A work of this character would hardly be deemed complete without some reference to the above subject, which has moreover a relation to some of the questions discussed, and particularly of spore diffusion in the atmosphere. The largest spore is microscopic, and the smallest known scarcely visible under a magnifying power of 360 diameters. Taking into account the large number of species of fungi, probably scarcely less numerous than all the flowering plants, and the immense number of spores which some of the individuals produce, they must be exceedingly plentiful and widely diffused, though from their minuteness not easy to be discerned. It has been attempted to estimate the number of spores which might be produced by one single plant of Lycoperdon, but the number so far exceeds that which the mind is accustomed to contemplate that it seems scarcely possible to realize their profusion. Recent microscopic examinations of the common atmosphere[A] show the large quantity of spores that are continually suspended. In these investigations it was found that spores and similar cells were of constant occurrence, and were generally present in considerable numbers. That the majority of the cells were living, and ready to undergo development on meeting with suitable conditions, was very manifest, as in those cases in which preparations were retained under observation for any length of time, germination rapidly took place in many of the cells. In few instances did any development take place, beyond the formation of networks of mycelium, or masses of toruloid cells, but, in one or two, distinct sporules were developed on the filaments arising from some of the larger septate spores; and in a few others, Penicillium and Aspergillus produced their characteristic heads of fructification. With regard to the precise nature of the spores, and other cells present in various instances, little can be said, as, unless their development were to be carefully followed out through all its stages, it is impossible to refer them to their correct species or even genera. The greater number of them are apparently referable to the old orders of fungi, SphÆronemei, Melanconei, Torulacei, Dematiei and Mucedines, while some probably belonged to the PucciniÆi and CÆomacei.

Hence it is demonstrated that a large number of the spores of fungi are constantly present in the atmosphere, which is confirmed by the fact that whenever a suitable pabulum is exposed it is taken possession of by floating spores, and soon converted into a forest of fungoid vegetation. It is admitted that the spores of such common moulds as Aspergillus and Penicillium are so widely diffused, that it is almost impossible to exclude them from closed vessels, or the most carefully guarded preparations. Special contrivances for the dispersion of the spores in the different groups follow a few general types, and it is only rarely that we meet with any method that is confined only to a species or genus. Some of the more significant forms of spores may be illustrated, with their modes of dissemination.

Basidiospores is a term which we may employ here to designate all spores borne at the tips of such supports as are found in the Hymenomycetes and Gasteromycetes, to which the name of basidia has been given. In fact, under this section we may include all the spores of those two orders, although we may be ignorant of the precise mode in which the fruit of most of the Myxogastres is developed. Guarding ourselves at the outset against any misinterpretation as to the use of this term, which, in fact, we employ simply to designate the fruit of Hymenomycetes, we may have excuse in our desire to limit special terms as much as possible. In the Agaricini the spores are plentiful, and are distributed over the hymenium or gill plates, the surface of which is studded with basidia, each of which normally terminates with four short, erect, delicate, thread-like processes, each of which is surmounted by a spore. These spores are colourless or coloured, and it is upon this fact that primary divisions in the genus Agaricus are based, inasmuch as colour in the spores appears to be a permanent feature. In white-spored species the spores are white in all the individuals, not mutable as the colour of the pileus, or the corolla in phanerogamic plants. So also with the pink spored, rusty spored, black spored, and others. This may serve to explain why colour, which is so little relied upon in classification amongst the higher plants, should be introduced as an element of classification in one of the largest genera of fungi.

There are considerable differences in size and form amongst the spores of the Agaricini, although at first globose; when mature they are globose, oval, oblong, elliptic, fusiform, and either smooth or tuberculated, often maintaining in the different genera or subgenera one particular characteristic, or typical form. It is unnecessary here to particularize all the modifications which the form and colour of the spores undergo in different species, as this has already been alluded to. The spores in the Polyporei, Hydnei, &c., are less variable, of a similar character, as in all the Hymenomycetes, except perhaps the Tremellini.

When an Agaric is mature, if the stem is cut off close to the gills, and the pileus inverted, with the gills downwards on a sheet of black paper (one of the pale-spored species is best for this purpose), and left for a few hours, or all night, in that position, the paper will be found imprinted in the morning with a likeness of the under side of the pileus with its radiating gills, the spores having been thrown down upon the paper in such profusion, from the hymenium, and in greater numbers from the opposed surfaces of the gills. This little experiment will be instructive in two or three points. It will illustrate the facility with which the spores are disseminated, the immense number in which they are produced, and the adaptability of the gill structure to the economy of space, and the development of the largest number of basidiospores from a given surface. The tubes or pores in Polyporei, the spines in Hydnei, are modifications of the same principles, producing a like result.

In the Gasteromycetes the spores are produced in many cases, probably in most, if not all, at the tips of sporophores; but the hymenium, instead of being exposed, as in the Hymenomycetes, is enclosed within an outer peridium or sac, which is sometimes double. The majority of these spores are globose in form, some of them extremely minute, variously coloured, often dark, nearly black, and either externally smooth or echinulate. In some genera, as Enerthenema, Badhamia, &c., a definite number of spores are at first enclosed in delicate cysts, but these are exceptions to the general rule: this also is the case in at least one species of Hymenogaster. As the spores approach maturity, it may be observed in such genera as Stemonitis, Arcyria, Diachea, Dictydium, Cribraria, Trichia, &c., that they are accompanied by a sort of reticulated skeleton of threads, which remain permanent, and served in earlier stages, doubtless, as supports for the spores; being, in fact, the skeleton of the hymenium. It has been suggested that the spiral character of the threads in Trichia calls to mind the elaters in the HepaticÆ, and like them may, by elasticity, aid in the dispersion of the spores. There is nothing known, however, which will warrant this view. When the spores are mature, the peridium ruptures either by an external orifice, as in Geaster, Lycoperdon, &c., or by an irregular opening, and the light, minute, delicate, spores are disseminated by the slightest breath of air. Specimens of Geaster and Bovista are easily separated from the spot on which they grew; when rolling from place to place, the spores are deposited over a large surface. In the Phalloidei the spores are involved in a slimy mucus which would prevent their diffusion in such a manner. This gelatinous substance has nevertheless a peculiar attraction for insects, and it is not altogether romantic to believe that in sucking up the fetid slime, they also imbibe the spores and transfer them from place to place, so that even amongst fungi insects aid in the dissemination of species. Whether or not the Myxogastres should be included here is matter of opinion, since the mode in which the spores are developed is but little known; analogy with the Trichogastres in other points alone leading to the conclusion that they may produce basidiospores. The slender, elastic stems which support the peridia in many species are undoubted aids to the dissemination of the spores.[B]

Under the name of Stylospores may be classed those spores which in some orders of Coniomycetes are produced at the apex of short threads, either enclosed in a perithecium, or seated upon a kind of stroma. These are exceedingly variable, sometimes large, and multiseptate, at other times minute, resembling spermatia. In such genera as are chiefly epiphytal, in Septoria, Phyllosticta, and their allies, the minute spores are enclosed within membranaceous perithecia, and when mature these are ejected from the orifice at the apex, or are exposed by the breaking off of the upper portion of the perithecia. In Diplodia and Hendersonia the spores are larger, mostly coloured, often very fine in the latter genus, and multiseptate, escaping from the perithecia by a terminal pore. Probably the species are only pycnidia of SphÆriacei, but that is of no consequence in relation to our present inquiry. Of stylospores which deserve mention on account of their singularity of form, we may note those of Dilophospora graminis, which are straight, and have two or three hair-like appendages at each extremity. In Discosia there is a single oblique bristle at each end, or at the side of the septate spores, whilst in Neottiospora a tuft of delicate hairs is found at one extremity only. The appendages in Dinemasporium are similar to those of Discosia. The spores in Prosthemium may be said in some sort to resemble compound Hendersonia, being fusiform and multiseptate, often united at the base in a stellate manner. In this genus, as in Darluca, Cytispora, and the most of those belonging to the Melanconiei, the spores when mature are expelled from the orifice of the perithecium or spurious perithecium, either in the form of tendrils, or in a pasty mass. In these instances the spores are more or less involved in gelatine, and when expelled lie spread over the matrix, around the orifice; their ultimate diffusion being due to moisture washing them over other parts of the same tree, since it is probable that their natural area of dissemination is not large, the higher plants, of which they are mostly conditions, being developed on the same branches. More must be known of the relations between Melanconium and Tulasne’s sphÆriaceous genus Melanconis before we can appreciate entirely the advantage to Melanconium and some other genera, that the wide diffusion of their spores should be checked by involving them in mucus, or their being agglutinated to the surface of the matrix, only to be softened and diffused by rain. The spores in many species amongst the Melanconiei are remarkably fine; those of Stegonosporium have the endochrome partite and cellular. In Stilbospora and Coryneum the spores are multiseptate, large, and mostly coloured. In Asterosporium the spores are stellate, whilst in Pestalozzia they are septate, with a permanent peduncle, and crested above with two or three hyaline appendages.

The Torulacei externally, and to the naked eye, are very similar to the black moulds, and the mode of dissemination will be alike in both. The spores are chiefly compound, at first resembling septate threads, and at length breaking up into joints, each joint of which possesses the function of a spore. In some instances the threads are connate, side by side, as in Torula hysterioides, and in Speira, being concentrically arranged in laminÆ in the latter genus. The structure in Sporochisma is very peculiar, the joints breaking up within an external tube or membrane. The spores in Sporidesmium appear to consist of irregular masses of cells, agglomerated into a kind of compound spore. Most of the species become pulverulent, and the spores are easily diffused through the air like an impalpable dust. They form a sort of link between the stylospores of one section of the Coniomycetes, and the pseudospores of the parasitical section.

Pseudospore is, perhaps, the most fitting name which can be applied to the so-called spores of the parasitical Coniomycetes. Their peculiar germination, and the production of reproductive bodies on the germ tubes, prove their analogy to some extent with the prothallus of other cryptogams, and necessitate the use of some term to distinguish them from such spores as are reproductive without the intervention of a promycelium. The differences between these pseudospores in the several genera are confined in some instances to their septation, in others to their mode of development. In the Æcidiacei the pseudospores are more or less globose, produced in chains within an external cellular peridium. In the CÆomacei they are simple, sometimes produced in chains, and sometimes free, with or without a caduceous peduncle. In the Ustilaginei they are simple, dark coloured, and occasionally attached in subglobose masses, as in Urocystis and Thecaphora, which, are more or less compact. In the PucciniÆi the distinctive features of the genera are based upon the more or less complex nature of the pseudospores, which are bilocular in Puccinia, trilocular in Triphragmium, multilocular in Phragmidium, &c. In the curious genus Podisoma the septate pseudospores are involved in a gelatinous element. The diffusion of these fruits is more or less complete according to their compact or pulverulent nature. In some species of Puccinia the sori are so compact that they remain attached to the leaves long after they are dead and fallen. In the genus Melampsora, the wedge-shaped winter-pseudospores are not perfected until after the dead leaves have for a long time remained and almost rotted on the ground. It is probable that their ultimate diffusion is only accomplished by the rotting and disintegration of the matrix. In the CÆomacei, Ustilaginei, and Æcidiacei the pseudospores are pulverulent, as in some species of Puccinia, and are easily diffused by the motion of the leaves in the wind, or the contact of passing bodies. Their diffusion in the atmosphere seems to be much less than in the case of the Hyphomycetes. By what means such a species as Puccinia malvacearum, which has very compact sori, has become within so short a period diffused over such a wide area, is a problem which in the present state of our knowledge must remain unsolved. It may be through minute and plentiful secondary spores.

Spermatia are very minute delicate bodies found associated with many of the epiphyllous Coniomycetes, and it has been supposed are produced in conjunction with some of the SphÆriacei, but their real function is at present obscure, and the name is applied rather upon conjecture than knowledge. It is by no means improbable that spermatia do exist extensively amongst fungi, but we must wait in patience for the history of their relationship.

Trichospores might be applied better, perhaps, than conidia to the spores which are produced on the threads of the Hyphomycetes. Some of them are known to be the conidia of higher plants; but as this is by no means the case with all, it would be assuming too much to give the name of conidia to the whole. By whatever name they may be called, the spores of the Hyphomycetes are of quite a different type from any yet mentioned, approximating, perhaps, most closely to the basidiospores of the Hymenomycetes in some, and Gasteromycetes in others; as, for instance, in the Sepedoniei and the Trichodermacei. The form of the spores and their size differ materially, as well as the manner in which they are produced on the threads. In many they are very minute and profuse, but larger and less plentiful in the Dematiei than in the Mucedines. The spores of some species of Helminthosporium are large and multiseptate, calling to mind the spores of the Melanconiei. Others are very curious, being stellate in Triposporium, circinate in Helicoma and Helicocoryne, angular in Gonatosporium, and ciliate in Menispora ciliata. Some are produced singly and some in chains, and in some the threads are nearly obsolete. In Peronospora, it has been demonstrated that certain species produce minute zoospores from the so-called spores. The dissemination of the minute spores of the Mucedines through the air is undoubted; rain also certainly assists not only in the dispersion of the spores in this as in other groups, but also in the production of zoospores which require moisture for that purpose. The form of the threads, and the mode of attachment of the spores, is far more variable amongst the Mucedines than the form of the spores, but the latter are in all instances so slightly attached to their supports as to be dissevered by the least motion. This aids also in the diffusion of the spores through the atmosphere.

Sporangia are produced in the Physomycetes usually on the tips or branches of delicate threads, and these when mature dehisce and set free the minute sporidia. These are so small and uniform in their character that they require but a passing mention. The method of diffusion agrees much with that of the Mucedines, the walls of the sporangia being usually so thin and delicate as to be easily ruptured. Other modes of fructification prevail in some species by the production of cysts, which are the result of conjugation of the threads. These bodies are for the most part furnished with thicker and more resistant walls, and the diffusion of their contents will be regulated by other circumstances than those which influence the dispersion of the minute sporidia from the terminal cysts. Probably they are more perennial in their character, and are assimilated more to the oogonia of Cystopus and Peronospora, being rather of the nature of resting spores, inasmuch as the same threads usually bear the terminal fruits.

Thecaspores is a term which may be applied generally to all sporidia produced in asci, but these are in turn so innumerable and variable that it will be necessary to treat of some of the groups individually. The Thecaspores, for instance, of the Tuberacei offer several features whereby they may be distinguished from other thecaspores. The asci in which these sporidia are generated mostly partake of a broadly saccate, ovate form. The number of sporidia contained in an individual ascus is usually less than in the majority of the Ascomycetes, and the sporidia approximate more nearly to the globose form. Usually, also, they are comparatively large. Many have been figured by Corda[C] and Tulasne.[D] Three types of spores may be said to prevail in the Tuberacei: the smooth spored, the warted or spinulose, and the areolate. The first of these may be represented by the Stephensia bombycina, in which the globose sporidia are quite smooth and colourless. The warted sporidia may be observed in Genea verrucosa, the spinulose in Tuber nitidum, and the areolate are present in Tuber Æstivum and Tuber excavatum, in which the epispore is divided into polygonal alveoli, bounded by thin, membranaceous, prominent partitions. This form of sporidium is very beautiful. In all no special provision is made for the dissemination of the sporidia, as, from their subterranean habit, none would be available save the ultimate dissolution of the external integuments. As they are greedily devoured by several animals, it is possible that they may be dispersed through the excrements.

In the Perisporiacei the perithecium has no proper orifice, or ostiolum, for the discharge of the mature sporidia, which are usually small, and are disseminated by the irregular rupture of the somewhat fragile conceptacles. The asci are usually more or less saccate, and the sporidia approximate to a globose form. The asci are often very diffluent. In Perisporium vulgare the ovate brown sporidia are at first, and for some time, attached together in fours in a concatenate or beaded manner. In some species of Erysiphei the conceptacle encloses but a single sporangium, in others several, which are attached together at the base. In some species the sporangia contain two, in others four, in others eight, and in others numerous sporidia. In ChÆtomium the asci are cylindrical, and in most cases the coloured sporidia are lemon-shaped. When the conceptacles are fully matured, it is commonly the case that the asci are absorbed and the sporidia are free in the interior of the conceptacles.

Of the fleshy Discomycetes the genus Peziza may be taken as the type. If the structure which prevails in this genus be brought to mind, it will be remembered that the hymenium lines an expanded cup, and that the asci are packed together, side by side, with their apices outwards, and their bases attached to a substratum of cells which form the inner layer of the receptacle. The sporidia are usually eight in each ascus, either arranged in single or double rows, or irregularly grouped together. The asci are produced in succession; the later, pressing themselves upwards between those previously developed, cause the rupture of the mature asci at the apex and the ejection of the sporidia with considerable force. When a large Peziza is observed for a time a whitish cloud will be seen to rise suddenly from the surface of the disc, which is repeated again and again whenever the specimen is moved. This cloud consists of sporidia ejected simultaneously from several asci. Sometimes the ejected sporidia lie like frost on the surface of the disc. Theories have been devised to account for this sudden extrusion of the sporidia, in Ascobolus, and a few species of Peziza, of the asci also, the most feasible one being the successive growth of the asci; contraction of the cup may also assist, as well as some other less potent causes. It may be remarked here that the sporidia in Peziza and Helotium are mostly colourless, whilst in Ascobolus they pass through pink to violet, or dark brown, and the epispore, which is of a waxy nature, becomes fissured in a more or less reticulated manner.

The sporidia in Hysterium proper are usually coloured, often multiseptate, sometimes fenestrate, and occasionally of considerable size. There is no evidence that the sporidia are ever excluded in the same manner as in Peziza, the lips closing over the disc so much as to prevent this. The diffusion of the sporidia probably depends on the dissolution of the asci, and hence they will not be widely dispersed, unless, perhaps, by the action of rain.

In Tympanis, asci of two kinds have been observed in some species; one kind containing an indefinite number of very minute bodies resembling spermatia, and the other octosporous, containing sporidia of the usual type.

The SphÆriacei include an almost infinite variety in the form and character of the sporidia. Some of these are indefinite in the number contained in an ascus, although the majority are eight, and a few less. In the genera Torrubia and Hypocrea the structure differs somewhat from other groups, inasmuch as in the former the long thread-like sporidia break up into short joints, and in the latter the ascus contains sixteen subglobose or subquadrate sporidia. Other species contain linear sporidia, which are often the length of the ascus, and may either be simple or septate. In SphÆria ulnaspora the sporidia are abruptly bent at the second joint. Shorter fusiform sporidia are by no means uncommon, varying in the number of septa, and in constriction at the joints in different species. Elliptic or ovate sporidia are common, as are those of the peculiar form which may be termed sausage-shaped. These are either hyaline or coloured of some shade of brown. Coloured sporidia of this kind are common in Xylaria and Hypoxylon, as well as in certain species of the section Superficiales. Coloured sporidia are often large and beautiful: they are mostly of an elongated, elliptical form, or fusiform. As noteworthy may be mentioned the sporidia of Melanconis lanciformis, those of Valsa profusa, and some species of Massaria, the latter being at first invested with a hyaline coat. Some coloured sporidia have hyaline appendages at each extremity, as in Melanconis Berkeleii, and an allied species, Melanconis bicornis, from the United States, also some dung SphÆriÆ, as S. fimiseda, included under the proposed genus Sordaria.[E] Hyaline sporidia occasionally exhibit a delicate bristle-like appendage at each extremity, as in the Valsa thelebola, or with two additional cilia at the central constriction, as in Valsa taleola. A peculiar form of sporidium is present in certain species of SphÆria found on dung, for which the generic name of Sporormia has been proposed, in which the sporidium (as in Perisporium vulgare) consists of four coloured ovate joints, which ultimately separate. Multiseptate fenestrate sporidia are not uncommon in Cucurbitaria and Pleospora, as well as in Valsa fenestrata and some other species. In the North American SphÆria putaminum the sporidia are extraordinarily large.

The dissemination of the sporidia may, from identity of structure in the perithecium, be deemed to follow a like method in all. When mature, they are in a great measure expelled from the mouth of the perithecia, as is evident in species with large dark sporidia, such as exist in the genera Hypoxylon, Melanconis, and Massaria. In these genera the sporidia, on maturity, may be observed blackening the matrix round the mouths of the perithecia. As moisture has an evident effect in producing an expulsion of sporidia by swelling the gelatinous nucleus, it may be assumed that this is one of the causes of expulsion, and therefore of aids to dissemination. When SphÆriÆ are submitted to extra moisture, either by placing the twig which bears them on damp sand, or dipping one end in a vessel of water, the sporidia will exude and form a gelatinous bead at the orifice. There may be other methods, and possibly the successive production of new asci may also be one, and the increase in bulk by growth of the sporidia another; but of this the evidence is scanty.

Finally, Oogonia may be mentioned as occurring in such genera as Peronospora amongst moulds, Cystopus amongst Uredines, and the SaprolegniaceÆ amongst the Physomycetes. The zoospores being furnished with vibratile cilia, are for some time active, and need only water in which to disseminate themselves, and this is furnished by rain.

We have briefly indicated the characteristics of some of the more important types of spores to be found in fungi, and some of the modes by which it is known, or presumed, that their dissemination takes place. In this summary we have been compelled to rest content with suggestions, since an exhaustive essay would have occupied considerable space. The variability in the fruit of fungi, in so far as we have failed to demonstrate, will be found exhibited in the illustrated works devoted more especially to the minute species.[F]