M. C. Cooke

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.

Fig. 1.

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.

Fig. 2.

Fig. 2.—Section of Common Mushroom.

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.

Fig. 3.

Fig. 3.—a. Sterile cells. b. Basidia. c. Cystidium. From Gomphidius (de Seynes).

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.

Fig. 4.

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.

Fig. 5.

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.

Fig. 6.

Fig. 6.—Calocera viscosa.

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.

Fig. 7.

Fig. 7.—Tremella mesenterica.

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]

Fig. 8.

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.

Fig. 9.

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.

Fig. 10.

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.

Fig. 11.

Fig. 11.—Arcyria incarnata, with portion of threads and spore, magnified.

Fig. 12.

Fig. 12.—DiachÆa elegans.

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.

Fig. 13.

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.

Fig. 14.—Cyathus. a. Sporangium. b. Section. c. Sporophore. d. Spores.

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.

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]

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.

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]

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.

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.

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 Œrsted 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]

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.

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.

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.

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.

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.

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.

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.

Fig. 33.—Section of cup of Ascobolus. a. External cells. b. Secondary layer. c. Subhymenial tissue (Janczenski).