Fig. 45.—Spores of (a) Agaricus mucidus; (b) Agaricus vaginatus; (c) Agaricus pascuus; (d) Agaricus nidorosus; (e) Agaricus campestris. (Smith.)

Fig. 46.—Spores of (a) Lactarius blennius; (b) Lactarius fuliginosus; (c) Lactarius quietus. (Smith.)

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.

Fig. 46a.—(a) Spore of Gomphidius viscidus; (b) spore of Coprinus micaceus.

Fig. 47.—Spores of (a) Polyporus cæsius; (b) Boletus parasiticus; (c) Hydnum.

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]

Fig. 48.—Diachea elegans.

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.

Fig. 63.—Spores of Helicocoryne.

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.

Fig. 64.—Sporidium of Genea verrucosa.

Fig. 65.—Alveolate sporidium of Tuber.

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.

Fig. 66.—Asci, sporidia, and paraphyses of Ascobolus (Boudier).

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.

Fig. 67.—Sporidium of Ostreichnion Americanum.

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.

Fig. 78.—Sporidium of Sphæria putaminum. × 400.

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]

[A]

Cunningham, in “Ninth Annual Report of the Sanitary Commissioner with the Government of India.” Calcutta, 1872.

[B]

See “Corda Icones,” tab. 2.

[C]

Corda, “Icones Fungorum,” vol. vi. Prague.

[D]

Tulasne, “Fungi Hypogæi.” Paris.

[E]

Winter, “Die Deutschen Sordarien” (1873).

[F]

Corda, “Icones Fungorum,” 6 vols. (1837–1842); Sturm, “Deutschlands Flora,” Pilze (1841); Tulasne, “Selecta Fungorum Carpologia;” Bischoff, “Kryptogamenkunde” (1860); Corda, “Anleitung zum Studium der Mykologie” (1842); Fresenius, “Beiträge zur Mykologie” (1850); Nees Ton Esenbeck, “Das System der Pilze” (1816); Bonorden, “Handbuch der Allgemeinen Mykologie” (1851).

VII.

GERMINATION AND GROWTH.

In describing the structure of these organisms in a previous chapter, the modes of germination and growth from the spores have been purposely excluded and reserved for the present. It may be assumed that the reader, having followed us to this point, is prepared for our observations by some knowledge of the chief features of structure in the principal groups, and of the main distinctions in the classification, or at least sufficient to obviate any repetition here. In very many species it is by no means difficult to induce germination of the spores, whilst in others success is by no means certain.

M. de Seynes made the Hymenomycetes an especial object of study,[A] but he can give us no information on the germination and growth of the spore. Hitherto almost nothing is positively known. As to the form of the spore, it is always at first spherical, which it retains for a long time, while attached to the basidia, and in some species, but rarely, this form is final, as in Ag. terreus, &c. The most usual form is either ovoid or regularly elliptic. All the Coprini have the spores oval, ovoid, more or less elongated or attenuated from the hilum, which is more translucent than the rest of the spore. This last form is rather general amongst the Leucospores, in Amanita, Lepiota, &c. At other times the spores are fusiform, with regularly attenuated extremities, as in Ag. ermineus, Fr., or with obtuse extremities, as in Ag. rutilans, Sch. In Hygrophorus they are rather irregular, reniform, or compressed in the centre all round. Hoffmann[B] has given a figure taken from Ag. chlorophanus, and Seynes verified it upon Ag. ceraceus, Sow. (See figures on page 121.)

The exospore is sometimes roughened, with more or less projecting warts, as may be seen in Russula, which much resembles Lactarius in this as in some other particulars. The spores of the Dermini and the Hyporhodii often differ much from the sphærical form. In Ag. pluteus, Fr., and Ag. phaiocephalus, Bull, there is already a commencement of the polygonal form, but the angles are much rounded. It is in Ag. sericeus, Ag. rubellus, &c., that the polygonal form becomes most distinct. In Dermini the angles are more or less pronounced, and become rather acute in Ag. murinus, Sow., and Ag. ramosus, Bull. The passage from one to the other may be seen in the stellate form of the conidia of Nyctalis.

It is almost always the external membrane that is coloured, which is subject to as much variation as the form. The more fine and more delicate shades are of rose, yellow-dun or yellow, violet, ashy-grey, clear fawn colour, yellow-orange, olive-green, brick-red, cinnamon-brown, reddish-brown, up to sepia-black and other combinations. It is only by the microscope and transparency that one can make sure of these tints; upon a sufficient quantity of agglomerated spores the colour may be distinguished by the naked eye. Colour, which has only a slight importance when considered in connection with other organs, acquires much in the spores, as a basis of classification.

With the growth of Agarics from the mycelium, or spawn, we are not deficient in information, but what are the conditions necessary to cause the spores themselves to germinate before our eyes and produce this mycelium is but too obscure. In the cultivated species we proceed on the assumption that the spores have passed a period of probation in the intestines of the horse, and by this process have acquired a germinating power, so that when expelled we have only to collect them, and the excrement in which they are concealed, and we shall secure a crop.[C] As to other species, we know that hitherto all attempts to solve the mystery of germination and cultivation has failed. There are several species which it would be most desirable to cultivate if the conditions could be discovered which are essential to germination.[D] In the same manner the Boleti and Hydnei—in fact, all other hymenomycetal fungi, with the exception of the Tremellini—still require to be interrogated by persevering experiment and close inquiry as to their mode of germination, but more especially as to the essential conditions under which alone a fruitful mycelium is produced.

Fig. 79.—(a) Basidia and spores of Exidia spiculosa; (b) Germinating spore.

The germination of the spore has been observed in some of the Tremellini. Tulasne described it in Tremella violacea.[E] These spores are white, unilocular, and filled with a plastic matter of homogeneous appearance. From some portion of their surface an elongated germ filament is produced, into which the contents of the reproductive cell pass until quite exhausted. Other spores, perhaps more abundant, have a very different kind of vegetation. From their convex side, more rarely from the outer edge, these particular spores emit a conical process, generally shorter than themselves, and directed perpendicularly to the axis of their figure. This appendage becomes filled with protoplasm at the expense of the spore, and its free and pointed extremity finally dilated into a sac, at first globose and empty. This afterwards admits into its cavity the plastic matter contained in its support, and, increasing, takes exactly the form of a new spore, without, however, quite equalling in size the primary or mother spore. The spore of the new formation long retains its pedicel, and the mother spore which produced it, but these latter organs are then entirely empty and extremely transparent. Sometimes two secondary spores are thus engendered from the same spore, and their pedicels may be implanted on the same or on different sides, so as to be parallel in the former case, and growing in opposite directions in the latter. The fate of these secondary spores was not determined.

Fig. 80.—Germinating spore and (a) corpuscles of Dacrymyces deliquescens.

In Dacrymyces deliquescens are found mingled amongst the spores immense numbers of small round or ovoid unilocular bodies, without appendages of any kind, which long puzzled mycologists. Tulasne ascertained that they are derived from the spores of this fungus when they have become free, and rest on the surface of the hymenium. Each of the cells of the spore emits exteriorly one or several of these corpuscles, supported on very short slender pedicels, which remain after the corpuscles are detached from them. This latter circumstance evidences that new corpuscles succeed the firstborn one on each pedicel as long as there remains any plastic matter within the spore. The latter, in fact, in consequence of this labour of production, becomes gradually emptied, and yet preserves the generative pedicels of the corpuscles, even when it no longer contains any solid or coloured matter. These pedicels are not all in the same plane, as may be ascertained by turning the spore on its longitudinal axis; but it often seems to be so when they are looked at in profile, on account of the very slight distance which then separates them one from another. It will also be remarked that they are in this case often implanted all on the same side of the reproductive body, and most often on its convex side. Their fecundity is exhausted with the plastic contents of the spore. The corpuscles, when placed in the most favourable conditions, have never given the least sign of vegetation; they have also remained for a long time in water without experiencing any appreciable alteration.

All the individuals of Dacrymyces deliquescens do not produce these corpuscles in the same abundance; those which bear the most are recognizable by the pale tint of the reproductive dust with which they are covered; in others, where this dust preserves its golden appearance, only a few corpuscles are found. The spores which produce corpuscles do not appear at all apt to germinate. On the other hand, multitudes of spores will germinate which had not produced any corpuscles. Tulasne remarks on this, that these observations would authorize us to think that all spores, though perfectly identical to our eyes, have not, without distinction, the same fate, nor doubtless the same nature; and, in the second place, that these two kinds of bodies, if they are not always isolated, yet are most frequently met with on distinct individuals. This author claims for the corpuscles in question that they are spermatia, and thinks that their origin is only so far unusual in that they proceed from veritable spores.

The whole of the Gasteromycetes have as yet to be challenged as to the mode and conditions of germination and development. It is probable that these will not materially differ from those which prevail in Hymenomycetes.

The germination in Æcidium has been followed out by Tulasne,[F] either by placing the pseudospores in a drop of water, or confining them in a moist atmosphere, or by placing the leaves on which the Æcidium flourishes upon water. The pseudospores plunged in water germinated more readily than the others. If the conditions were favourable, germination would take place in a few hours. Æcidium Ranunculacearum, D. C., on leaves of figwort, gives rarely more than one germinating filament, which soon attains three times the length of the diameter of the pseudospore. This filament generally remains simple, sometimes torulose, and distorted in a long spire. Sometimes it has been seen divided into two branches, nearly equal to each other. The spore in germinating empties itself of its plastic contents, contracts, and diminishes in size. The pseudospores of Æcidium crassum, P., emit three long filaments, which describe spirals, imitating the twistings of the stem of a bean or bindweed. In Æcidium Violæ, Schum, one filament is produced, which frequently rolls up its anterior extremity into a spire, but more often this same extremity rises in a large ovoid, irregular vesicle, which continues the axis of the filament, or makes with it a more or less decided angle. In whatever manner placed, this vesicle attracts to it all the orange protoplasm, and hardly does this become settled and complete before the vesicle becomes the starting point of a new development, for it begins to produce at its apex a filament, more slender than the previous one, stiff, and unbranched.

Fig. 81.—Germination of Æcidium Euphorbia (sylvaticæ), Tulasne.

According to M. Tulasne, the germination of the pseudospores of Æcidium Euphorbiæ on Euphorbia sylvatica differ in some respects from the preceding. When dropped upon water these spores very soon emit a short tube, which ordinarily curves in an arch or circle, almost from its origin, attaining a length of from three to six times the diameter of the spore; then this tube gives rise to four spicules, each of which produces a small obovate or reniform sporule; the generation of these sporules absorbs all the plastic matter contained in the germ-tube, which permits of the observation that it was divided into four cells corresponding with the number of spicules. These sporules germinate very rapidly from an indefinite point of their surface, emitting a filiform process, which is flexuous and very delicate, not extending more in length than three times that of the long axis of the sporule, often less, reproducing at its summit a new sporule, differing in form and size from that which preceded it. This sporule of the second formation becomes at its apex a vital centre, and sprouts one or more linear buds, of which the elongation is occasionally interrupted by the formation of vesicular swellings. As Tulasne observes, the pseudospores of the Æcidium and the greater number of Uredines are easily wetted with water before arriving at maturity; but when they are ripe, on the contrary, they appear to be clothed with a greasy matter which protects them from the liquid, forcing them almost all to rest on the surface.

The pseudospores of Rœstelia are produced in strings or chaplets, as in Æcidium, with this difference, that instead of being contiguous they are separated by narrow isthmuses. The ripe pseudospores are enveloped in a thick tegument, of a dark brown colour. They germinate readily on water, producing a filament fifteen times as long as the diameter of the spore. This filament is sometimes rolled or curved. Towards its extremity it exhibits protuberances which resemble the rudiments of ramuli, or they terminate in a vesicle which gives rise to a slender filament. The tegument of these pseudospores, above all in those which have germinated, and have consequently become more transparent, it is easy to see has many pores, or round ostioles.

In Peridermium the pseudospores, when dropped upon water, germinate at any point of their surface. Sometimes two unequal filaments issue from the same spore. After forty-eight hours of vegetation in the air, the greater part had already emitted a multitude of thick little branches, themselves either simple or branched, giving to the filaments a peculiar aspect. Tulasne did not on any occasion observe the formation of secondary spores.

Fig. 82.—Germinating pseudospores of (b) Coleosporium Sonchi; (s s) secondary spores, or sporules (Tulasne).

In the Uredines proper the germination seems to be somewhat similar, or at least not offering sufficient differences to warrant special reference in Uredo, Trichobasis, Lecythea, &c. In Coleosporium there are two kinds of spores, one kind consisting of pulverulent single cells, and the other of elongated septate cells, which break up into obovate joints. Soon after the maturity of the pulverulent spores, each begins to emit a long tube, which is habitually simple, and produces at its summit a reproductive cellule, or reniform sporule. The orange protoplasm passes along the colourless tubes to the terminal sporule at the end of its vegetation. The two forms of spores in this genus are constantly found on the same leaf, and in the same pulvinule, but generally the pulverulent spores abound at the commencement of the summer. The reniform sporules begin to germinate in a great number as soon as they are free; some few extend a filament which remains simple and uniform, but more commonly it forms at its extremity a second sporule. If this does not become isolated, to play an independent life, the filament is continued, and new vesicles are repeated many times.

Fig. 83.—Germinating pseudospore (b) of Melampsora betulina (Tulasne).

In Melampsora the summer spores are of the Lecythea type, and were included in that genus till their relation with Melampsora was clearly made out. The winter spores are in solid pulvinules, and their fructification takes place towards the end of winter or in the spring. This phenomenon consists in the production of cylindrical tubes, which start from the upper extremity of the wedge-shaped spores, or more rarely from the base. These tubes are straight or twisted, simple or bifurcated, and each of them very soon emits four monosporous spicules, at the same time that they become septate. The sporules are in this instance globose.

Fig. 84.—Germinating pseudospore of Uromyce appendiculatus. (Tulasne.)

In Uromyces germination follows precisely the same type as that of the upper cell of Puccinia; in fact, Tulasne states that it is very difficult to say in what they differ from the Pucciniæ which are accidentally unilocular.

In Cystopus a more complex method prevails, which will be examined more closely hereafter.

Fig. 85.—Germinating pseudospore of Puccinia Moliniæ. (Tulasne.)

In Puccinia, as already observed when describing their structure, the pseudospores are two-celled. From the pores of each cell, which are near the central septum, springs a clavate tube, which attains two or three times the total length of the fruit, and of which the very obtuse extremity curves more or less in the manner of a crozier.[G] This tube, making a perfectly uncoloured transparent membrane, is filled with a granular and very pale plastic matter at the expense of the generative cell, which is soon rendered vacant; then it gives rise to four spicules, usually on the same side, and at the summit of these produces a reniform cellule. The four sporules so engendered exhaust all the protoplasm at first contained in the generative cell, so that their united capacity proves to be evidently much insufficient to contain it, the more so as it leads to the belief that this matter undergoes as it condenses an elaboration which diminishes its size. In all cases the spicule originates before the sporule which it carries, and also attains its full length when the sporule appears. The form of the latter is at first globular, then ellipsoid, and more or less curved. All these phases of vegetation are accomplished in less than twelve hours, and if the spore is mature and ready for germination, it is sufficient to provoke it by keeping the pseudospores in a humid atmosphere. During this process the two cells do not separate, nor does one commence germination before the other, but both simultaneously. When the sporules are produced, the protospore, somewhat analogous to a prothallus, has performed its functions and decays. Towards the time of the falling of the sporules they are nearly all divided into four unequal cells by transverse and parallel septa. These sporules in time produce, from any point on their surface, a filament, which reproduces a new sporule, resembling the first, but generally smaller. This sporule of the second generation ordinarily detaches itself from its support before germinating.

Fig. 86.—Germinating pseudospore of Triphragmium ulmariæ (Tulasne.)

The pseudospores of Triphragmium ulmariæ have been seen in April germinating on old leaves of the meadowsweet which survived the winter, whilst at the same time new tufts of the spores were being developed on the leaves of the year. These fruits of the spring vegetation would not germinate the same year. Each cell in germination emits a long cylindrical filament, containing a brownish protoplasm, on which four spicules, bearing as many sporules, are generated.

Fig. 87.—Germinating pseudospore of Phragmidium bulbosum. (Tulasne.)

The germination of the black fruits of Phragmidium only appears to take place in the spring. It greatly resembles that in Puccinia, except that the filament is shorter, and the sporules are spherical and orange-coloured, instead of being kidney-shaped and pale. In the species found on the leaves of the common bramble, the filament emitted by each cell attains three or four times the length of the fruit. The granular orange protoplasm which fills it passes ere long into the sporules, which are engendered at the extremity of pointed spicules. After the long warty fruits are emptied of their contents they still seem as dark as before, but the pores which are pierced in the sides, through which the germinating filaments have proceeded, are more distinctly visible.

It will be observed that throughout all these allied genera of Uromyces, Puccinia, Triphragmium, and Phragmidium the same type of germination prevails, which confirms the accuracy of their classification together, and renders still less probable the supposed affinity of Phragmidium with Sporidesmium, which was at one time held by very astute mycologists, but which is now abandoned. This study of germination leads also to a very definite conclusion with regard to the genus Uromyces—that it is much more closely related to Puccinia and its immediate allies than to other unicellular Uredines.

Fig. 88.—Germinating pseudospores of Podisoma Juniperi. (Tulasne)

The germination of the pseudospores of the gelatinous Uredines of the genus Podisoma was studied by Tulasne.[H] These pretended spores, he writes, are formed of two large conical cells, opposed by their base and easily separating. They vary in length. The membrane of which they are formed is thin and completely colourless in most of them, though much thicker and coloured brown in others. It is principally the spores with thin membranes that emit from near the middle very obtuse tubes, into which by degrees, as they elongate, the contents of the parent utricles pass. Each of the two cells of the supposed spore may originate near its base four of these tubes, opposed to each other at their point of origin, and their subsequent direction; but it is rather rare for eight tubes, two by two, to decussate from the same spore or basidium. Usually there are only two or three which are completely developed, and these tend together towards the surface of the fungus, which they pass, and expand at liberty in the air. The tubes generally become thicker by degrees as they elongate, some only slightly exceeding the length of the protospores. Others attain three or four times that length, according to the greater or less distance between the protospore and the surface of the plant. In the longest tubes it is easy to observe how the colouring matter passes to their outer extremity, leaving the portion nearest to the parent cell colourless and lifeless. When nearly attaining their ultimate dimensions, all the tubes are divided towards their outer extremity by transverse septa into unequal cells; then simple and solitary processes, of variable length and form, but attenuated upwards, proceed from each segment of the initial tube, and produce at their extremity an oval spore (teleutospore, Tul.), which is slightly curved and unilocular. These spores absorb all the orange endochrome from the original tubes. They appear in immense numbers on the surface of the fungus, and when detached from their spicules fall upon the ground or on any object which may be beneath them. So freely are they deposited that they may be collected on paper, or a slip of glass, like a fine gold-coloured powder. Again, these secondary spores (teleutospores) are capable of germination, and many of them will be found to have germinated on the surface of the Podisoma whence they originated. The germ filament which they produce springs habitually from the side, at a short distance from the hilum, which indicates the point of attachment to the original spicule. These filaments will attain to from fifteen to twenty times the diameter of the spore in length before branching, and are in themselves exceedingly delicate. The tubes which issue from the primary spores (protospores, Tul.) are not always simple, but sometimes forked; and the cells which are ultimately formed at their extremities, though producing filiform processes, do not always generate secondary spores (teleutospores) at their apices. This mode of germination, it will be seen, resembles greatly that which takes place in Puccinia.

Fig. 89.—Germinating pseudospore (g) of Tilletia caries with secondary spores in conjugation. (Tul.)

The germination of the Ustilagines was in part examined by Tulasne, but since has received accessions through the labours of Dr. A. Fischer von Waldheim.[I] Nothing, however, of any importance is added to our knowledge of the germination of Tilletia, which was made known as early as 1847.[J] After some days a little obtuse tube is protruded through the epispore, bearing at its apex long fusiform bodies, which are the sporules of the first generation. These conjugate by means of short transverse tubes, after the manner of the threads of Zygnema. Afterwards long elliptical sporules of the second generation are produced on short pedicels by the conjugated fusiform bodies of the first generation. (Fig. 89, ss.) Ultimately these sporules of the second generation germinate, and generate, on short spicules, similar sporules of a third generation. (Fig. 89, st.)

Fig. 90.—Pseudospore of Ustilago receptaculorum in germination, and secondary spores in conjugation. (Tul.)

In Ustilago (flosculorum) germination takes place readily in warm weather. The germ tube is rather smaller at its base than further on. In from fifteen to eighteen hours the contents become coarsely granular; at the same time little projections appear on the tube which are narrowed at the base, into which some of the protoplasm passes. These ultimately mature into sporules. At the same time a terminal sporule generally appears on the threads. Secondary sporules frequently grow from the primary, which are rather smaller, and these occasionally give rise to a third generation.

In Urocystis (pompholygodes) the germinating tubes spring exclusively from the darker central cells of the clusters. From these are developed at their extremity three or four linear bodies, as in Tilletia, but after this no further development has as yet been traced. It may be remarked here that Waldheim observed similar conjugation of the sporules in some species of Ustilago as have been remarked in the sporules of the first generation in Tilletia.

Fig. 91.—Conidia and zoospores of Cystopus candidus; a. conidium with the plasma divided; b. zoospores escaping; c. zoospores escaped from the conidium; d. active zoospores; e. zoospores, having lost their cilia, commencing to germinate.

Returning to Cystopus, as the last of the Uredines, we must briefly recapitulate the observations made by Professor de Bary,[K] who, by the bye, claims for them an affinity with Peronospora (Mucedines but too well known in connection with the potato disease), and not with the Uredines and their allies. In this genus there are two kinds of reproductive organs, those produced on the surface of the plant bursting through the cuticle in white pustules, and which De Bary terms conidia, which are generated in chains, and certain globose bodies termed oogonia, which are developed on the mycelium in the internal tissues of the foster plant. When the conidia are sown on water they rapidly absorb the moisture, and swell; the centre of one of the extremities soon becomes a large obtuse papilla resembling the neck of a bottle. This is filled with a granular protoplasm, in which vacuoles are formed. Soon, however, these vacuoles disappear, and very fine lines of demarcation separate the protoplasm into from five to eight polyhedric portions, each presenting a little faintly-coloured vacuole in the centre (a). Soon after this division the papilla at the extremity swells, opens itself, and at the same time the five to eight bodies which had formed in the interior are expelled one by one (b). These are zoospores, which at first take a lenticular form, and group themselves before the mouth of the parent cell in a globose mass (c.) Very soon, however, they begin to move, and then vibratile cilia show themselves (d), and by means of these appendages the entire globule moves in an oscillating manner as one by one the zoospores disengage themselves, each becoming isolated and swimming freely in the surrounding fluid. The movement is precisely that of the zoospores of Algæ.

Fig. 92.—Resting spore of Cystopus candidus with zoospores escaped.

The generation of the zoospores commences within from an hour and a half to three hours after the sowing of the conidia on water. From the oogonia, or resting spores, similar zoospores, but in greater number, are generated in the same manner, and their conduct after becoming free is identical. Their movements in the water usually last from two to three hours, then they abate, the cilia disappear, and the spore becomes immovable, takes a globose form, and covers itself with a membrane of cellulose. Afterwards the spore emits, from any point whatever of its surface, a thin, straight or flexuous tube, which attains a length of from two to ten times the diameter of the spore. The extremity becomes clavate or swollen, after the manner of a vesicle, which receives by degrees the whole of the protoplasm.

De Bary then proceeds to describe experiments which he had performed by watering growing plants with these zoospores, the result being that the germinating tubes did not penetrate the epidermis, but entered by the stomates, and there put forth an abundant mycelium which traversed the intercellular passages. Altogether the germination of these conidia or zoospores offers so many differences from the ordinary germination of the Uredines, and is so like that which prevails in Peronospora, in addition to the fact of both genera producing winter spores or oogonia, that we cannot feel surprised that the learned mycologist who made these observations should claim for Cystopus an affinity with Peronospora rather than with the plants so long associated with it amongst the Coniomycetes.

In passing from these to the Mucedines, therefore, we cannot do so more naturally than by means of that genus of white moulds to which we have just alluded. The erect branched threads bear at the tip of their branchlets spores, or conidia, which conduct themselves in a like manner to the organs so named in Cystopus, and oogonia or resting spores developed on the mycelium within the tissues of the foster plant also give origin to similar zoospores.

The conidia are borne upon erect, elongated filaments, originating from the creeping mycelium. These threads are hollow, and rarely septate; the upper portion divided into numerous branches, and these again are subdivided, the ultimate ramuli each terminated by a single conidium. This body when mature is oval or elliptical, filled with protoplasm, but there is a diversity in their mode of germination. In the greater part, of which P. effusa may be taken as an example, the conidia have the function of simple spores. Placed in favourable conditions, each of them puts forth a germ-tube, the formation of which does not differ in any essential point from what is known of the spores of the greater part of fungi.

The short oval conidia of P. gangliformis have little obtuse papillæ at their apex, and it is at this point that germination commences.

The conidia of P. densa are similar, but the germination is different. When placed in a drop of water, under favourable circumstances, the following changes may be observed in from four to six hours. The protoplasm, at first uniformly distributed in all the conidia, appears strewn with semi-lenticular, and nearly equidistant vacuoles, of which the plane face is immediately in contact with the periphery of the protoplasm. These vacuoles number from sixteen to eighteen in P. macrocarpa, but are less numerous in P. densa. A short time after the appearance of the vacuoles the entire conidium extends itself so that the papilla disappears. Suddenly it reappears, elongates itself, its attenuated membrane vanishes, and the protoplasm is expelled by the narrow opening that remains in place of the papilla. In normal cases the protoplasm remains united in a single mass that shows a clear but very delicate outline. When it has reached the front of the opening in the conidium, which is thus emptied, the mass remains immovable. In P. densa it is at first of a very irregular form, but assumes by degrees a regular globose shape. This is deprived of a distinct membrane, the vacuoles that disappeared in the expulsion again become visible, but soon disappear for a second time. The globule becomes surrounded with a membrane of cellulose, and soon puts out from the point opposite to the opening of the conidium a thick tube which grows in the same manner as the germ-tube of the conidia in other species. Sometimes the expulsion of the protoplasm is not completely accomplished; a portion of it remaining in the membrane of the conidium detaches itself from the expelled portion, and while this is undergoing changes takes the form of a vesicle, which is destroyed with the membrane. It is very rare that the protoplasm is not evacuated, and that the conidia give out terminal or lateral tubes in the manner that is normal to other species without papillæ. The germination just described does not take place unless the conidia are entirely surrounded by water; it is not sufficient that they repose upon its surface. Besides, there is another condition which, without being indispensable, has a sensible influence on the germination of P. macrocarpa, and that is the exclusion of light. To ascertain if the light or the darkness had any influence, two equal sowings were placed side by side, the one under a clear glass bell, the other under a blackened glass bell. Repeated many times, these experiments always gave the same result—germination in from four to six hours in the conidia under the blackened glass; no change in those under the clear glass up to the evening. In the morning germination was completed.

The conidia of P. umbelliferarum and P. infestans[L] show an analogous structure. These bodies, if their development be normal, become zoosporangia. When they are sown upon water, one sees at the end of some hours the protoplasm divided by very fine lines, and each of the parts furnished with a small central vacuole. Then the papilla of the conidium disappears. In its place appears a rounded opening, by which the parts of the protoplasm are expelled rapidly, one after the other. Each of these, when free, immediately takes the form of a perfect zoospore, and commences to agitate itself. In a few moments the sporangium is empty and the spores disappear from the field of the microscope.

The zoospores are oval or semi-oval, and in P. infestans the two cilia spring from the same point on the inferior border of the vacuole. Their number in a sporangium are from six to sixteen in P. infestans, and from six to fourteen in P. umbelliferarum. The movement of the zoospores ceases at the end of from fifteen to thirty minutes. They become motionless, cover themselves with a membrane of cellulose, and push out slender bent germ-tubes which are rarely branched. It is but seldom that two tubes proceed from the same spore. The same development of the zoospores in P. infestans is favoured by the exclusion of the light. Placed in a position moderately lighted or protected by a blackened bell, the conidia very readily produced zoospores.

A second form of germination of the conidia in P. infestans, when sown upon a humid body or on the surface of a drop of water, consists in the conidium emitting from its summit a simple tube, the extremity of which swells itself into the form of an oval vesicle, drawing to itself, little by little, all the protoplasm contained in the conidium. Then it isolates itself from the germ-tube by a septum, and takes all the essential characteristics of the parent conidium. This secondary conidium can sometimes engender a third cellule by a similar process. These secondary and tertiary productions have equally the character of sporangia. When they are plunged into water, the ordinary production of zoospores takes place.

Lastly, there is a third mode of germination which the conidia of P. infestans manifest, and which consists in the conidium emitting from its summit a simple or branched germ-tube. This grows in a similar manner to the conidia first named as of such species as P. effusa. The conditions which control this form of germination cannot be indicated, since some conidia which germinate after this manner will sometimes be found mixed with others, the majority of which furnish zoospores. It may be that the conidia themselves are in some sort of abnormal condition.

In all the species examined the conidia possess the power of germination from the moment of their maturity. The younger they are the more freely they germinate. They can retain this power for some days or weeks, provided they are not entirely dried. Dessication in an ordinary temperature seemed sufficient to destroy the faculty of germinating in twenty-four hours, when the conidia had been removed from the leaves on which they were produced. They none of them retained the faculty during a few months, hence they cannot preserve it during the winter.

The germs of Peronospora enter the foster plant if the spores are sown upon a part suitable for the development of the parasite. It is easy to convince one’s self that the mycelium, springing from the penetrating germs, soon takes all the characters that are found in the adult state. Besides, when cultivated for some time, conidiiphorous branches can be seen growing, identical with those to which it owes its origin. Such cultivation is so readily accomplished that it can be made upon cut leaves preserved fresh in a moist atmosphere.

In the species of Peronospora that inhabit perennial plants, or annual plants that last through the winter, the mycelium hidden in the tissues of the foster-plant lasts with it. In the spring it recommences vegetation, and emits its branches into the newly-formed organs of its host, there to fructify. The Peronospora of the potato is thus perennial by means of its mycelium contained in the browned tissue of the diseased tubers. When in the spring a diseased potato begins to grow, the mycelium rises in the stalk, and soon betrays itself by blackish spots. The parasites can fructify abundantly on these little stalks, and in consequence propagate themselves in the new season by the conidia coming from the vivacious mycelium.

The diseased tubers of the potato always contain the mycelium of P. infestans, which never fructifies there as long as the skin of the tuber is intact. But when, in cutting the tuber, the parenchyma occupied by the mycelium is exposed to the contact of the air, it covers itself with conidia-bearing branches at the end of from twenty-four to forty-eight hours. Analogous results are obtained with the stalks of the potato. It is evident that in these experiments nothing is changed except the contact of the air; the specific conditions particularly remain the same. It appears, therefore, that it is this contact alone which determines generally the production of the conidiiferous branches.[M]

The mode of germination and development in the Mucors has been studied by several observers, but most recently by Van Tieghem and Le Monnier.[N] In one of the common forms, the Mucor phycomyces of some authors, and the Phycomyces nitens of others, the process is given in detail. In this species germination will not take place in ordinary water, but it readily takes place in orange juice and other media. The spore loses colour, swells, and absorbs fluid around it until double its original size and ovoid. Then a thick thread is emitted from one or both extremities, which elongates and becomes branched in a pinnate manner. Sometimes the exospore is ruptured and detached loosely from the germinating spore. After about forty-eight hours from the first sowing, the mycelium will send branches into the air, which again become abundantly branched; other short submerged branches will also remain simple, or have tuft-like ramifications, each terminating in a point, so as to bristle with spiny hairs. In two or three days abruptly swollen branches, of a club shape, will make their appearance on the threads both in the air and in the fluid. Sometimes these branches are prolonged into an equal number of sporangia-bearing threads, but most frequently they divide first at their swollen summits into numerous branches, of which usually one, sometimes two or three, develop into sporangia-bearing threads, while the rest are short, pointed, and form a tuft of rootlets. Sometimes these rootlets reduce themselves to one or more rounded protuberances towards the base of the sporangia-bearing threads.

Fig. 93.—Zygospores of Mucor phycomyces. (Van Tieghem.)

There are often also a certain number of the branches which had acquired a clavate shape, and do not erect themselves above the surface, instead of producing a fertile thread, which would seem to have been their first intention, become abruptly attenuated, and are merely prolonged into a mycelial filament. Although in other species chlamydospores are formed in such places on the mycelium, nothing of the kind has been traced in this species, more than here indicated. Occasionally, when germination is arrested prematurely, certain portions of the hyphæ, in which the protoplasm maintains its vitality, become partitioned off. This may be interpreted as a tendency towards the formation of chlamydospores, but there is no condensation of protoplasm, or investiture with a special membrane. Later on this isolated protoplasm is gradually altered, separating into somewhat regular ovoid or fusiform granules, which have, to a certain extent, the appearance of spores in an ascus, but they seem to be incapable of germination.

Another method of reproduction, not uncommon in Mucorini, is described by Van Tieghem in this species. Conjugating threads on the substratum by degrees elaborate zygospores, but these, contrary to the mode in other species, are surrounded by curious branched processes which emanate from the arcuate cells on either side of the newly-developed zygospore. This system of reproduction is again noticed more in detail in the chapter on polymorphism.

M. de Seynes has given the details of his examination of the sporidia of Morchella esculenta during germination.[O] A number of these sporidia, placed in water in the morning, presented, at nine o’clock of the same evening, a sprout from one of the extremities, measuring half the length of the spore. In the morning of the next day this sprout had augmented, and become a filament three or four times as long. The next day these elongated filaments exhibited some transverse divisions and some ramifications. On the third day, the germination being more advanced, many more of the sporidia were as completely changed, and presented, in consequence of the elongation, the appearance of a cylindrical ruffle, the cellular prolongations arising from the germination having a tendency towards one of the extremities of the longer axis of the sporidium, and more often to the two opposed extremities, either simultaneously or successively. Out of many hundreds of sporidia examined during germination, he had only seen a very few exceptions to this rule, among which he had encountered the centrifugal tendency to vegetate by two opposed filaments, proving that if it bears a second by the side of the primal filament situated at one of the poles, a second would also be seen from the side of the filament coming from the opposite pole.

Before being submitted to the action of water, the contents of the sporidia seemed formed of two distinct parts, one big drop of yellow oil of the same form as the sporidium, with the space between it and the cell wall occupied by a clear liquid, more fluid and less refractive, nearly colourless, or at times slightly roseate. As the membrane absorbed the water by which it was surrounded, the quantity of this clear liquid was augmented, and the rosy tint could be more easily distinguished. All the contents of the spore, which up to this time remained divided into two parts, presented altogether one aspect, only containing numerous granulations, nearly of equal size, completely filling it, and reaching the inner face of the sporic membrane.

After this time the sporidium augments in size very rapidly, becoming at times irregular, and sometimes even as much as from two to three times its original dimensions, then there appears at the surface, usually at one of the poles of the ellipse, a small prominence, with an extremely fine membrane, which does not appear to separate itself from that which surrounds the sporidium, and it is difficult to say whether it is a prolongation of the internal membrane going across the outside, or simply a prolongation caused by a continuation of tissue of an unique membrane. Sometimes there may be seen at the point where the primal filament issues from the sporidium a circular mark, which appears to indicate the rupture of the external membrane. From this time another change comes over the contents. We again find the yellow oily liquid, now occupying the external position, with some drops of colourless or roseate liquid in the centre, so that the oily liquid and the more limpid fluid interchange the positions which they occupied previous to the commencement of germination. Whether these two fluids have undergone any change in their constitution is difficult to determine, at all events the oily liquid appears to be less refractive and more granular, and it may be that it is a product of new formation, containing some of the elements of the primitive oily drop. Having regard to the delicate character of the membrane of the germinating filaments, De Seynes supposed that it might offer greater facility for the entrance of water by endosmose, and account for the rapid enlargement of the sporidia. By a series of experiments he became satisfied that this was the case to a considerable extent, but he adds:—“I cannot help supposing that a greater absorption of greasy matter in the cell which is the first product of germination raises an objection to an aqueous endosmose. One can also see in this experience a proof of the existence of two special membranes, and so suppose that the germinative cell is the continuation of the internal membrane, the external membrane alone being susceptible of absorbing the liquids, at least with a certain rapidity.”

Fig. 94.—Sporidium of Ascobolus germinating.

In other Discomycetes germination takes place in a similar manner. Boudier[P] narrates that in Ascobolus, when once the spore reaches a favourable place, if the circumstances are good, i.e., if the temperature is sufficiently high and the moisture sufficient, it will germinate. The time necessary for this purpose is variable, some hours sufficing for some species; those of A. viridis, for example, germinate in eight or ten hours, doubtless because, being terrestrial, it has in consequence less heat. The spore slightly augments in size, then opens, generally at one or other extremity, sometimes at two, or at any point on its surface, in order to pass the mycelium tubes. At first simple, without septa, and granular in the interior, above all at the extremity, these tubes, the rudiment of the mycelium, are not long in elongating, in branching, and later in having partitions. These filaments are always colourless, only the spore may be coloured, or not. Coemans has described them as giving rise to two kinds of conidia,[Q] the one having the form of Torula, when they give rise to continuous filaments, the other in the form of Penicillium, when they give birth to partitioned filaments. De Seynes could never obtain this result. Many times he had seen the Penicillium glaucum invade his sowings, but he feels confident that it had nothing to do with the Ascobolus. M. Woronin[R] has detailed some observations on the sexual phenomena which he has observed in Ascobolus and Peziza, and so far as the scolecite is concerned these have been confirmed by M. Boudier.

There is no reason for doubt that in other of the Discomycetes the germination of the sporidia is very similar to that already seen and described, whilst in the Pyrenomycetes, as far as we are aware, although the production of germinating tubes is by no means difficult, development has not been traced beyond this stage.[S]

[A]

Seynes, J. de, “Essai d’une Flore Mycologique de la Montpellier,” &c. (1863), p. 30.

[B]

Hoffman, “Icones Analyticæ Fungorum.”

[C]

The spores of Agarics which are devoured by flies, however, though returned in their dung in an apparently perfect state, are quite effete. It is, we believe, principally by the Syrphidæ, which devour pollen, that fungus spores are consumed.

[D]

All attempts at Chiswick failed with some of the more esculent species, and Mr. Ingram at Belvoir, and the late Mr. Henderson at Milton, were unsuccessful with native and imported spawn.

[E]

Tulasne, “On the Organization of the Tremellini,” “Ann. des. Sci. Nat.” 3^me sér. xix. (1853), p. 193.

[F]

Tulasne, “Mémoire sur les Urédinées.”

[G]

Tulasne, in his “Memoirs on the Uredines.”

[H]

Mr. Berkeley has lately published a species under the name of P. Ellisii, in which the gelatinous element is scarcely discernible till the plant is moistened. There are two septa in this species, and another species or form has lately been received from Mr. Ellis which has much shorter pedicels, and resembles more closely Puccinia, from which it is chiefly distinguished by its revivescent character.

[I]

Von Waldheim, on the “Development of the Ustilagineæ,” in “Pringsheim’s Jahrbucher,” vol. vii. (1869); translated in “Transactions of N. Y. State Agricultural Society for 1870.”

[J]

Berkeley, on the “Propagation of Bunt,” in “Trans. Hort. Soc. London,” ii. (1847), p. 113; Tulasne, second memoir, in “Ann. des. Sci. Nat.” ii. (4^me sér.), p. 77; Cooke, in “Journ. Quekett Micro. Club,” i. p. 170.

[K]

De Bary, “Recherches,” &c. in “Annales des Sciences Naturelles” (4^me sér.), xx. p. 5; Cooke in “Pop. Sci. Rev.” iii. (1864), p. 459.

[L]

This is the mould which produces the potato murrain.

[M]

De Bary, “Champignons parasitiques,” in “Annales des Sci. Nat.” (4^me sér.), xx. p. 5; Cooke, “Microscopic Fungi,” cap. xi. p. 138; “Popular Science Review,” iii. 193 (1864).

[N]

Van Tieghem and Le Monnier, “Researches on Mucorini,” in “Ann. des Sci. Nat.” (1873), xvii. p. 261; Summary in “Quart. Journ. Micro. Science” (2nd ser.), xiv. p. 49.

[O]

Seynes, “Essai d’une Flore Mycologique.”

[P]

Boudier, “Mémoire sur l’Ascoboles,” pt. i. iv. f. 13–15.

[Q]

Coemans, “Spicilége Mycologique,” i. p. 6.

[R]

Woronin, “Abhandlungen der Senchenbergischen Naturfor. Gesellschaft” (1865), p. 333.

[S]

In the very important observations made by Dr. Cunningham at Calcutta, on substances floating in the atmosphere, it appeared that the sporidia of many Sphæriæ actually germinated after being taken up by the air. The multitude of fungus spores which were observed in every case was quite extraordinary.

VIII.

SEXUAL REPRODUCTION.

The existence of some sort of sexual reproduction in Fungi has long been suspected, although in earlier instances upon insufficient grounds; but of late years observations have multiplied and facts accumulated which leave no doubt of its existence. If the Saprolegniæ are left out of the question as disputed Fungi, there still remain a number of well authenticated instances of the phenomena of copulation, and many other facts which indicate some sort of sexual relationship. The precise manner in which those minute bodies, so common amongst the Sphæronemei, which we prefer to call stylospores, perform their functions is still to a great extent a mystery; yet it is no longer doubted that certain species of Aposphæria, Phoma, Septoria, &c., are only conditions of some species of Sphæria, often developed and matured in close proximity to them on the same host. In Æcidium, Rœstelia, &c., spermogonia are produced plentifully on or near the same spots on which the fructification appears, either simultaneously or at a later period.[A] The relation of Cytispora to Valsa was suspected by Fries very many years ago, and, as since demonstrated, with very good reason. All attempts, however, to establish anything like sexual reproduction in the higher forms of Hymenomycetes have at present been unsuccessful; and the same may be said of the Gasteromycetes; but in Ascomycetes and Physomycetes instances abound.

We know not whether any importance is to be attached to the views of M. A. S. Œrsted,[B] which have not since been confirmed, but which have been cited with some approval by Professor de Bary, as to a trace of sexual organs in Hymenomycetes. He is supposed to have seen in Agaricus variabilis, P., oocysts or elongated reniform cells, which spring up like rudimentary branches of the filaments of the mycelium, and enclose an abundant protoplasm, if not even a nucleus. At the base of these oocysts appear the presumed antheridia, that is to say, one or two slender filaments, which generally turn their extremities towards the oocysts, and which more rarely are applied to them. Then, without ulteriorily undergoing any appreciable modifications, the fertile cell or oocyst becomes enveloped in a network of filaments of mycelium which proceed from the one which bears it, and this tissue forms the rudiments of the cap. The reality of some kind of fecundation in this circumstance, and the mode of the phenomena, if there is one, are for the present equally uncertain. If M. Œrsted’s opinion is confirmed, naturally the whole of the cap will be the product of fecundation. Probably Karsten (Bonplandia, 1862, p. 62) saw something similar in Agaricus campestris, but his account is obscure.

Fig. 95.—Zygospore of Mucor phycomyces.

In Phycomyces the organs of reproduction have been subjected to close examination by Van Tieghem,[C] and although he failed to discover chlamydospores in this, he describes them in other Mucors. In this species, besides the regular sexual development, by means of sporangia, there is a so-called sexual reproduction by means of zygospores, which takes place in this wise. The threads which conjugate to form the zygospores are slender and erect on the surface of the substratum. Two of these threads come into close contact through a considerable length, and clasp each other by alternate protuberances and depressions. Some of the protuberances are prolonged into slender tubes. At the same time the free extremities of the threads dilate, and arch over one towards the other until their tops touch like a vice, each limb of which rapidly increases in size. Each of these arcuate, clavate cells has now a portion of its extremity isolated by a partition, by means of which a new hemispherical cell is formed at the end of each thread at its point of junction with the opposed thread. These cells become afterwards cylindrical by pressure, the protoplasm is aggregated into a mass, the double membrane at the point of first contact is absorbed, and the two confluent masses of protoplasm form a zygospore invested with a tubercular coat and enveloped by the primary wall of the two conjugating cells. During this formation of the zygospore, the two arched cells whence the zygospore originated develop a series of dichotomous processes in close proximity to the walls which separate them from the zygospore. These processes appear at first on one of the arcuate cells in successive order. The first makes its appearance above upon the convex side; the succeeding ones to the right and left in descending order; the last is in the concavity beneath. It is only after the development of this that the first process appears on the opposite cell, which is followed by others in the same order. These dichotomous processes are nothing more than branches developed from the arcuate, or mother cells. During all these changes, while the zygospore enlarges, the wall of the arcuate cells becomes coloured brown. This colouring is more marked on the convex side, and it shows itself first in the cell on which the dichotomous branches are first produced, and which retains the darker tint longer than the other. The zone from whence the processes issue, and also the processes themselves, have their walls blackened deeply, while the walls of the conjugated cells, which continue to clothe the zygospore during the whole of its development, are bluish-black. By pressure, the thin brittle coat which envelopes the zygospore is ruptured, and the coat of the zygospore exposed, formed of a thick cartilaginous membrane, studded with large irregular warts.

The germination of the zygospores in this species has not as yet been observed, but it is probably the same or very similar to that observed in other species of Mucor. In these the rough tuberculate epispore splits on one side, and its internal coat elongates itself and protrudes as a tube filled with protoplasm and oil globules, terminating in an ordinary sporangium. Usually the amount of nutriment contained in the zygospore is exhausted by the formation of the terminal sporangium, according to Brefeld;[D] but Van Tieghem and Le Monnier remark that in their examinations they have often seen a partition formed at about a third of the length of the principal filament from the base, below which a strong branch is given off, and this is also terminated by a large sporangium.

Fig. 96.—Zygospore of Rhizopus in different stages. (De Bary.)

De Bary has given a precise account of the formation of the zygospore in another of the Mucors, Rhizopus nigricans, in which he says that the filaments which conjugate are solid rampant tubes, which are branched without order and confusedly intermingled. Where two of these filaments meet each of them pushes towards the other an appendage which is at first cylindrical and of the same diameter. From the first these two processes are applied firmly one to the other by their extremities; they increase in size, become clavate, and constitute together a fusiform body placed across the two conjugated filaments. Between the two halves of this body there exists no constant difference of size; often they are both perfectly equal. In each there is collected an abundance of protoplasm, and when they have attained a certain development the largest extremity of each is isolated by a septum from the clavule, which thus becomes the support or suspender of the copulative cell. The two conjugated cells of the fusiform body are generally unequal; the one is a cylinder as long as it is broad, the other is disciform, and its length is only equal to half its breadth. The primitive membrane of the clavule forms between the copulative cells a solid partition of two membranes, but soon after the cells have become defined the medial partition becomes pierced in the centre, and then soon entirely disappears, so that the two twin cells are confounded in one single zygospore, which is due to the union of two more or less similar utricles. After its formation the zygospore still increases considerably in size, and acquires a diameter of more than one-fifth of a millimetre. Its form is generally spherical, and flattened on the faces which are united to the suspenders, or it resembles a slightly elongated cask. The membrane thickens considerably, and consists at the time of maturity of two superposed integuments; the exterior or epispore is solid, of a dark blackish-blue colour, smooth on the plane faces in contact with the suspenders, but covered everywhere else with thick warts, which are hollow beneath. The endospore is thick and composed of several layers, colourless, and covered with warts, which correspond and fit into those of the epispore. The contents of the zygospore are a coarsely granular protoplasm, in which float large oleaginous drops. While the zygospore is increasing in size, the suspender of the smaller copulative cell becomes a rounded and stipitate utricle, often divided at the base by a septum, and which attains almost to the size of the zygospore. The suspender of the larger copulative cell preserves its primitive form and becomes scarcely any larger. It is rare that there is not a considerable difference of size between the two conjugated cells and the suspenders.[E]

Similar conjugation with like results also takes place in Syzygites megalocarpus. In this species the germination of the zygospores has been observed. If, after a certain time of repose, these bodies are placed on a moist substratum, they emit a germ-like tube, which, without originating a proper mycelium, develops at the expense of the nutritive material stored in the zygospore into a carpophore or fruit bearer, which is many times dichotomously branched, bearing terminal sporangia characteristic of the species.

It has already been remarked by us that the Saprolegnei are claimed by some authors as Algæ, whilst we are more disposed to regard them as closely allied to the Mucors, and as they exhibit in themselves strong evidence in support of the existence of sexual reproduction, we cannot forbear giving a summary of what has been observed by De Bary and others in this very interesting and singular group of plants, to which M. Cornu has recently dedicated an exhaustive monograph.[F]

In Saprolegnia monoica, and others, the female organs consist of oogonia—that is to say, of cells which are at first globose and rich in plastic matter, which most generally terminate short branches of the mycelium, and which are rarely seen in an interstitial position. The constitutive membrane of the adult oogonia is reabsorbed in a great many points, and is there pierced with rounded holes. At the same time the plasma is divided into a larger or smaller number of distinct portions, which are rounded into little spheres, and separate from the walls of the conceptacle in order to group themselves at the centre, where they float in a watery fluid. These gonospheres are then smooth and bare, with no membrane on their surface of the nature of cellulose.

Fig. 97.—Conjugation in Achlya racemosa. (Cornu.)

During the formation of the oogonia there arise from its pedicel or from neighbouring filaments slight cylindrical curved branches, sometimes turned round the support of the oogonia, and which all tend towards this organ. Their superior extremity is intimately applied to its wall, then ceases to be elongated, becomes slightly inflated, and is limited below by a partition; it is then an oblong cell, slightly curved, filled with protoplasm, and intimately applied to the oogonia—in fact, an antheridium or organ of the male sex. Each oogonium possesses one or several antheridia. Towards the time when the gonospheres are formed it may be observed that each antheridium sends to the interior of the oogonia one or several tubular processes, which have crossed its side wall, and which open at their extremity in order to discharge their contents. These, while they are flowing out, present some very agile corpuscles, and which, considering their resemblance to those in Vaucheria, to which the name of spermatozoids are applied, ought to be considered as the fecundating corpuscles. After the evacuation of the antheridia the gonospheres are found to be covered with cellulose; they then constitute so many oospores, with solid walls. De Bary considers that, bearing in mind analogous phenomena observed in Vaucheria, and the direct observations of Pringsheim,[G] the cellulose membrane on the surface of the gonospheres is only the consequence of a sexual fecundation.

In Achlya dioica the antheridium is cylindrical, the plasma which it encloses is divided into particles, which attain nearly the size of the zoospores of the same plant. These particles become globose cells, grouped in the centre of the antheridium. Afterwards the contents of these latter cells become divided into numerous bacillary spermatozoids, which first break the wall of their mother cell, and then issue from the antheridium. These rod-like corpuscles, which resemble the spermatozoids in Vaucheria, have their movements assisted by a long cilium. It is presumable that here, as in the Algæ, the spermatozoids introduce themselves into the cavity of the oogonium, and unite with the gonospheres.

Amongst obscure and doubtful bodies are those described by Pringsheim, which have their origin in thick filaments or tubes, similar to those which form the zoosporangia, and represent so many distinct little masses of plasma within an homogeneous parietal ganglion. The contour of these plastic masses is soon delineated in a more precise manner. We see in their interior some homogeneous granules, which are at first globose, then oval, and finally travel to the enlarged and ampullæform extremity of the generating tube. There they become rounded or oval cells covered with cellulose, and emit from their surface one or several cylindrical processes, which elongate towards the wall of the conceptacle, and pierce it, without, however, ever projecting very far beyond it. At the same time the lacunose protoplasm of each cell becomes divided into a number of corpuscles, which escape by the open extremity of the cylindrical neck. They resemble in their organization and agility the spermatozoids of Achlya dioica. They soon become motionless in water, and do not germinate. During the development of these organs, the protoplasm of the utricle which contains them offers at first completely normal characteristics, and disappears entirely by degrees as they increase. De Bary and Pringsheim believe that these organs constitute the antheridia of the species of Saprolegnia to which they belong.

The oospores of the Saprolegniæ, when arrived at maturity, possess a tolerably thick double integument, consisting of an epispore and an endospore. After a considerable time of repose they give rise to tubular or vesicular germs, which, without being much elongated, produce zoospores.[H]

De Bary has claimed for the oogonia in Cystopus and Peronospora a kind of fecundation which deserves mention here.[I] These same fruits, he says, which owe their origin to sexual organs, should bear the names of oogonia and antheridia, according to the terminology proposed by Pringsheim for analogous organs in the Algæ. The formation of the oogonia, or female organs, commences by the terminal or interstitial swelling of the tubes of the mycelium, which increase and take the form of large spherical or oboval cells, and which separate themselves by septa from the tube which carries them. Their membrane encloses granules of opaque protoplasm, mingled with numerous bulky granules of colourless fatty matter.

Fig. 98.—Conjugation in Peronospora; a. antheridium. (De Bary.)

The branches of the mycelium which do not bear oogonia apply their obtuse extremities against the growing oogonia; this extremity swells, and, by a transverse partition, separates itself from the supporting tube. It is the antheridium, or male organ, which is formed by this process; it takes the form of an obliquely clavate or obovate cellule, which is always considerably smaller than the oogonium, and adheres to its walls by a plane or convex area. The slightly thickened membrane of the antheridia encloses protoplasm which is finely granular. It is seldom that more than one antheridium applies itself to an oogonium.

The two organs having together achieved their development, the large granules contained in the oogonium accumulate at its centre to group themselves under the form of an irregular globule deprived of a proper membrane, and surrounded by a bed of almost homogeneous protoplasm. This globule is the gonosphere, or reproductive sphere, which, through the means of fecundation, should become the reproductive body, vegetable egg, or oospore. The gonosphere having been formed, the antheridium shoots out from the centre of its face, close against the oogonium, a straight tube, which perforates the walls of the female cell, and traversing the protoplasm of its periphery, directs itself to the gonosphere. It ceases to elongate itself as soon as it touches it, and the gonosphere becomes clothed with a membrane of cellulose, and takes a regular spheroidal form.

Fig. 99.—Antheridia and oogonium of Peronospora. (De Bary.)

Considering the great resemblance of these organs with the sexual organs of the Saprolegniæ, which are closely allied to the Algæ, and of which the sexuality has been proved, De Bary adds, we have no doubt whatever that the phenomena just described represent an act of fecundation, and that the tube pushed out by the antheridium should be regarded as a fecundating tube. It is remarkable that amongst these fungi the tube projected by the antheridium effects fecundation only by contact. Its extremity never opens, and we never find antherozoids; on the contrary, the antheridium presents, up to the maturity of the oospore, the appearance which it presented at the moment of fecundation.

The primitive membrane of the oospore, at first very thin, soon acquires a more sensible thickness, and becomes surrounded by an external layer (epospore), which is formed at the expense of the protoplasm of the periphery. This disappears in proportion as the epispore attains maturity, and finally there only remains a quantity of granules, suspended in a transparent watery fluid. At the period of maturity, the epispore is a slightly thickened, resistant membrane, of a yellowish-brown colour, and finely punctate. The surface is almost always provided with brownish warts, which are large and obtuse, sometimes isolated, and sometimes confluent, forming irregular crests. These warts are composed of cellulose, which reagents colour of a deep blue, whilst the membrane which bears them preserves its primitive colour. One of the warts, larger than the rest, and recognizable by its cylindrical form, always forms a kind of thick sheath around the fecundating tube. The ripe endospore is a thick, smooth, colourless membrane, composed of cellulose containing a bed of finely granulated protoplasm, which surrounds a great central vacuole. This oospore, or resting spore, may remain dormant in this state within the tissues of the foster plant for some months. Its ultimate development by production of zoospores is similar to the production of zoospores from conidia, which it is unnecessary to repeat here. The oospore becomes an oosporangium, and from it at least a hundred germinating bodies are at length expelled.

Amongst the principal observers of certain phenomena of copulation in cells formed in the earliest stages of the Discomycetes are Professor de Bary,[J] Dr. Woronin,[K] and Messrs. Tulasne.[L] In the Ascobolus pulcherrimus of Crouan, Woronin ascertained that the cup derives its origin from a short and flexible tube, thicker than the other branches of the mycelium, and which is soon divided by transverse septa into a series of cells, the successive increase of which finally gives to the whole a torulose and unequal appearance. The body thus formed he calls a “vermiform body.” The same observer also seems to have convinced himself that there exists always in proximity to this body certain filaments, the short arched or inflected branches of which, like so many antheridia, rest their anterior extremities on the utriform cells. This contact seems to communicate to the vermiform body a special vital energy, which is immediately directed towards the production of a somewhat filamentous tissue, on which the hymenium is at a later period developed. This “vermiform body” of M. Woronin has since come to be recognized under the name of “scolecite.”

Tulasne observes that this “scolecite” or ringed body can be readily isolated in Ascobolus furfuraceus. When the young receptacles are still spherical and white, and have not attained a diameter exceeding the one-twentieth of a millimetre, it is sufficient to compress them slightly in order to rupture them at the summit and expel the “scolecite.” This occupies the centre of the little sphere, and is formed of from six to eight cells, curved in the shape of a comma.

In Peziza melanoloma, A. and S., the same observer succeeded still better in his searches after the scolecite, which he remarks is in this species most certainly a lateral branch of the filaments of the mycelium. This branch is isolated, simple, or forked at a short distance from its base, and in diameter generally exceeding that of the filament which bears it. This branch is soon arcuate or bent, and often elongated in describing a spiral, the irregular turns of which are lax or compressed. At the same time its interior, at first continuous, becomes divided by transverse septa into eight or ten or more cells. Sometimes this special branch terminates in a crozier shape, which is involved in the bent part of another crozier which terminates a neighbouring filament. In other cases the growing branch is connected, by its extremity, with that of a hooked branch. These contacts, however, did not appear to Tulasne to be so much normal as accidental. But of the importance of the ringed body, or “scolecite,” there was no room for doubt, as being the certain and habitual rudiment of the fertile cup. In fact, inferior cells are produced from the flexuous filaments which creep about its surface, cover and surround it on all sides, while joining themselves to each other. At first continuous, then septate, these cells by their union constitute a cellular tissue, which increases little by little until the scolecite is so closely enveloped that only its superior extremity can be seen. These cellular masses attain a considerable volume before the hymenium begins to show itself in a depression of their summit. So long as their smallness permits of their being seen in the field of the microscope, it can be determined that they adhere to a single filament of the mycelium by the base of the scolecite which remains naked.

Fig. 100.—Conjugation in Peziza omphalodes. (Tulasne.)

Although Tulasne could not satisfy himself of the presence of any act of copulation in Ascobolus furfuraceus, or Peziza melanoloma, he was more successful with Peziza omphalodes. As early as 1860 he recognized the large globose, sessile, and grouped vesicles which originate the fertile tissue, but did not comprehend the part which these macrocysts were to perform. Each of these emits from its summit a cylindrical tube, generally flexuous, but always more or less bent in a crozier shape, sometimes attenuated at the extremity. Thus provided, these utricles resemble so many tun-shaped, narrow-necked retorts, filled with a granular thick roseate protoplasm. In the middle of these, and from the same filaments, are generated elongated clavate cells, with paler contents, more vacuoles, which Tulasne names paracysts. These, though produced after the macrocysts, finally exceed them in height, and seem to carry their summit so as to meet the crozier-like prolongations. It would be difficult to determine to which of these two orders of cells belongs the initiative of conjugation. Sometimes the advance seems to be on one side, and sometimes on the other. However this may be, the meeting of the extremity of the connecting tube with the summit of the neighbouring paracyst is a constant fact, observed over and over again a hundred times. There is no real junction between the dissimilar cells above described, except at the very limited point where they meet, and there a circular perforation may be discerned at the end, defined by a round swelling, which is either barely visible or sometimes very decided. Everywhere else the two organs may be contiguous, or more or less near together, but they are free from any adherence whatever. If the plastic matters contained in the conjugated cells influence one another reciprocally, no notable modification in their appearance results at first. The large appendiculate cell seems, however, to yield to its consort a portion of the plasma it contains. One thing only can be affirmed from these phenomena, that the conjugated cells, especially the larger, wither and empty themselves, while the upright compressed filaments, which will ultimately constitute the asci, increase and multiply.[M]

Fig. 100a.—Formation of conceptacle in Erysiphe

Certain phenomena concerned in the development of the Erysiphei belong also to this connection. The mycelium of Erysiphe cichoracearum, like that of other species, consists of branched filaments, crossed in all directions, which adhere as they climb to the epidermis of the plant on which the fungus lives as a parasite. The perithecia are engendered where two filaments cross each other. These swell slightly at this point, and each emits a process which imitates a nascent branch, and remains upright on the surface of the epidermis. The process originating from the inferior filament soon acquires an oval form and a diameter double that of the filament; then it becomes isolated from it by a septum, and constitutes a distinct cell, which De Bary[N] terms an oocyst. The appendage which proceeds from the inferior filament always adheres intimately to this cell, and elongates into a slender cylindrical tube, which terminates in an obtuse manner at the summit of the same cell. At its base it is also limited by a septum, and soon after another appears a little below its extremity at a point indicated beforehand by a constriction. This new septum defines a terminal short obtuse cell, the antheridium, which is thus borne on a narrow tube like a sort of pedicel. Immediately after the formation of the antheridia new productions show themselves, both around the oocyst and within it. Underneath this cell eight or ten tubes are seen to spring from the filament which bears it; these join themselves by the sides to each other and to the pedicel of the antheridium, while they apply their inner face to the oocyst, above which their extremities soon meet. Each of the tubes is then divided by transverse septa into two or three distinct cells, and in this manner the cellular walls of the perithecia come into existence.

During this time the oocyst enlarges and divides, without its being possible precisely to determine the way in which it happens, into a central cell and an outer layer, ordinarily simple, of smaller cells, contiguous to the general enveloping wall. The central cell becomes the single ascus, which is characteristic of the species, and the layer which surrounds it constitutes the inner wall of its perithecium. The only changes afterwards observed are the increase in size of the perithecium, the production of the root-like filaments which proceed from its outer wall, the brown tint which it assumes, and finally the formation of the sporidia in the ascus. The antheridium remains for a long time recognizable without undergoing any essential modification, but the dark colour of the perithecium soon hides it from the observer’s eye. De Bary thinks that he is authorized in assuming the probability that the conceptacles and organs of fructification of others of the Ascomycetes, including the Discomycetes and the Tuberacei, are the results of sexual generation.

Certain phenomena which have been observed amongst the Coniomycetes are cited as examples of sexual association. Amongst these may be named the conjugation of the slender spores of the first generation, produced on the germinating threads of Tilletia,[O] and similar acts of conjugation, as observed in some species of Ustilago. Whether this interpretation should be placed on those phenomena in the present condition of our knowledge is perhaps an open question.

Fig. 101.—Tilletia caries with conjugating cells.

Finally, the spermogonia must be regarded as in some occult manner, which as yet has baffled detection, influencing the perfection of sporidia[P] In Rhytisma, found on the leaves of maple and willow, black pitchy spots at first appear, which contain within them a golden pulp, in which very slender corpuscles are mixed with an abundant mucilage. These corpuscles are the spermatia, which in Rhytisma acerinum are linear and short, in Rhytisma salicinum globose. When the spermatia are expelled, the stroma thickens for the production of asci and sporidia, which are afterwards developed during the autumn and winter.

Several of the species of Hysterium also possess spermogonia, notably H. Fraxini, which may be distinguished from the ascigerous perithecia with which they are associated by their smaller size and flask-like shape. From these the spermatia are expelled long before the maturity of the spores. In Hypoderma virgultorum, H. commune, and H. scirpinum, the spermogonia are small depressed black capsules, which contain an abundance of minute spermatia. These were formerly regarded as distinct species, under the name of Leptostroma. In Stictis ocellata a great number of the tubercles do not pass into the perfect state until after they have produced either linear, very short spermatia, or stylospores, the latter being reproductive bodies of an oblong shape, equal in size to the perfect sporidia. Some of the tubercles never pass beyond this stage.

Again, there is a very common fungus which forms black discoid spots on dead holly leaves, called Ceuthospora phacidioides, figured by Greville in his “Scottish Cryptogamic Flora,” which expels a profusion of minute stylospores; but later in the season, instead of these, we find the asci and sporidia of Phacidium ilicis, so that the two are forms and conditions the one of the other.

In Tympanis conspersa the spermogonia are much more commonly met with than the complete fruit. There is a great external resemblance in them to the ascigerous cups, but there is no evidence that they are ever transformed into such. The perfect sporidia are also very minute and numerous, being contained in asci borne in cups, which usually surround the spermogonia.

In several species of Dermatea the stylospores and spermatia co-exist, but they are disseminated before the appearance of the ascigerous receptacles, yet they are produced upon a common stroma not unlike that of Tubercularia.

In its early stage the common and well-known Bulgaria inquinans, which when mature looks like a black Peziza, is a little tubercle, the whole mass of which is divided into ramified lobes, the extremities of which become, towards the surface of the tubercle, receptacles from whence escape waves of spermatia which are colourless, or stylospores mixed with them which are larger and nearly black.

Amongst the Sphæriacei numerous instances might be cited of minute stylosporous bodies in consort with, or preceding, the ascigerous receptacles. A very familiar example may be found at the base of old nettle stems in what has been named Aposphæria acuta, but which truly are only the stylospores of the Sphæria coniformis, the perithecia of which flourish in company or in close proximity to them. Most of these bodies are so minute, delicate, and hyaline that the difficulties in the way of tracing them in their relations to the bodies with which they are associated are very great. Nevertheless there is strong presumption in favour of regarding some of them as performing the functions which the name applied to them indicates.

Professor de Bary cautiously refrains from accepting spermatia other than as doubtful or at least uncertain sexual bodies.[Q] He says that the Messrs. Tulasne have supposed that the spermogonia represented the male sex, and that the spermatia were analogous to spermatozoids. Their opinion depends on two plausible reasons,—the spermatia, in fact, do not germinate, and the development of the spermogonia generally precedes the appearance of the sporophorous organs, a double circumstance which reminds us of what is known of the spermatozoids and antheridia of other vegetables. It remained to discover which were the female organs which underwent fecundation from the spermatia.

Many organs placed at first amongst spermatia have been recognized by M. Tulasne as being themselves susceptible of germination, and consequently ought to take their place among legitimate spores. Then it must be considered that very many spores can only germinate under certain conditions. It is, therefore, for the present a doubtful question whether there exist really any spermatia incapable of germination, or if the default of germination of these corpuscles does not rather depend on the experiments hitherto attempted not having included the conditions required by the phenomena. Moreover, as yet no trace has been discovered of the female organs which are specially fecundated by the spermatia.

Finally, there exist in the Ascomycetes certain organs of reproduction, diverse spore-bearing apparatus, pycnidia, and others, which, like the spermogonia, usually precede ascophorous fruits. The real nature of the spermogonia and spermatia should therefore be regarded as, at present, very uncertain; as regards, however, the spermatia which have never been seen to germinate, perhaps it is as well not to absolutely reject the first opinion formed concerning them, or perhaps they might be thought to perform the part of androspores, attributing to that expression the meaning which Pringsheim gives it in the Conferoæ. The experiments performed with the spermatia which do not germinate, and with the spermogonia of the Uredines, do not, at any rate, appear to justify the reputed masculine or fecundative nature of these organs. The spermogonia constantly accompany or precede fruits of Æcidium, whence naturally follows the presumption that the first are in a sexual relation to the second. Still, when Tulasne cultivated Endophyllum sempervivum, he obtained on some perfectly isolated rosettes of Sempervivum some Æcidium richly provided with normal and fertile spores, without any trace of spermogonia or of spermatia.

[A]

M. Tulasne has devoted a chapter to the spermogonia of the Uredines in his memoir, to which we have already alluded.

[B]

Œersted, in “Verhandl der König. Dän. Gesell. Der Wissensch,” 1st January, 1865; De Bary, “Handbuch der Physiol. Botanik” (1866), p. 172; “Annales des Sci. Nat.” (5^me sér.), vol. v. (1866), p. 366.

[C]

Van Tieghem and Le Monnier, in “Annales des Sci. Nat.” (1873), vol. xvii. p. 261.

[D]

Brefeld, “Bot. Unt. uber Schimmelpilze,” p. 31.

[E]

De Bary, “Morphologie und Physiologie der Pilze,” cap. 5, p. 160; “Ann. des Sci. Nat.” (1866), p. 343.

[F]

Cornu, in “Ann. des Sci. Nat.” (5^me sér.), vol. xv. p. 1 (1872).

[G]

Pringsheim’s “Jahrbucher,” vol. ii. p. 169.

[H]

De Bary, in “Annales des Sciences Naturelles” (5^me sér.), vol. v. (1866), p. 343; Hoffmeister’s “Handbook” (Fungi), cap. v. p. 155.

[I]

De Bary, in “Annales des Sci. Nat.” (4^me sér.), vol. xx. p. 129.

[J]

De Bary, in “Annales des Sciences Naturelles” (5^me sér.), p. 343.

[K]

Woronin, in De Bary’s “Beitr. zur. Morph. und Physiol. der Pilze,” ii. (1866), pp. 1–11.

[L]

Tulasne, “Ann. des Sci. Nat.” (5^me sér.), October, 1866, p. 211.

[M]

Tulasne, “On the Phenomena of Copulation in certain Fungi,” in “Ann. des Sci. Nat.” (1866), p. 211.

[N]

De Bary, “Morphologie und Phys. der Pilze,” cap. v., p. 162.

[O]

Berkeley, in “Journ. Hort. Soc.” vol ii. p. 107; Tulasne, “Ann. d. Sc. Nat.” (4^me sér.), vol. ii. tab. 12.

[P]

Tulasne, “New Researches on the Reproductive Apparatus of Fungi;” “Comptes Rendus,” vol. xxxv. (1852), p. 841.

[Q]

De Bary, “Morphologie und Physiologie der Pilze,” cap. v. p. 168.

IX.

POLYMORPHISM.

A great number of very interesting facts have during late years been brought to light of the different forms which fungi assume in the course of their development. At the same time, we fear that a great many assumptions have been accepted for fact, and supposed connections and relations between two or three or more so-called species, belonging to different genera, have upon insufficient data been regarded as so many states or conditions of one and the same plant. Had the very pertinent suggestions of Professor de Bary been more generally acted upon, these suspicions would have been baseless. His observations are so valuable as a caution, that we cannot forbear prefacing our own remarks on this subject by quoting them.[A] In order to determine, he says, whether an organic form, an organ, or an organism, belongs to the same series of development as another, or that which is the same is developed from it, or vice versâ, there is only one way, viz., to observe how the second grows out of the first. We see the commencement of the second begin as a part of the first, perfect itself in connection with it, and at last it often becomes independent; but be it through spontaneous dismembering from the first, or that the latter be destroyed and the second remains, both their disunited bodies are always connected together in organic continuity, as parts of a whole (single one) that can cease earlier or later.

By observing the organic continuity, we know that the apple is the product of development of an apple-tree, and not hung on it by chance, that the pip of an apple is a product of the development of the apple, and that from the pip an apple-tree can at last be developed, that therewith all these bodies are members of a sphere of development or form. It is the same with every similar experience of our daily life, that where an apple-tree stands, many apples lie on the ground, or that in the place where apple-pips are sown seedlings, little apple-trees, grow out of the ground, is not important to our view of the course of development. Every one recognizes that in his daily life, because he laughs at a person who thinks a plum which lies under an apple-tree has grown on it, or that the weeds which appear among the apple seedlings come from apple-pips. If the apple-tree with its fruit and seed were microscopically small, it would not make the difference of a hair’s breadth in the form of the question or the method of answering it, as the size of the object can be of no importance to the latter, and the questions which apply to microscopical fungi are to be treated in the same manner.

If it then be asserted that two or several forms belong to a series of development of one kind, it can only be based on the fact of their organic continuity. The proof is more difficult than in large plants, partly because of the delicacy, minuteness, and fragility of the single parts, particularly the greater part of the mycelia, partly because of the resemblance of the latter in different species, and therefore follows the danger of confusing them with different kinds, and finally, partly in consequence of the presence of different kinds in the same substratum, and therefore the mixture not only of different sorts of mycelia, but also that different kinds of spores are sown. With some care and patience, these difficulties are in no way insurmountable, and they must at any rate be overcome; the organic continuity or non-continuity must be cleared up, unless the question respecting the course of development, and the series of forms of special kinds, be laid on one side as insolvable.

Simple and intelligible as these principles are, they have not always been acted upon, but partly neglected, partly expressly rejected, not because they were considered false, but because the difficulties of their application were looked upon as insurmountable. Therefore another method of examination was adopted; the spores of a certain form were sown, and sooner or later they were looked after to see what the seed had produced—not every single spore—but the seed en masse, that is, in other words, what had grown on that place where the seed had been sown. As far as it relates to those forms which are so widely spread, and above all grow in conjunction with one another—and that is always the case in the specimens of which we speak—we can never be sure that the spores of the form which we mean to test are not mingled with those of another species. He who has made an attentive and minute examination of this kind knows that we may be sure to find such a mixture, and that such an one was there can be afterwards decidedly proved. From the seed which is sown, these spores, for which the substratum was most suitable, will more easily germinate, and their development will follow the more quickly. The favoured germs will suppress the less favoured, and grow up at their expense. The same relation exists between them as between the seeds, germs, and seedlings of a sown summer plant, and the seeds which have been undesignedly sown with it, only in a still more striking manner, in consequence of the relatively quick development of the mildew fungus.

Therefore, that from the latter a decided form, or a mixture of several forms, is to be found sown on one spot, is no proof of their generic connection with one which has been sown for the purpose of experiments; and the matter will only be more confused if we call imagination to our aid, and place the forms which are found near one another, according to a real or fancied resemblance, in a certain series of development. All those statements on the sphere of form and connection, which have for their basis such a superficial work, and are not based on the clear exposition of the continuity of development, as by the origin of the connection of the Mucor with Penicillium, Oidium lactis and Mucor, Oidium and Penicillium, are rejected as unfounded.

A source of error, which can also interfere in the last-named superficial method of cultivation for experiments, is, viz., that heterogeneous unwished-for spores intrude themselves from without, among the seed which is sown, but that has been until now quite disregarded. It is of great importance in practice, but in truth, for our present purpose, synonymous with what we have already written. Those learned in the science of this kind of culture lay great stress on its importance, and many apparatuses have been constructed, called “purely cultivating machines,” for the purpose of destroying the spores which are contained in the substratum, and preventing the intrusion of those from without. The mixture in the seed which is sown has of course not been obviated. These machines may, perhaps, in every other respect, fulfil their purpose, but they cannot change the form of the question, and the most ingeniously constructed apparatus cannot replace the attention and intellect of the observer.[B]

Two distinct kinds of phenomena have been grouped under the term “polymorphy.” In one series two or more forms of fruit occur consecutively or simultaneously on the same individual, and in the other two or more forms appear on a different mycelium, on a different part of the same plant, or on a matrix wholly distinct and different; in the latter case the connection being attested or suspected circumstantially, in the former proved by the method suggested by De Bary. It will at once be conceded that in cases where actual growth and development substantiate the facts the polymorphy is undoubted, whilst in the other series it can at best be little more than suspected. We will endeavour to illustrate both these series by examples.

One of the first and earliest suspected cases of dualism, which long puzzled the older mycologists, was observed amongst the Uredines, and many years ago it was held that there must be some mysterious association between the “red rust” (Trichobasis ruligo vera) of wheat and grasses and the “corn mildew” (Puccinia graminis) which succeeded it. The simple spored rust first makes its appearance, and later the bilocular “mildew.” It is by no means uncommon to find the two forms in the same pustule. Some have held, without good reason, that the simple cells became afterwards divided and converted into Puccinia, but this is not the case; the uredo-spores are always simple, and remain so except in Uredo linearis, where every intermediate stage has been observed. Both are also perfect in their kind, and capable of germination.

What the precise relations between the two forms may be has as yet never been revealed to observers, but that the two forms belong to one species is not now doubted. Very many species of Puccinia have already been found associated with a corresponding Trichobasis, and of Phragmidium with a relative Lecythea, but it may be open to grave doubt whether some of the very many species associated by authors are not so classed upon suspicion rather than observation. We are ready to admit that the evidence is strong in favour of the dimorphism of a large number of species—it may be in all, but this awaits proof, or substantial presumption on good grounds. Up to the present we know that there are species of Trichobasis which have never been traced to association with a Puccinia, and doubtless there will be species of Puccinia for which no corresponding Uredo or Trichobasis can be found.

Tulasne remarks, in reference to Puccinia sonchi, in one of his memoirs, that this curious species exhibits, in effect, that a Puccinia may unite three sorts of reproductive bodies, which, taking part, constitute for the mycologists of the day three entirely different plants—a Trichobasis, a Uromyces, and a Puccinia. The Uredines are not less rich, he adds, in reproductive bodies of divers sorts than the Pyrenomycetes and the Discomycetes; and we should not be surprised at this, since it seems to be a law, almost constant in the general harmony of nature, that the smaller the organized beings are, the more their races are prolific.

In Puccinia variabilis, Grev., it is common to find a unicellular form, species of Trichobasis, in the same pustules. A like circumstance occurs with Puccinia violarum, Link., and Trichobasis violarum, B.; with Puccinia fallens, C., and Trichobasis fallens, Desm.; also with Puccinia menthæ, P., and Trichobasis Labiatarum, D. C. In Melampsora, again, the prismatic pseudospores of Melampsora salicina, Lev., are the winter fruits of Lecythea caprearum, Lev., as those of Melampsora populina, Lev., are of Lecythea populina, Lev. In the species of Lecythea themselves will be found, as De Bary[C] has shown, hyaline cysts of a larger size, which surround the pseudospores in the pustules in which they are developed.

A good illustration of dimorphism in one of the commonest of moulds is given by De Bary in a paper from which we have already quoted.[D] He writes thus:—In every household there is a frequent unbidden guest, which appears particularly on preserved fruits, viz., the mould which is called Aspergillus glaucus. It shows itself to the naked eye as a woolly floccy crust over the substance, first purely white, then gradually covered with little fine glaucous, or dark green dusty heads. More minute microscopical examination shows that the fungus consists of richly ramified fine filaments, which are partly disseminated in the substratum, and partly raised obliquely over it. They have a cylindrical form with rounded ends, and are divided into long outstretched members, each of which possesses the property which legitimatizes it as a vesicle in the ordinary sense of the word; it contains, enclosed within a delicate structureless wall, those bodies which bear the appearance of a finely granulated mucous substance, which is designated by the name of protoplasm, and which either equally fills the cells, or the older the cell the more it is filled with watery cavities called vacuoles.

All parts are at first colourless. The increase in the length of the filaments takes place through the preponderating growth near their points; these continually push forward, and, at a short distance from them, successive new partitions rise up, but at a greater distance, the growth in the length ceases. This kind of growth is called point growth. The twigs and branches spring up as lateral dilatations of the principal filament, which, once designed, enlarges according to the point growth. This point growth of every branch is, to a certain extent, unlimited. The filaments in and on the substratum are the first existing members of the fungus; they continue so long as it vegetates. As the parts which absorb nourishment from and consume the substance, they are called the mycelium. Nearly every fungus possesses a mycelium, which, without regard to the specific difference of form and size, especially shows the described nature in its construction and growth.

The superficial threads of the mycelium produce other filaments beside those numerous branches which have been described, and which are the fruit thread (carpophore) or conidia thread. These are on an average thicker than the mycelium threads, and only exceptionally ramified or furnished with partitions; they rise almost perpendicularly into the air, and attain a length of, on an average, half a millimetre, or one-fiftieth of an inch, but they seldom become longer, and then their growth is at an end. Their free upper end swells in a rounded manner, and from this is produced, on the whole of its upper part, rayed divergent protuberances, which attain an oval form, and a length almost equal to their radius, or, in weaker specimens, the diameter of the rounded head. The rayed divergent protuberances are the direct producers and bearers of the propagating cells, spores, or conidia, and are called sterigmata. Every sterigma at first produces at its point a little round protuberance, which, with a strong narrow basis, rests upon the sterigma. These are filled with protoplasm, swell more and more, and, after some time, separate themselves by a partition from the sterigma into independent cells, spores, or conidia.

The formation of the first spore takes place at the same end of the sterigma, and in the same manner a second follows, then a third, and so on; every one which springs up later pushes its predecessor in the direction of the axis of the sterigma in the same degree in which it grows itself; every successive spore formed from a sterigma remains for a time in a row with one another. Consequently every sterigma bears on its apex a chain of spores, which are so much the older, the farther they stand from the sterigma. The number of the links in a chain of spores reaches in normal specimens to ten or more. All sterigmata spring up at the same time, and keep pace with one another in the formation of the spores. Every spore grows for a time, according to its construction, and at last separates itself from its neighbours. The mass of dismembered spores forms that fine glaucous hue which is mentioned above. The spores, therefore, are articulated in rows, one after the other, from the ends of the sterigmata. The ripe spore, or conidium, is a cell of a round or broadly oval form, filled with a colourless protoplasm, and, if observed separately, is found to be provided with a brownish, finely verruculose, dotted wall.

Fig. 102.—a. Aspergillus glaucus; b. conidia; c. germinating conidium; d. conceptacle of Eurotium; e. ascus.

The same mycelium which forms the pedicel for the conidia when it is near the end of its development, forms by normal vegetation a second kind of fructification. It begins as delicate thin little branches, which are not to be distinguished by the naked eye, and which mostly in four or six turns, after a quickly terminated growth, wind their ends like a corkscrew. (Fig. 102.) The sinuations decrease in width more and more, till they at last reach close to one another, and the whole end changes from the form of a corkscrew into that of a hollow screw. In and on that screw-like body, a change of a complicated kind takes place, which is a productive process. In consequence of this, from the screw body a globose receptacle is formed, consisting of a thin wall of delicate cells, and a closely entwined row of cells surrounded by this dense mass (d). By the enlargement of all these parts the round body grows so much, that by the time it is ripe it is visible to the naked eye. The outer surface of the wall assumes a compactness and a bright yellow colour; the greater part of the cells of the inner mass become asci for the formation of sporidia, while they free themselves from the reciprocal union, take a broad oval form, and each one produces within its inner space eight sporidia (e). These soon entirely fill the ascus. When they are quite ripe, the wall of the conceptacle becomes brittle, and from irregular fissures, arising easily from contact, the colourless round sporidia are liberated.

The pedicels of both kinds of fruit are formed from the same mycelium in the order just described. If we examine attentively, we can often see both springing up close to one another from the same filament of a mycelium. This is not very easy in the close interlacing of the stalks of a mass of fungi in consequence of their delicacy and fragility. Before their connection was known, the conceptacles and the conidia pedicels were considered as organs of two very different species of fungi. The conceptacles were called Eurotium herbariorum, and the conidia bearers were called Aspergillus glaucus.

Fig. 103.—Erysiphe cichoracearum. a. Receptacle; o. mycelium. (De Bary.)

Allied to Eurotium is the group of Erysiphei, in which well-authenticated polymorphy prevails. These fungi are developed on the green parts of growing plants, and at first consist of a white mouldy stratum, composed of delicate mycelium, on which erect threads are produced, which break up into subglobose joints or conidia. The species on grass was named Oidium monilioides before its relationship was known, but undoubtedly this is only the conidia of Erysiphe graminis. In like manner the vine disease (Oidium Tuckeri) is most probably only the conidia of a species of Erysiphe, of which the perfect condition has not yet been discovered. On roses the old Oidium leucoconium is but the conidia of Sphærotheca pannosa, and so of other species. The Erysiphe which ultimately appears on the same mycelium consists of globose perithecia, externally furnished with thread-like appendages, and internally with asci containing sporidia. In this genus there are no less than five different forms of fruit,[E] the multiform threads on the mycelium, already alluded to as forms of Oidium, the asci contained in the sporangia, which is the proper fruit of the Erysiphe, larger stylospores which are produced in other sporangia, the smaller stylospores which are generated in the pycnidia, and separate sporules which are sometimes formed in the joints of the necklaces of the conidia. These forms are figured in the “Introduction to Cryptogamic Botany” from Sphærotheca Castagnei, which is the hop mildew.[F] The vine disease, hop mildew, and rose mildew, are the most destructive species of this group, and the constant annoyance of cultivators.

When first describing an allied fungus found on old paper, and named Ascotricha chartarum, the Rev. M. J. Berkeley called attention to the presence of globose conidia attached to the threads which surround the conceptacles,[G] and this occurred as long since as 1838. In a recent species of Chætomium found on old sacking, Chætomium griseum, Cooke,[H] we have found tufts in all respects similar externally to the Chætomium, but no perithecium was formed, naked conidia being developed apparently at the base of the coloured threads. In Chætomium funicolum, Cooke, a black mould was also found which may possibly prove to be its conidia, but at present there is no direct evidence.

The brothers Tulasne have made us acquainted with a greater number of instances amongst the Sphæriacei in which multiple organs of reproduction prevail. Very often old and decaying individuals belonging to species of Boletus will be found filled, and their entire substance internally replaced, by the threads and multitudinous spores of a golden yellow parasite, to which the name of Sepedonium chrysospermum has been given. According to Tulasne, this is merely a condition of a sphæriaceous fungus belonging to his genus Hypomyces.[I]

The same observers also first demonstrated that Trichoderma viride, P., was but the conidia-bearing stage of Hypocrea rufa, P., another sphæriaceous fungus. The ascigerous stroma of the latter is indeed frequently associated in a very close manner with the cushions of the pretended Trichoderma, or in other cases the same stroma will give rise to a different apparatus of conidia, of which the principal elements are acicular filaments, which are short, upright, and almost simple, and which give rise to small oval conidia which are solitary on the tips of the threads. Therefore this Hypocrea will possess two different kinds of conidia, as is the case in many species of Hypomyces.

A most familiar instance of dualism will be found in Nectria cinnabarina, of which the conidia form is one of the most common of fungi, forming little reddish nodules on all kinds of dead twigs.[J]

Fig. 104.—Twig with Tubercularia on the upper portion, Nectria on the lower.

Almost any small currant twig which has been lying on the ground in a damp situation will afford an opportunity of studying this phenomenon. The whole surface of the twig will be covered from end to end with little bright pink prominences, bursting through the bark at regular distances, scarcely a quarter of an inch apart. Towards one end of the twig probably the prominences will be of a deeper, richer colour, like powdered cinnabar. The naked eye is sufficient to detect some difference between the two kinds of pustules, and where the two merge into each other specks of cinnabar will be visible on the pink projections. By removing the bark it will be seen that the pink bodies have a sort of paler stem, which spreads above into a somewhat globose head, covered with a delicate mealy bloom. At the base it penetrates to the inner bark, and from it the threads of mycelium branch in all directions, confined, however, to the bark, and not entering the woody tissues beneath. The head, placed under examination, will be found to consist of delicate parallel threads compacted together to form the stem and head. Some of these threads are simple, others are branched, bearing here and there upon them delicate little bodies, which are readily detached, and which form the mealy bloom which covers the surface. These are the conidia, little slender cylindrical bodies, rounded at the ends.

Passing to the other bodies, which are of a deeper colour, it will soon be discovered that, instead of being simple rounded heads, each tubercle is composed of numerous smaller, nearly globose bodies, closely packed together, often compressed, all united to a base closely resembling the base of the other tubercles. If for a moment we look at one of the tubercles near the spot where the crimson tubercles seem to merge into the pink, we shall not only find them particoloured, but that the red points are the identical globose little heads just observed in clusters. This will lead to the suspicion, which can afterwards be verified, that the red heads are really produced on the stem or stroma of the pink tubercles.

Fig. 105.—Section of Tubercularia. c. Threads with conidia.[K]

A section of one of the red tubercles will show us how much the internal structure differs. The little subglobose bodies which spring from a common stroma or stem are hollow shells or capsules, externally granular, internally filled with a gelatinous nucleus. They are, indeed, the perithecia of a sphæriaceous fungus of the genus Nectria, and the gelatinous nucleus contains the fructification. Still further examination will show that this fructification consists of cylindrical asci, each enclosing eight elliptical sporidia, closely packed together, and mixed with slender threads called paraphyses.