all attempts have hitherto proved abortive. The suspicion of the connection founded on the gregariously springing up, and external resemblance, is fully justified, if we sow the conidia in a suitable medium, for example, in a solution of sugar. They here germinate and produce a mycelium which exactly resembles that of the _Mucor mucedo_, and, above all, they produce in profusion the typical sporangia of the same on its bearers. The latter are till now alone reproductions of conidia-bearers, and have never been observed on mycelia which have grown out of conidia.

[Illustration: FIG. 32.--Small portion of _Botrytis Jonesii_.]

These phenomena of development appear in the _Mucor_ when it dwells on a damp substance, which must naturally contain the necessary nourishment for it, and is exposed to the atmospheric air. Its mycelium represents at first strong branched utricles without partitions; the branches are of the higher order, mostly divided into rich and very fine-pointed ramuli. In old mycelium, and also in the sporangia-bearers, the contents of which are mostly used for the formation of spores, and the substratum of which is exhausted for our fungus, short stationary pieces, filled with protoplasm, are very often formed into cells through partitions in order to produce spores, that is, grow to a new fruitful mycelium. These cells are called gemmules, brooding cells, and resemble such vegetable buds and sprouts of foliaceous plants which remain capable of development after the organs of vegetation are dead, in order to grow, under suitable circumstances, to new vegetating plants, as, for example, the bulbs of onions, &c.

If we bring a vegetating mycelium of _Mucor mucedo_ into a medium which contains the necessary nourishment for it, but excluded from the free air, the formation of sporangia takes place very sparingly or not at all, but that of gemmules is very abundant. Single interstitial pieces of the ramuli, or even whole systems of branches, are quite filled with a rich greasy protoplasm; the short pieces and ends are bound by partitions which form particular, often tun-like or globular cells; the longer ones are changed, through the formation of cross partitions, into chains of similar cells; the latter often attain by degrees strong, thick walls, and their greasy contents often pass into innumerable drops of a very regular globular form and of equal size. Similar appearances show themselves after the sowing of spores, which are capable of germinating in the medium already described, from which the air is excluded. Either short germinating utricles shoot forth, which soon form themselves into rows of gemmules, or the spores swell to large round bladders filled with protoplasm, and shoot forth on various parts of their surface innumerable protuberances, which, fixing themselves with a narrow basis, soon become round vesiculate cells, and on which the same sprouts which caused their production are repeated, formations which remind us of the fungus of fermentation called globular yeast. Among all the known forms of gemmules we find a variety which are intermediate, all of which show, when brought into a normal condition of development, the same proportion, and the same germination, as those we first described.

We have detailed rather at length the structure and development of one of the most common of the Mucors, which will serve as an illustration of the order. Other distinctions there may be which are of more interest as defining the limits of genera, except such as may be noticed when we come to write more specially of reproduction.

ASCOMYCETES.--Passing now to the _Ascomycetes_, which are especially rich in genera and species, we must first, and but superficially, allude to _Tuberacei_, an order of sporidiiferous fungi of subterranean habit, and rather peculiar structure.[u] In this order an external stratum of cells forms a kind of perithecium, which is more or less developed in different genera. This encloses the hymenium, which is sinuous, contorted, and twisted, often forming lacunæ. The hymenium in some genera consists of elongated, nearly cylindrical asci, enclosing a definite number of sporidia; in the true truffles and their immediate allies, the asci are broad sacs, containing very large and beautiful, often coloured, sporidia. These latter have either a smooth, warted, spinulose, or lacunose epispore, and, as will be seen from the figures in Tulasne's Monograph,[v] or those in the last volume of Corda's great work,[w] are attractive microscopical objects. In some cases, it is not difficult to detect paraphyses, but in others they would seem to be entirely absent. A comparatively large number have been discovered and recorded in Great Britain,[x] but of those none are more suitable for study of general structure than the ordinary truffle of the markets.

The structure of the remaining Ascomycetes can be studied under two groups, _i.e._, the fleshy Ascomycetes, or, as they have been termed, the Discomycetes, and the hard, or carbonaceous Ascomycetes, sometimes called the Pyrenomycetes. Neither of these names gives an accurate idea of the distinctions between the two groups, in the former of which the discoid form is not universal, and the latter contains somewhat fleshy forms. But in the Discomycetes the hymenium soon becomes more or less exposed, and in the latter it is enclosed in a perithecium. The Discomycetes are of two kinds, the pileate and the cup-shaped. Of the pileate such a genus as _Gyromitra_ or _Helvella_ is, in a certain sense, analogous to the Agarics amongst _Hymenomycetes_, with a superior instead of an inferior hymenium, and enclosed, not naked, spores. Again, _Geoglossum_ is somewhat analogous to _Clavaria_. Amongst the cup-shaped, _Peziza_ is an Ascomycetous _Cyphella_. But these are perhaps more fanciful than real analogies.

Recently Boudier has examined one group of the cup-shaped Discomycetes, the _Ascobolei_, and, by making a somewhat free use of his Memoir,[y] we may arrive at a general idea of the structure in the cupulate Discomycetes. They present themselves at first under the form of a small rounded globule, and almost entirely cellular. This small globule, the commencement of the receptacle, is not long in increasing, preserving its rounded form up to the development of the asci. At this period, under the influence of the rapid growth of these organs, it soon produces at its summit a fissure of the external membrane, which becomes a more marked depression in the marginate species. The receptacle thus formed increases rapidly, becomes plane, more convex, or more or less undulated at the margin, if at all of large size. Fixed to the place where it is generated by some more or less abundant mycelioid filaments, the receptacle becomes somewhat cup-shaped and either stipitate or sessile, composed of the receptacle proper and the hymenium.

[Illustration: FIG. 33.--Section of cup of _Ascobolus_. _a._ External cells. _b._ Secondary layer. _c._ Subhymenial tissue (Janczenski).]

The receptacle proper comprehends the subhymenial tissue, the parenchyma, and the external membrane. The subhymenial tissue is composed of small compact cells, forming generally a more coloured and dense stratum, the superior cells of which give rise to the asci and paraphyses. The parenchyma is seated beneath this, and is generally of interlaced filaments, of a looser consistency than the preceding, united by intermediate cellules. The external membrane, which envelopes the parenchyma, and limits the hymenium, differs from the preceding by the cells often being polyhedric, sometimes transverse, and united together, and sometimes separable. Externally it is sometimes smooth, and sometimes granular or hairy.

The hymenium is, however, the most, important part, consisting of (1) the paraphyses, (2) the asci, and sometimes (3) an investing mucilage. The asci are always present, the paraphyses are sometimes rare, and the mucilage in many cases seems to be entirely wanting.

The paraphyses, which are formed at the first commencement of the receptacle, are at first very short, but soon elongate, and become wholly developed before the appearance of the asci. They are linear, sometimes branched and sometimes simple, often more or less thickened at their tips; almost always they contain within them some oleaginous granules, either coloured or colourless. Their special function seems still somewhat obscure, and Boudier suggests that they may be excitatory organs for the dehiscence of the asci. However this may be, some mycologists are of opinion that, at least in some of the Ascomycetes, the paraphyses are abortive asci, or, at any rate, that abortive asci mixed with the paraphyses cannot be distinguished from them.

The mucilage forms itself almost at the same time as the paraphyses, and previous to the formation of the asci. This substance appears as a colourless or yellowish mucilage, which envelopes the paraphyses and asci, and so covers the hymenium with a shining coat.

The asci appear first at the base of the paraphyses, under the form of oblong cells, filled with colourless protoplasm. By rapid growth, they soon attain a considerable size and fulness, the protoplasm being gradually absorbed by the sporidia, the first indication of which is always the central nucleus. The mucilage also partly disappears, and the asci, attaining their maturity, become quite distinct, each enclosing its sporidia. But before they take their complete growth they detach themselves from the subhymenial tissue, and being attenuated towards their base, are forced upwards by pressure of the younger asci, to, and in some instances beyond, the upper surface of the disc. This phenomenon commences during the night, and continues during the night and all the morning. It attains its height at mid-day, and it is then that the slightest breath of air, the slightest movement, suffices to cause dehiscence, which is generally followed by a scarcely perceptible contractile motion of the receptacle.

[Illustration: FIG. 34.--Asci, sporidia, and paraphyses of _Ascobolus_ (Boudier).]

There is manifestly a succession in formation and maturity of the asci in a receptacle. In the true _Ascobolei_, in which the sporidia are coloured, this may be more distinctly seen. At first some thin projecting points appear upon the disc, the next day they are more numerous, and become more and more so on following days, so as to render the disc almost covered with raised black or crystalline points;[z] these afterwards diminish day by day, until they ultimately cease. The asci, after separation from the subhymenial tissue, continue to lengthen, or it may be that their elasticity permits of extension, during expulsion. Boudier considers that an amount of elasticity is certain, because he has seen an ascus arrive at maturity, eject its spores, and then make a sharp and considerable movement of retraction, then the ascus returned again, immediately towards its previous limits, always with a reduction in the number of its contained sporidia.

The dehiscence of the asci takes place in the _Ascobolei_, in some species of _Peziza_, _Morchella_, _Helvella_, and _Verpa_, by means of an apical operculum, and in other _Pezizæ_, _Helotium_, _Geoglossum_, _Leotia_, _Mitrula_, &c., by a fissure of the ascus. This operculum may be the more readily seen when the ascus is coloured by a drop of tincture of iodine.

The sporidia are usually four or eight, or some multiple of that number, in each ascus, rarely four, most commonly eight. At a fixed time the protoplasm, which at first filled the asci, disappears or is absorbed in a mucilaginous matter, which occupies its place, in the midst of which is a small nucleus, which is the rudiment of the first spore; other spores are formed consecutively, and then the substance separates into as many sections as there are sporidia. From this period each sporidium seems to have a separate existence. All have a nucleus, which is scarcely visible, often slightly granular, but which is quite distinct from the oleaginous sporidioles so frequent amongst the Discomycetes, and which are sometimes called by the same name. The sporidia are at first a little smaller than when mature, and are surrounded by mucilage. After this period the sporidia lose their nebulous granulations, whilst still preserving their nucleus; their outlines are distinct, and, amongst the true _Ascobolei_, commence acquiring a rosy colour, the first intimation of maturity. This colour manifests itself rapidly, accumulating exclusively upon the epispore, which becomes of a deep rose, then violet, and finally violet blue, so deep as sometimes to appear quite black. There are some modifications in this coloration, since, in some species, it passes from a vinous red to grey, then to black, or from rose-violet to brown.

The epispore acquires a waxy consistence by this pigmentation, so that it may be detached in granules. It is to this particular consistency of the epispore that the cracks so frequent in the coloured sporidia of _Ascobolus_ are due, through contraction of the epispore. As they approach maturity, the sporidia accumulate towards the apex of the asci, and finally escape in the manner already indicated.

In all essential particulars there is a great similarity in the structure of the other Discomycetes, especially in their reproductive system. In most of them coloured sporidia are rare. In some the receptacle is pileate, clavate, or inflated, whilst in _Stictis_ it is very much reduced, and in the lowest form of all, _Ascomyces_, it is entirely absent. In the _Phacidiacei_, the structure is very similar to that of the _Elvellacei_, whilst the _Hysteriacei_, with greater affinities with the latter, still tend towards the _Pyrenomycetes_ by the more horny nature of the receptacle, and the greater tendency of the hymenium to remain closed, at least when dry. In some species of _Hysterium_, the sporidia are remarkably fine. M. Duby[AA] has subjected this group to examination, and M. Tulasne partly so.[AB]

SPHÆRIACEI.--In this group there is considerable variation, within certain limits. It contains an immense number of species, and these are daily being augmented. The general feature in all is the presence of a perithecium, which contains and encloses the hymenium, and at length opening by a pore or ostiolum at the apex. In some the perithecia are simple, in others compound; in some immersed in a stroma, in others free; in some fleshy or waxy, in others carbonaceous, and in others membranaceous. But in all there is this important difference from the Ascomycetes we have already had under consideration, that the hymenium is never exposed. The perithecium consists usually of an external layer of cellular structure, which is either smooth or hairy, usually blackish, and an internal stratum of less compact cells, which give rise to the hymenium.

[Illustration: FIG. 35.--Perithecium of _Sphæria_ and Section.]

As in the _Discomycetes_, the hymenium consists of asci, paraphyses, and mucilage, but the whole forms a less compact and more gelatinous mass within the perithecium. The formation and growth of the asci and sporidia differ little from what we have described, and when mature the asci dehisce, and the sporidia alone are ejected from the ostiolum. We are not aware that operculate asci have yet been detected. It has been shown in some instances, and suspected in others, that certain moulds, formerly classed with _Mucedines_ and _Dematiei_, especially in the genus _Helminthosporium_, bear the conidia of species of _Sphæria_, so that this may be regarded as one form of fruit.

Perithecia, very similar externally to those of _Sphæria_, but containing spores borne on slender pedicels and not enclosed in asci, have had their relations to certain species of _Sphæria_ indicated, and these are no longer regarded so much as species of _Hendersonia_ or _Diplodia_ as the pycnidia of _Sphæria_. Other and more minute perithecia, containing minute, slender stylospores in great numbers, formerly classed with _Aposphæria_, _Phoma_, &c., but are now recognized as spermogonia containing the spermatia of _Sphæriæ_. How these influence each other, when and under what circumstances the spermatia are instrumental in impregnation of the sporidia, is still matter of mystery. It is clear, however, that in all these conidia, macrospores, microspores, and some spermatia, or by whatever names they may be called, there exists a power of germination. Tulasne has indicated in some instances five or six forms of fruit as belonging to one fungus, of which the highest and most perfect condition is a species of _Sphæria_.

[Illustration: FIG. 36.--_Uncinula adunca._]

PERISPORIACEI.--Except in the perithecia rupturing irregularly, and not dehiscing by a pore, some of the genera in this group differ little in structure from the _Sphæriacei_. On the other hand, the _Erysiphei_ present important and very interesting features. They occur chiefly on the green parts of growing plants. At first there is a more or less profuse white mycelium.[AC] This gives rise to chains of conidia (_Oidium_), and afterwards small sphæroid projections appear at certain points on the mycelium. These enlarge, take an orange colour, ultimately passing into brown, and then nearly black. Externally these perithecia are usually furnished with long, spreading, intertwined, or branching appendages, sometimes beautifully branched or hooked at their tips. In the interior of the receptacles, pear-shaped or ovate asci are formed in clusters, attached together at the base, and containing two or more hyaline sporidia. Other forms of fruit have also been observed on the same mycelium. In an exotic genus, _Meliola_, the fulcra, or appendages, as well as the mycelium, are black, otherwise it is very analogous to such a genus of _Erysiphei_ as _Microsphæria_. In _Chætomium_, the perithecia bristle with rigid, dark-coloured hairs, and the sporidia are coloured. Our limits, however, will not permit of further elucidation of the complex and varied structure to be found amongst fungi.[AD]

[A] A curious case occurred some years since at Bury St. Edmunds, which may be mentioned here in connection with the development of these nodules. Two children had died under suspicious circumstances, and an examination of the body of the latter after exhumation was made, a report having arisen that the child died after eating mushrooms. As certain white nodules appeared on the inner surface of the intestines, it was at once hastily concluded that the spores of the mushroom had germinated, and that the nodules were infant mushrooms. This appeared to one of us so strange, that application was made for specimens, which were kindly forwarded, and a cursory glance was enough to convince us that they were not fungoid. An examination under the microscope further confirmed the diagnosis, and the application of nitric acid showed that the nodules were merely due to chalk mixture, which had been given to the child for the diarrhetic symptoms under which he succumbed.

[B] Ehrenberg compared the whole structure of an Agaric with that of a mould, the mycelium corresponding with the hyphasma, the stem and pileus with the flocci, and the hymenium with the fructifying branchlets. The comparison is no less ingenious than true, and gives a lively idea of the connection of the more noble with the more humble fungi.--_Ehrb. de Mycetogenesi._

[C] In _Paxillus involutus_ the hymenium may be readily torn off and unfolded.

[D] This was well delineated in "Flora Danica," plate 834, as observed in _Coprinus comatus_ as long ago as 1780.

[E] A. de Bary, "Morphologie und Physiologie der Pilze," in "Hofmeister's Handbuch," vol. ii. cap. 5, 1866, translated in "Grevillea," vol. i. p. 181.

[F] "Die Pollinarien und Spermatien von _Agaricus_," in "Botanische Zeitung," Feb. 29 and March 7, 1856.

[G] "Essai d'une Flore mycologique de la Région de Montpellier." Paris, 1863.

[H] Hoffmann, "Botanische Zeitung," 1856, p. 139.

[I] Corda, "Icones Fungorum hucusque cognitorum," iii. p. 41. Prague, 1839.

[J] Cooke, M. C., "Anatomy of a Mushroom," in "Popular Science Review," vol. viii. p. 380.

[K] An attempt was made to show that, in _Agaricus melleus_, distinct asci were found, in a certain stage, on the gills or lamellæ. We have in vain examined the gills in various conditions, and could never detect anything of the kind. It is probable that the asci belonged to some species of _Hypomyces_, a genus of parasitic Sphæriaceous fungi.

[L] It is not intended that the spores are always quaternate in _Agaricini_, though that number is constant in the more typical species. They sometimes exceed four, and are sometimes reduced to one.

[M] The species long known as _Hydnum gelatinosum_ was examined by Mr. F. Currey in 1860 (_Journ. Linn. Soc._), and he came to the conclusion that it was not a good _Hydnum_. Since then it has been made the type of a new genus (Hydnogloea B. and Br. or, as called by Fries, in the new edition of "Epicrisis," _Tremellodon_, Pers. Myc. Eur.), and transferred to the _Tremellini_. Currey says, upon examining the fructification, he was surprised to find that, although in its external characters it was a perfect _Hydnum_, it bore the fruit of a _Tremella_. If one of the teeth be examined with the microscope, it will be seen to consist of threads bearing four-lobed sporophores, and spores exactly similar to _Tremella_. It will thus be seen, he adds, that the plant is exactly intermediate between _Hydnei_ and _Tremellini_, forming, as it were, a stepping-stone from one to the other.

[N] Tulasne, L. R. and C., "Observations on the Organization of the Tremellini," in "Ann. des Sci. Nat." 3^me sér. xix. (1853), pp. 193, &c.

[O] M. Léveillé, in "Ann. des Sci. Nat." 2^me sér. viii. p. 328; 3^me sér. ix. p. 127; also Bonorden, "Handbuch der Mycologie," p. 151.

[P] Tulasne, in "Ann. des Sci. Nat." (loc. cit.) xix. pl. x. fig. 29. Tulasne, "New Notes upon Tremellinous Fungi," in "Journ. Linn. Soc." vol. xiii. (1871), p. 31.

[Q] Berkeley, M. J., "On the Fructification of Lycoperdon, Phallus, &c.," in "Ann. Nat. Hist." 1840, vol. iv. p. 158, pl. 5. Berkeley, M. J., "Introduction Crypt. Bot." p. 346.

[R] Tulasne, L. R. and C., "Fungi Hypogæi." Paris. Berkeley and Broome, "British Hypogæous Fungi," in "Ann. Nat. Hist." 1846, xviii. p. 74. Corda, "Icones Fungorum," vol. vi. pl. vii. viii.

[S] Tulasne, "Sur le Genre _Secotium_," in "Ann. des Sci. Nat." (1845), 3^me sér. vol. iv. p. 169, plate 9.

[T] Tulasne, L. R. and C., "De la Fructification des _Scleroderma_ comparée a celle des _Lycoperdon_ et des _Borista_," in "Ann. des Sci. Nat." 1842, xvii. p. 5. Tulasne, L. R. and C., "Sur les Genres Polysaccum et Geaster," in "Ann. des Sci. Nat." 1842, xviii. p. 129, pl. 5 and 6.

[U] Berkeley, "On the Fructification of Lycoperdon, &c.," in "Annals of Natural History" (1840), iv. p. 155.

[V] Wigand, "Morphologie des Genres Trichia et Arcyria," in "Ann. des Sci. Nat." 4^me sér. xvi. p. 223.

[W] Currey, "On Spiral Threads of Trichia," in "Quart. Journ. Micr. Science" (1855), iii. p. 17.

[X] In some of the genera, as, for instance, in _Badhamia_, _Enerthenema_, and _Reticularia_, the spores are produced within delicate cells or cysts, which are afterwards absorbed.

[Y] Tulasne, "Essai d'une Monographie des Nidulariées," in "Ann. des Sci. Nat." (1844), i. 41 and 64.

[Z] Berkeley, M. J., "Introduction, Crypt. Bot." p. 330.

[a] Berkeley, M. J., "Introduction, Crypt. Bot." p. 329.

[b] In the _Cæomacei_ and _Pucciniæi_ the term "pseudospore" would be much more accurate.

[c] Léveillé, "Sur la Disposition Méthodique des Urédinées," in "Ann. des Sci. Nat." (1847), vol. viii. p. 369.

[d] De Bary, "Champignons Parasites," in "Ann. des Sci. Nat." 4^me sér. vol. xx.

[e] Tulasne, "Mémoire sur les Urédinées, &c.," in "Ann. des Sci. Nat." (1854), vol. ii. p. 78.

[f] De Bary, "Ueber die Brandpilze," Berlin, 1853.

[g] Currey, in "Quart. Journ. Micr. Sci." (1857), vol. v. p. 119, pl. 8, fig 13.

[h] Cooke, "On Podisoma," in "Journal of Quekett Microscopical Club," vol. ii. p. 255.

[i] Tulasne, "Mémoire sur les Ustilaginées," in "Ann. des Sci. Nat." (1847), vii. pp. 12 and 73.

[j] Corda, "Icones Fungorum," vol. iii. fig. 45.

[k] Cooke, "On Podisoma," in "Quekett Journal," vol. ii. p. 255.

[l] It may be a question whether _Graphiola_ is not more nearly allied to _Trichocoma_ (Jungh Fl. Crypt. Javæ, p. 10, f. 7) than to the genera with which it is usually associated.--M. J. B.

[m] Cooke, "On Microscopic Moulds," in "Quekett Journal," vol. ii. plate 7.

[n] _See_ "Dendryphium Fumosum," in "Quekett Journal," vol. ii. plate 8; or, "Corda Prachtflora," plate 22.

[o] De Bary, "Champignons Parasites," in "Ann. des Sci. Nat." 4^me sér. vol. xx.

[p] Berkeley, "On the Potato Murrain," in "Journ. of Hort. Soc. of London," vol. i. (1846), p. 9.

[q] De Bary, "On Mildew and Fermentation," p. 25, reprinted from "German Quarterly Magazine," 1872; De Bary, "Morphologie und Physiologie der Pilze," (1866), 201.

[r] Cooke, "Handbook of British Fungi," vol. ii. p. 552.

[s] De Bary, "On Mildew and Fermentation," in "Quarterly German Magazine," for 1872.

[t] We are quite aware that Von Tieghem and Le Monnier, in "Ann. des Sci. Nat." 1873, p. 335, dispute that this belongs to _Mucor mucedo_, and assert that _Chætocladium Jonesii_ is itself a true _Mucor_, with monosporous sporangia.

[u] Vittadini, "Monographia Tuberacearum," 1831.

[v] Tulasne, "Fungi Hypogæi," 1851.

[w] Corda, "Icones Fungorum," vol. vi.

[x] Berkeley and Broome, in "Ann. of Nat. Hist." 1st ser. vol. xviii. (1846), p. 73; Cooke, in "Seem. Journ. Bot."

[y] Boudier (E.), "Mémoire sur les Ascobolés," in "Ann. des Sci. Nat." 5^me sér. vol. x. (1869).

[z] Only in some of the Discomycetes are the asci exserted.

[AA] Duby, "Mémoire sur la Tribu des Hysterinées," 1861.

[AB] Tulasne, "Selecta Fungorum Carpologia," vol. iii.

[AC] Tulasne, "Selecta Fungorum Carpologia," vol. i. Léveillé, "Organisation, &c., sur l'Érysiphé," in "Ann. des Sci. Nat." (1851), vol. xv. p. 109.

[AD] Other works besides those already cited, which may be consulted with advantage on structure, are--

Tulasne, L. R. and C., various articles in "Annales des Sciences Naturelles," série iii. and iv.

Hoffmann, "Icones Analyticæ Fungorum."

De Bary, "Der Ascomyceten." Leipzic, 1863.

Berkeley, M. J., "Introduction to Cryptogamic Botany."

Seynes, J. de, "Recherches, &c., des Fistulines." Paris, 1874.

Winter, G., "Die Deutschen Sordarien." 1874.

Corda, J., "Prachtflora." Prague, 1840.

De Bary, "Über der Brandpilze." 1853.

Brefeld, O., "Botan. Untersuch. ü Schimmelpilze."

Fresenius, G., "Beiträge zur Mykologie." 1850.

Von Tieghem and Le Monnier, in "Annales des Sciences Naturelles" (1873), p. 335.

Cornu, M., "Sur les Saprolegniées," in "Ann. des Sci. Nat." 5^me sér. xv. p. 5.

Janczenski, "Sur l'Ascobolus furfuraceus," in "Ann. des Sci. Nat." 5^me sér. xv. p. 200.

De Bary and Woronin, "Beiträge zur Morphologie und Physiologie der Pilze." 1870.

Bonorden, H. F., "Abhandlungen aus dem Gebiete der Mykologie." 1864.

Coemans, E., "Spicilége Mycologique." 1862, etc.

III

CLASSIFICATION

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.

[Illustration: FIG. 37.--_Agaricus nudus._]

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.

[Illustration: FIG. 38.--_Scleroderma vulgare_, Fr.]

[Illustration: FIG. 39.--_Ceuthospora phacidioides_ (Greville).]

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.

[Illustration: FIG. 40.--_Rhopalomyces candidus._]

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.

[Illustration: FIG. 41.--_Mucor caninus._]

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.

[Illustration: FIG. 42.--_Sphæria aquila._]

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."

[A] Rev. M. J. Berkeley, "Introduction to Cryptogamic Botany" (1857), London, pp. 235 to 372.

[B] De Bary, in "Streinz Nomenclator Fungorum," p. 722.

[C] Tulasne, L. and C. R., "Observations sur l'Organisation des Trémellinées," "Ann. des Sci. Nat." 1853, xix. p. 193.

[D] Berkeley, M. J., "On the Fructification of _Lycoperdon_, _Phallus_, and their Allied Genera," in "Ann. of Nat. Hist." (1840), vol. iv. p. 155; "Ann. des Sci. Nat." (1839), xii. p. 163. Tulasne, L. R. and C., "De la Fructification des _Scléroderma_ comparée à celle des _Lycoperdon_ et des _Bovista_," in "Ann. des Sci. Nat." 2^me sér. xvii. p. 5.

[E] Tulasne, L. R. and C., "Fungi Hypogæi," Paris, 1851; "Observations sur le Genre Elaphomyces," in "Ann. des Sci. Nat." 1841, xvi. 5.

[F] _Stapeliæ_ in this respect approach most closely to the _Phalloidei_.

[G] Berkeley, in "Ann. Nat. Hist." vol. iv. p. 155.

[H] Tulasne, L. R. and C., "Recherches sur l'Organisation et le Mode de Fructification des Nidulariées," "Ann. des Sci. Nat." (1844), i. p. 41.

[I] De Bary, A., "Des Myxomycètes," in "Ann. des Sci. Nat." 4^me sér. xi. p. 153; "Bot. Zeit." xvi. p. 357.

[J] Corda, "Icones Fungorum," vol. iii. fig. 45.

[K] Tulasne, "Mémoire sur les Ustilaginées," "Ann. des Sci. Nat." (1847), vii. 12-73.

[L] Tulasne, "Mémoire sur les Urédinées," "Ann. des Sci. Nat." (1854), ii. 78.

[M] Tulasne, "Sur les Urédinées," "Ann. des Sci. Nat." 1854, ii. pl. 9.

[N] Cooke, M. C., "Notes on _Podisoma_," in "Journ. Quek. Micr. Club," No. 17 (1871), p. 255.

[O] Tulasne, L. R. and C., "Selecta Fungorum Carpologia," vol. iii. pp. 4-19.

[P] De Bary, A., "Recherches sur les Champignons Parasites," in "Ann. des Sci. Nat." 4^me sér. xx. p. 5; "Grevillea," vol. i. p. 150.

[Q] A. de Bary, translated in "Grevillea," vol. i. p. 167; Tulasne, "Ann. des Sci. Nat." 5^me sér. (1866), p. 211.

[R] Léveillé, J. H., "Organisation, &c., de l'Érysiphé," in "Ann. des Sci. Nat." (1851), xv. p. 109.

[S] Tulasne, L. R. and C., "Fungi Hypogæi," Paris; Vittadini, C., "Monographia Tuberacearum," Milan, 1831.

[T] "A Currant Twig and Something on it," in "Gardener's Chronicle" for January 28, 1871.

[U] Berkeley, M. J., "Introduction to Cryptogamic Botany," London, 1857; Cooke, M. C., "Handbook of British Fungi," London, 1871 ; Corda, A. C. J., "Anleitung zum Studium der Mycologie," Prag, 1842; Kickx, J., "Flore Cryptogamique des Flanders," Gand, 1867; Fries, E., "Systema Mycologicum," Lund, 1830; Fries, E., "Summa Vegetabilium Scandinaviæ," 1846; Secretan, L., "Mycographie Suisse," Geneva, 1833; Berkeley, M. J., "Outlines of British Fungology," London, 1860.

TABULAR ARRANGEMENT OF FAMILIES AND ORDERS.

DIVISION I. SPORIFERA. _Spores naked._

I. Hymenium free, mostly naked, or soon exposed HYMENOMYCETES. Hymenium normally inferior-- Fruit-bearing surface lamellose _Agaricini._ Fruit-bearing surface porous or tubular _Polyporei._ Fruit-bearing surface clothed with prickles _Hydnei._ Fruit-bearing surface even or rugose _Auricularini._ Hymenium superior or encircling-- Clavate, or branched, rarely lobed _Clavariei._ Lobed, convolute, or disc-like, gelatinous _Tremellini._

II. Hymenium enclosed in a peridium, ruptured when mature GASTEROMYCETES. Hymenomycetous-- Subterranean, naked or enclosed _Hypogæi._ Terrestrial, hymenium deliquescent _Phalloidei._ Peridium enclosing sporangia, containing spores _Nidulariacei._ Coniospermous-- Stipitate, hymenium convolute, drying into a dusty mass, enclosed in a volva _Podaxinei._ Cellular at first, hymenium drying up into a dusty mass of threads and spores _Trichogastres._ Gelatinous at first, peridium containing at length a dusty mass of threads and spores _Myxogastres._

III. Spores naked, mostly terminal, on inconspicuous threads, free or enclosed in a perithecium CONIOMYCETES. Growing on dead or dying plants-- Subcutaneous-- Perithecium more or less distinct _Sphæronemei._ Perithecium obsolete or wanting _Melanconiei._ Superficial-- Fructifying surface naked. Spores compound or tomiparous _Torulacei._ Parasitic on living plants-- Peridium distinctly cellular _Æcidiacei._ Peridium none-- Spores sub-globose, simple or deciduous _Cæomacei._ Spores mostly oblong, usually septate _Pucciniæi._

IV. Spores naked, on conspicuous threads, rarely compacted, small HYPHOMYCETES. Fertile threads compacted, sometimes cellular-- Stem or stroma compound-- Spores dry, volatile _Isariacei._ Mass of spores moist, diffluent _Stilbacei._ Fertile threads, free or anastomosing-- Fertile threads dark, carbonized-- Spores mostly compound _Dematiei._ Fertile threads not carbonized-- Very distinct-- Spores mostly simple _Mucedines._ Scarcely distinct from mycelium-- Spores profuse _Sepedoniei._

DIVISION II. SPORIDIIFERA. _Sporidia in Asci._

V. Fertile cells seated on threads, not compacted into a hymenium PHYSOMYCETES. Threads felted, moniliform-- Sporangia irregular _Antennariei._ Threads free-- Sporangia terminal or lateral _Mucorini._ Aquatic _Saprolegniei._

VI. Asci formed from the fertile cells of a hymenium ASCOMYCETES. Asci often evanescent-- Receptacle clavæform-- Asci springing from threads _Onygenei._ Perithecia free-- Asci springing from the base _Perisporiacei._ Asci persistent-- Perithecia opening by a distinct ostiolum _Sphæriacei._ Hard or coriaceous, hymenium at length exposed _Phacidiacei._ Hypogæous; hymenium complicated _Tuberacei._ Fleshy, waxy, or tremelloid; hymenium mostly exposed _Elvellacei._