Fig. 13.Fig. 13.—Cyathus vernicosus.
Fig. 13.—Cyathus vernicosus.
Nidulariacei.—This small group departs in some important particulars from the general type of structure present in the rest of the Gasteromycetes.[Y]The plants here included may be described under three parts, the mycelium, the peridium, and the sporangia. The mycelium is often plentiful, stout, rigid, interlacing, and coloured, running over the surface of the soil, or amongst the vegetable débris on which the fungi establish themselves. The peridia are seated upon this mycelium, and in most instances are at length open above, taking the form of cups, or beakers. These organs consist of three strata of tissue varying in structure, the external being fibrous, and sometimes hairy, the interior cellular and delicate, the intermediate thick and at length tough, coriaceous, and resistant.When first formed, the peridia are spherical, they then elongate and expand, the mouth being for some time closed by a veil, or diaphragm, which ultimately disappears. Within the cups lentil-shaped bodies are attached to the base and sides by elastic cords. These are the sporangia. Each of these has a complicated structure; externally there is a filamentous tunic, composed of interlaced fibres, sometimes called the peridiole; beneath this is the cortex, of compact homogenous structure, then follows a cellular thicker stratum, bearing, towards the centre of the sporangia, delicate branched threads, or sporophores, on which, at their extremities, the ovate spores are generated, sometimes in pairs, but normally, it would seem that they are quaternary on spicules, the threads being true basidia. The whole structure is exceedingly interesting and peculiar, and may be studied in detail in Tulasne’s memoir on this group.
Fig. 14.Fig. 14.—Cyathus.a.Sporangium.b.Section.c.Sporophore.d.Spores.
Fig. 14.—Cyathus.a.Sporangium.b.Section.c.Sporophore.d.Spores.
Sphæronemei.—In this very large and, within certain limits, variable order, there is but little of interest as regards structure, which is not better illustrated elsewhere; as, for instance, some sort of perithecium is always present, but this can be better studied in theSphæriacei. The spores are mostly very minute, borne on delicate sporophores, which originate from the inner surface of the perithecia, but the majority of so-called species are undoubtedly conditions of sphæriaceous fungi, either spermatogonia or pycnidia, and are of much more interest when studied in connection with the higher forms to which they belong.[Z]Probably the number of complete and autonomous species are very few.
Fig. 15.Fig. 15.—Asterosporium Hoffmanni.
Fig. 15.—Asterosporium Hoffmanni.
Melanconiei.—Here, again, are associated together a great number of what formerly were considered good species of fungi, but which are now known to be but conditions of other forms.One great point of distinction between these and the preceding is the absence of any true perithecium, the spores being produced in a kind of spurious receptacle, or from a sort of stroma. The spores are, as a rule, larger and much more attractive than inSphæronemei, and, in some instances, are either very fine, or very curious. Under this head we may mention the multiseptate spores ofCoryneum; the tri-radiate spores ofAsterosporium; the curious crested spores ofPestalozzia; the doubly crested spores ofDilophospora; and the scarcely less singular gelatinous coated spores ofCheirospora. In all cases the fructification is abundant, and the spores frequently ooze out in tendrils, or form a black mass above the spurious receptacle from which they issue.[a]
Fig. 16.Fig. 16.—Barren Cysts and Pseudospores ofLecythea.
Fig. 16.—Barren Cysts and Pseudospores ofLecythea.
Torulacei.—In this order there seems at first to be a considerable resemblance to theDematiei, except that the threads are almost obsolete, and the plant is reduced to chains of spores, without trace of perithecium, investing cuticle, or definite stroma. Sometimes the spores are simple, in other cases septate, and inSporochismaare at first produced in an investing cell. In most cases simple threads at length become septate, and are ultimately differentiated into spores, which separate at the joints when fully mature.
Fig. 17.Fig. 17.—Coleosporium Tussilaginis, Lev.
Fig. 17.—Coleosporium Tussilaginis, Lev.
Fig. 18.Fig. 18.—Melampsora salicina.
Fig. 18.—Melampsora salicina.
Cæomacei.—Of far greater interest are the Coniomycetous parasites on living plants. The present order includes those in which the spore[b]is reduced to a single cell; and here we may observe that, although many of them are now proved to be imperfect in themselves, and only forms or conditions of other fungals, we shall write of them here without regard to their duality. These originate, for the most part, within the tissues of living plants, and are developed outwards in pustules, which burst through the cuticle. The mycelium penetrates the intercellularpassages, and may sometimes be found in parts of the plants where the fungus does not develop itself. There is no proper excipulum or peridium, and the spores spring direct from a more compacted portion of the mycelium, or from a cushion-like stroma of small cells. InLecythea, the sub-globose spores are at first generated at the tips of short pedicels, from which they are ultimately separated; surrounding these spores arise a series of barren cells, or cysts, which are considerably larger the true spores, and colourless, while the spores are of some shade of yellow or orange.[c]InTrichobasis, the spores are of a similar character, sub-globose, and at first pedicellate; but there are no surrounding cysts, and the colour is more usually brown, although sometimes yellow. InUredo, the spores are at first generated singly, within a mother cell; they are globose, and either yellow or brown, without any pedicel. InColeosporium, there are two kinds of spores, those of a pulverulent nature, globose, which are sometimes produced alone at the commencement of the season, and others which originate as an elongated cell; this becomes septate, and ultimately separates at the joints. During the greater part of the year, both kinds of spores are to be found in the same pustule. InMelampsora, the winter spores are elongated and wedge-shaped, compacted together closely, and are only matured during winter on dead leaves; the summer spores are pulverulent and globose, being, in fact, what were until recently regardedas species ofLecythea. InCystopus, the spores are sub-globose, or somewhat angular, generated in a moniliform manner, and afterwards separating at the joints. The upper spore is always the oldest, continuous production of spores going on for some time at the base of the chain. Under favourable conditions of moisture, each of these spores, or conidia, as De Bary terms them, is capable of producing within itself a number of zoospores;[d]these ultimately burst the vesicle, move about by the aid of vibratile cilia, and at last settle down to germinate. Besides these, other reproductive bodies are generated upon the mycelium, within the tissues of the plant, in the form of globose oogonia, or resting spores, which, when mature, also enclose great numbers of zoospores. Similar oogonia are produced amongst theMucedinesin the genusPeronospora, to which De Bary considersCystopusto be closely allied. At all events, this is a peculiarity of structure and development not as yet met with in any other of theCæomacei. InUromycesis the nearest approach to thePucciniæi; in fact, it isPucciniareduced to a single cell. The form of spore is usually more angular and irregular than inTrichobasis, and the pedicel is permanent. It may be remarked here, that of the foregoing genera, many of the species are not autonomous that have hitherto been included amongst them. This is especially true ofLecythea,Trichobasis, and, as it now appears, ofUromyces.[e]
Fig. 19.Fig. 19.—Cystopus candidus.
Fig. 19.—Cystopus candidus.
Fig. 20.Fig. 20.—Xenodochus carbonarius.
Fig. 20.—Xenodochus carbonarius.
Pucciniæi.—This group differs from the foregoing chiefly in having septate spores. The pustules, or sori, break through the cuticle in a similar manner, and here also no true peridium is present. InXenodochus, the highest development of joints is reached, each spore being composed of an indefinite number, from ten to twenty cells. With it is associated an unicellularyellow Uredine, of which it is a condition. Probably, in every species of thePucciniæi, it may hereafter be proved, as it is now suspected, that an unicellular Uredine precedes or is associated with it, forming a condition, or secondary form of fruit of that species. Many instances of that kind have already been traced by De Bary,[f]Tulasne, and others, and some have been a little too rashly surmised by their followers. InPhragmidium, the pedicel is much more elongated than inXenodochus, and the spore is shorter, with fewer and a more definite number of cells for each species; Mr. Currey is of opinion that each cell of the spore inPhragmidiumhas an inner globose cell, which he caused to escape by rupture of the outer cell wall as a sphæroid nucleus,[g]leading to the inference that each cell has its own individual power of germination and reproduction. InTriphragmium, there are three cells for each spore, two being placed side by side, and one superimposed. In one species, however,Triphragmium deglubens(North American), the cells are arranged as inPhragmidium, so that this represents really a tricellularPhragmidium, linking the present with the latter genus. InPucciniathe number of species is by far the most numerous; in this genus the spores are uniseptate, and, as in all thePucciniæi, the peduncles are permanent. There is great variability in the compactness of the spores in the sori, or pulvinules. In some species, the sori are so pulverulent that the spores are as readily dispersed as in the Uredines, in others they are so compact as to be separated from eachother with great difficulty. As might be anticipated, this has considerable effect on the contour of the spores, which in pulverulent species are shorter, broader, and more ovate than in the compact species. If a section of one of the more compact sori be made, it will be seen that the majority of the spores are side by side, nearly at the same level, their apices forming the external surface of the sori, but it will not be unusual to observe smaller and younger spores pushing up from the hymenial cells, between the peduncles of the elder spores, leading to the inference that there is a succession of spores produced in the same pulvinule. InPodisoma, a rather anomalous genus, the septate spores are immersed in a gelatinous stratum, and some authors have imagined that they have an affinity with the Tremellini, but this affinity is more apparent than real. The phenomena of germination, and their relations toRœstelia, if substantiated, establish their claim to a position amongst thePucciniæi.[h]It seems to us thatGymnosporangiumdoes not differ generically fromPodisoma. In a recently-characterized species,Podisoma Ellisii, the spores are bi-triseptate. This is, moreover, peculiar from the great deficiency in the gelatinous element. In another North American species, calledGymnosporangium biseptatum, Ellis, which is distinctly gelatinous, there are similar biseptate spores, but they are considerably broader and more obtuse. In other described species they are uniseptate.
Fig. 21.Fig. 21.—Phragmidium bulbosum.
Fig. 21.—Phragmidium bulbosum.
Fig. 22.Fig. 22.—Pseudospores ofPuccinia.
Fig. 22.—Pseudospores ofPuccinia.
Ustilaginei.—These fungi are now usually treated as distinct from theCæomacei, to which they are closely related.[i]They are also parasitic on growing plants, but the spores are usually black or sooty, and never yellow or orange; on an average much smaller than in theCæomacei. InTilletia, the spores are spherical and reticulated, mixed with delicate threads, fromwhence they spring. In the best known species,Tilletia caries, they constitute the “bunt” of wheat. The peculiarities of germination will be alluded to hereafter. InUstilago, the minute sooty spores are developed either on delicate threads or in compacted cells, arising first from a sort of semi-gelatinous, grumous stroma. It is very difficult to detect any threads associated with the spores. The species attack the flowers and anthers of composite and polygonaceous plants, the leaves, culms, and germen of grasses, &c., and are popularly known as “smuts.” InUrocystisandThecaphora, the spores are united together into sub-globose bodies, forming a kind of compound spore. In some species ofUrocystis, the union which subsists between them is comparatively slight. InThecaphora, on the contrary, the complex spore, or agglomeration of spores, is compact, being at first apparently enclosed in a delicate cyst. InTuburcinia, the minute cells are compacted into a hollow sphere, having lacunæ communicating with the interior, and often exhibiting the remains of a pedicel.
Fig. 23.Fig. 23.—Thecaphora hyalina.
Fig. 23.—Thecaphora hyalina.
Fig. 24.Fig. 24.—Æcidium Berberidis.
Fig. 24.—Æcidium Berberidis.
Æcidiacei.—This group differs from the foregoing three groups prominently in the presence of a cellular peridium, which encloses the spores; hence some mycologists have not hesitated to propose their association with the Gasteromycetes, although every other feature in their structure seems to indicate a close affinity with theCæomacei. The pretty cups in the genusÆcidiumare sometimes scattered and sometimes collected in clusters, either with spermogonia in the centre or on the opposite surface. The cups are usually white, composed of regularly arranged bordered cells at length bursting at the apex, with the margins turned back and split into radiating teeth. The spores are commonly of a bright orange or golden yellow, sometimes white or brownish, and are produced in chains, or moniliformstrings, slightly attached to each other,[j]and breaking off at the summit at the same time that they continue to be produced at the base, so that for some time there is a successive production of spores. The spermogonia are not always readily detected, as they are much smaller than the peridia, and sometimes precede them. The spermatia are expelled from the lacerated and fringed apices, and are very minute and colourless. InRœsteliathe peridia are large, growing in company, and splitting longitudinally in many cases, or by a lacerated mouth. In most instances, the spores are brownish, but in a splendid species from North America (Rœstelia aurantiaca, Peck), recently characterized, they are of a bright orange. If Œrsted is correct in his observations, which await confirmation, these species are all related to species ofPodisomaas a secondary form of fruit.[k]In theRœsteliaof the pear-tree, as well as in that of the mountain ash, the spermogonia will be found either in separate tufts on discoloured spots, or associated with theRœstelia, InPeridermiumthere is very little structural difference fromRœstelia, and the species are all found on coniferous trees. InEndophyllum, the peridia are immersed in the succulent substance of the matrix; whilst inGraphiola, there is a tougher and withal double peridium, the inner of which forms a tuft of erect threads resembling a small brush.[l]
Fig. 25.Fig. 25.—Helminthosporium molle.
Fig. 25.—Helminthosporium molle.
Hyphomycetes.—The predominant feature in the structure of this order has already been intimated to consist in the development of the vegetative system under the form of simple or branched threads, on which the fruit is generated. The common name of mould is applied to them perhaps more generally than to other groups, although the term is too vague, and has been too vaguely applied to be of much service in giving an idea of the characteristics of this order. Leaving the smaller groups, and confining ourselves to theDematieiand theMucedines, weshall obtain some notion of the prevalent structure. In the former the threads are more or less carbonized, in the latter nearly colourless. One of the largest genera inDematieiisHelminthosporium. It appears on decaying herbaceous plants, and on old wood, forming effused black velvety patches. The mycelium, of coloured jointed threads, overlays and penetrates the matrix; from this arise erect, rigid, and usually jointed threads, of a dark brown, nearly black colour at the base, but paler towards the apex. In most cases these threads have an externally cortical layer, which imparts rigidity; usually from the apex, but sometimes laterally, the spores are produced. Although sometimes colourless, these are most commonly of some shade of brown, more or less elongated, and divided transversely by few or many septa. InHelminthosporium Smithii, the spores much exceed the dimensions of the threads;[m]in other species they are smaller. InDendryphium, the threads and spores are very similar, except that the threads are branched at their apex, and the spores are often produced one at the end of another in a short chain.[n]InSeptosporiumagain, the threads and spores are similar, but the spores are pedicellate, and attached at or near the base; whilst inAcrothecium, with similar threads and spores, the latter are clustered together at the apex of the threads. InTriposporium, the threads are similar, but the spores are tri-radiate; and inHelicoma, the spores are twisted spirally. Thus, we might passthrough all the genera to illustrate this chief feature of coloured, septate, rather rigid, and mostly erect threads, bearing at some point spores, which in most instances are elongated, coloured, and septate.
Fig. 26.Fig. 26.—Acrothecium simplex.
Fig. 26.—Acrothecium simplex.
Fig. 27.Fig. 27.—Peronospora Arenariæ.
Fig. 27.—Peronospora Arenariæ.
Mucedines.—Here, on the other hand, the threads, if coloured at all, are still delicate, more flexuous, with much thinner walls, and never invested with an external cortical layer. One of the most important and highly developed genera isPeronospora, the members of which are parasitic upon and destructive of living vegetables. It is to this genus that the mould of the too famous potato disease belongs. Professor De Bary has done more than any other mycologist in the investigation and elucidation of this genus; and his monograph is a masterpiece in its way.[o]He was, however, preceded by Mr. Berkeley, and more especially by Dr. Montagne, by many years in elucidation of the structure of the flocci and conidia in a number of species.[p]In this genus, there is a delicate mycelium, which penetrates the intercellular passages of living plants, giving rise to erect branched threads, which bear at the tips of their ultimate ramuli, sub-globose, ovate, or elliptic spores, or, as De Bary terms them—conidia. Deeply seated on the mycelium, within the substance of the foster plant, other reproductive bodies, called oogonia, originate. These are spherical, more orless warted and brownish, the contents of which become differentiated into vivacious zoospores, capable, when expelled, of moving in water by the aid of vibratile cilia. A similar structure has already been indicated inCystopus, otherwise it is rare in fungi, if theSaprolegnieibe excluded. InBotrytisand inPolyactis, the flocci and spores are similar, but the branches of the threads are shorter and more compact, and the septa are more common and numerous; the oogonia also are absent. De Bary has selectedPolyactis cinerea, as it occurs on dead vine leaves, to illustrate his views of the dualism which he believes himself to have discovered in this species. “It spreads its mycelium in the tissue which is becoming brown,” he writes, “and this shows at first essentially the same construction and growth as that of the mycelium filaments ofAspergillus.” On the mycelium soon appear, besides those which are spread over the tissue of the leaves, strong, thick, mostly fasciculate branches, which stand close to one another, breaking forth from the leaf and rising up perpendicularly, the conidia-bearers. They grow about 1mm.long, divide themselves, by successively rising partitions, into some prominent cylindrical linked cells, and then their growth is ended, and the upper cell produces near its point three to six branches almost standing rectangularly. Of these the under ones are the longest, and they again shoot forth from under their ends one or more still shorter little branches. The nearer they are to the top, the shorter are the branches, and less divided; the upper ones are quite branchless, and their length scarcely exceeds the breadth of the principal stem. Thus a system of branches appears, upon which, on a small scale, a bunch of grapes is represented. All the twigs soon end theirgrowth; they all separate their inner space from the principal stem, by means of a cross partition placed close to it. All the ends, and also that of the principal stem, swell about the same time something like a bladder, and on the upper free half of each swelling appear again, simultaneously, several fine protuberances, close together, which quickly grow to little oval bladders filled with protoplasm, and resting on their bearers with a sub-sessile, pedicellate, narrow basis, and which at length separate themselves through a partition as inAspergillus. The detached cells are the conidia of our fungus; only one is formed on each stalk. When the formation is completed in the whole of the panicle, the little branches which compose it are deprived of their protoplasm in favour of the conidia; it is the same with the under end of the principal stem, the limits of which are marked by a cross partition. The delicate wall of these parts shrinks up until it is unrecognizable; all the conidia of the panicle approach one another to form an irregular grape-like bunch, which rests loosely on the bearer, and from which it easily falls away as dust. If they be brought into water they fall off immediately; only the empty, shrivelled, delicate skins are to be found on the branch which bore them, and the places on which they are fixed to the principal stem clearly appear as round circumscribed hilums, generally rather arched towards the exterior. The development of the main stem is not ended here. It remains solid and filled with protoplasm as far as the portion which forms the end through its conidia. Its end, which is to be found among these pieces, becomes pointed after the ripening of the first panicle, pushes the end of the shrivelled member on one side, and grows to the same length as the height of one or two panicles, and then remains still, to form a second panicle similar to the first. This is later equally perfoliated as the first, then a third follows, and thus a large number of panicles are produced after and over one another on the same stem. In perfect specimens, every perfoliated panicle hangs loosely to its original place on the surface of the stem, until by shaking or the access of water to it, it falls immediately into the single conidia, or the remains of branches, and thealready-mentioned oval hilums are left behind. Naturally, the stem becomes longer by every perfoliation; in luxuriant specimens the length can reach that of some lines. Its partition is already, by the ripening of the first panicle from the beginning of its foundation, strong and brown; it is only colourless at the end which is extending, and in all new formations. During all these changes the filament remains either unbranched, except as regards the transient panicles, or it sends out here and there, at the perfoliated spots, especially from the lower ones, one or two strong branches, standing opposite one another and resembling the principal stem.
Fig. 28.Fig. 28.—Polyactis cinerea.a.Apex of hypha.
Fig. 28.—Polyactis cinerea.a.Apex of hypha.
The mycelium, which grows so exuberantly in the leaf, often brings forth many other productions, which are calledsclerotia, and are, according to their nature, a thick bulbous tissue of mycelium filaments. Their formation begins with the profuse ramification of the mycelium threads in some place or other; generally, but not always, in the veins of the leaf; the intertwining twigs form an uninterrupted cavity, in which is often enclosed the shrivelling tissue of the leaf. The whole body swells to a greater thickness than that of the leaf, and protrudes on the surface like a thickened spot. Its form varies from circular to fusiform; its size is also very unequal, ranging between a few lines and about half a millimetre in its largest diameter. At first it is colourless, but afterwards its outer layers of cells become round, of a brown or black colour, and it is surrounded by a black rind, consisting of round cells, which separate it from the neighbouring tissue. The tissue within the rind remains colourless; it is an entangled uninterrupted tissue of fungus filaments, which gradually obtain very solid, hard, cartilaginous coats. The sclerotium, which ripens as the rind becomes black, loosens itself easily from the place of its formation, and remains preserved after the latter is decayed.
Fig. 29.Fig. 29.—Peziza Fuckeliana.a.Natural size.b.Section enlarged.c.Ascus and sporidia.
Fig. 29.—Peziza Fuckeliana.a.Natural size.b.Section enlarged.c.Ascus and sporidia.
The sclerotia are, here as in many other fungi, biennial organs, designed to begin a new vegetation after a state of apparent quietude, and to send forth special fruit-bearers. They may in this respect be compared to the bulbs and perennial roots of under shrubs. The usual time for the development ofthe sclerotia is late in the autumn, after the fall of the vine leaves. As long as the frost does not set in, new ones continually spring up, and each one attains to ripeness in a few days. If frost appears, it can lie dry a whole year, without losing its power of development. This latter commences when the sclerotium is brought into contact with damp ground during the usual temperature of our warmer seasons. If this occur soon, at the latest some weeks after it is ripe, new vegetation grows very quickly, generally after a few days; in several parts the colourless filaments of the inner tissue begin to send out clusters of strong branches, which, breaking through the black rind, stretch themselves up perpendicularly towards the surface, separate from one another, and then take all the characteristics of the conidia-bearers. Many such clusters can be produced on one sclerotium, so that soon the greater part of the surface is covered by filamentous conidia-bearers with their panicles. The colourless tissue of the sclerotium disappears in the same degree as the conidia-bearers grow, and at last the black rind remains behind empty and shrivelled. If we bring, after many months, for the first time, the ripe sclerotium, in damp ground, in summer or autumn, after it has ripened, the further development takes place more slowly, and in an essentially different form. It is true that from the inner tissue numerous filamentous branches shoot forth at the cost of this growing fascicle, and break through the black rind, but its filaments remain strongly bound, in an almost parallel situation, to a cylindrical cord, which for a time lengthens itself and spreads out its free end to a flat plate-like disc. This is always formed of strongly united threads, ramifications of the cylindrical cord. On the free upper surface of the disc, the filaments shoot forth innumerable branches, which, growing to the same height, thick and parallel with one another, cover the before-named disc.Some remain narrow and cylindrical, are very numerous, and produce fine hairs (paraphyses); others, also very numerous, take the form of club-like ampulla cells, and each one forms in its interior eight free swimming oval spores. Those ampulla cells are sporidiiferous asci. After the spores have become ripe, the free point of the utricle bursts, and the spores are scattered to a great distance by a mechanism which we will not here further describe. New ampullas push themselves between those which are ripening and withering; a disc can, under favourable circumstances, always form new asci for weeks at a time. The number of the already described utricle-bearers is different, according to the size of the sclerotium; smaller specimens usually produce only one, larger two to four. The size is regulated by that of the sclerotia, and ranges, in full-grown specimens, between one and more millimetres for the length of the stalk, and a half to three (seldom more) millimetres for the breadth of the disc.[q]For some time the conidia form, belonging to the Mucedines, has been known asBotrytis cinerea(orPolyactis cinerea). The compact mycelium, or sclerotium, as an imperfect fungus, bore the name ofSclerotium echinatum, whilst to the perfect and cup-like form has been given the name ofPeziza Fuckeliana. We have reproduced De Bary’s life-history of this mould here, as an illustration of structure in theMucedines, but hereafter we shall have to write of similar transformations when treating of polymorphism.
Fig. 30.Fig. 30.—Penicillium chartarum, Cooke.
Fig. 30.—Penicillium chartarum, Cooke.
The form of the threads, and the form and disposition of the spores, vary according to the genera of which this order is composed. InOidiumthe mostly simple threads break up into joints. Many of the former species are now recognized as conditions ofErysiphe. InAspergillus, the threads are simple and erect, with a globose head, around which are clustered chains of simple spores. InPenicillium, the lower portion of the threads is simple, but they are shortly branched at the apex, the branches being terminated by necklaces of minute spores. InDactylium,the threads are branched, but the spores are collected in clusters usually, and are moreover septate. In other genera similar distinctions prevail. These two groups of black moulds and white moulds are the noblest, and contain the largest number of genera and species amongst theHyphomycetes. There is, however, the small group ofIsariacei, in which the threads are compacted, and a semblance of such hymenomycetal forms asClavariaandPterulais the result, but it is doubtful if this group contains many autonomous species. In another small group, theStilbacei, there is a composite character in the head, or receptacle,[r]and in the stem when the latter is present. Many of these, again, asTubercularia,Volutella,Fusarium, &c., contain doubtful species. InSepedonieiandTrichodermacei, the threads are reduced to a minimum, and the spores are such a distinctive element that through these groups theHyphomycetesare linked with theConiomycetes. These groups, however, are not of sufficient size or importance to demand from us, in a work of this character, anything more than the passing allusion which we have given to them.
We come now to consider the structure in the Sporidiifera, in which the fructifying corpuscles or germs, whether called spores or sporidia, are generated within certain privileged cysts, usually in definite numbers. In systematic works, these are included under two orders, thePhysomycetesand theAscomycetes. The former of these consists of cyst-bearing moulds, and from their nearest affinity to the foregoing will occupy the first place.
Fig. 31.Fig. 31.—Mucor mucedo, with three sporangia.a.Portion of frill with sporangiola.
Fig. 31.—Mucor mucedo, with three sporangia.a.Portion of frill with sporangiola.
Physomycetesinclude, especially amongst theMucorini, many most interesting and instructive species for study, which even very lately have occupied the attention of continental mycologists. Most of these phenomena are associated more or less with reproduction, and as such will have to be adverted to again,but there are points in the structure which can best be alluded to here. Again taking Professor de Bary’s researches as our guide,[s]we will illustrate this by the commonMucor mucedo: If we bring quite fresh horse-dung into a damp confined atmosphere, for example, under a bell-glass, there appears on its surface, after a few days, an immense white mildew. Upright strong filaments of the breadth of a hair raise themselves over the surface, each of them soon shows at its point a round little head, which gradually becomes black, and a closer examination shows us that in all principal points it perfectly agrees with the sporangia of other species. Each of these white filaments is a sporangia-bearer. They spring from a mycelium which is spread in the dung, and appear singly upon it. Certain peculiarities in the form of the sporangium, and the little long cylindrical spores, which, when examined separately, are quite flat and colourless, are characteristic of the species. If the latter be sown in a suitable medium, for example, in a solution of sugar, they swell, and shoot forth germinating utricles, which quickly grow to mycelia, which bear sporangia. This is easily produced on the most various organic bodies, andMucor mucedois therefore found spontaneously on every substratum which is capable of nourishing mildew, but on the above-named the most perfect and exuberant specimens are generally to be found. The sporangia-bearers are at first always branchless and without partitions. After the sporangium is ripe, cross partitions in irregular order and number often appear in the inner space, and on the uppersurface branches of different number and size, each of which forms a sporangium at its point. The sporangia which are formed later are often very similar, but sometimes very different, to those which first appeared, because their partition is very thick and does not fall to pieces when it is ripe, but irregularly breaks off, or remains entire, enclosing the spores, and at last falls to the ground, when the fungus withers. The cross partition which separates the sporangia from its bearers is in those which are first formed (which are always relatively thicker sporangia) very strongly convex, while those which follow later are often smaller, and in little weak specimens much less arched, and sometimes quite straight. After a few days, similar filaments generally show themselves on the dung between the sporangia-bearers, which appear to the naked eye to be provided with delicate white frills. Where such an one is to be found, two to four rectangular expanding little branches spring up to the same height round the filament. Each of these, after a short and simple process, branch out into a furcated form; the furcations being made in such a manner that the ends of the branch at last so stand together that their surface forms a ball. Finally, each of the ends of a branch swells to a little round sporangium, which is limited by a partition (called sporangiolum, to distinguish it from the larger ones), in which some, generally four, spores are formed in the manner already known. When the sporangiola are alone, they have such a peculiar appearance, with their richly-branched bearers, that they can be taken for something quite different to the organs of theMucor mucedo, and were formerly not considered to belong to it. That they really belong to theMucoris shown by the principal filament which it bears, not always, but very often, ending with a large sporangium, which is characteristic of theMucor mucedo; it is still more evident if we sow the spores of the sporangiolum, for, as it germinates, a mycelium is developed, which, near a simple bearer, can form large sporangia, and those form sporangiola, the first always considerably preponderating in number, and very often exclusively. If we examine a large number of specimens, we find every possible middle form between the simpleor less branched sporangia-bearers and the typical sporangiola frills; and we arrive at last at the conclusion simply to place the latter among the varieties of form which the sporangia-bearer of theMucor mucedoshows, like every other typical organic form within certain limits. On the other hand, propagation organs, differing from those of the sporangia and their products, belong toMucor mucedo, which may be termed conidia. On the dung (they are rare on any other substance) these appear at the same time, or generally somewhat later, than the sporangia-bearers, and are not unlike those to the naked eye. In a more accurate examination, they appear different; a thicker, partition-less filament rises up and divides itself, generally three-forked, at the length of one millimetre, into several series of branchlets. The forked branches of the last series bear under their points, which are mostly capillary, short erect little ramuli, and these, with which the ends of the principal branches articulate on their somewhat broad tops, several spores and conidia, near one another; about fifteen to twenty are formed at the end of each little ramulus. The peculiarities and variations which so often appear in the ramification need not be discussed here. After the articulation of the conidia, their bearers sink together by degrees, and are quite destroyed. The ripe conidia are round like a ball, their surface is scarcely coloured, and almost wholly smooth. These conidioid forms were at first described as a separate species under the name ofBotrytis Jonesii. How, then, do they belong to theMucor?[t]That they appear gregariously is as little proof of an original relation to one another, here as elsewhere. Attempts to prove that the conidia and sporangia-bearers originate on one and the same mycelium filament may possibly hereafter succeed. Till now this has not been the case,and he who has ever tried to disentangle the mass of filaments which exuberantly covers the substratum of aMucorvegetation, which has reached so far as to form conidia, will not be surprised that all attempts have hitherto proved abortive. The suspicion of the connection founded on the gregariously springing up, and external resemblance, is fully justified, if we sow the conidia in a suitable medium, for example, in a solution of sugar. They here germinate and produce a mycelium which exactly resembles that of theMucor mucedo, and, above all, they produce in profusion the typical sporangia of the same on its bearers. The latter are till now alone reproductions of conidia-bearers, and have never been observed on mycelia which have grown out of conidia.
Fig. 32.Fig. 32.—Small portion ofBotrytis Jonesii.
Fig. 32.—Small portion ofBotrytis Jonesii.
These phenomena of development appear in theMucorwhen it dwells on a damp substance, which must naturally contain the necessary nourishment for it, and is exposed to the atmospheric air. Its mycelium represents at first strong branched utricles without partitions; the branches are of the higher order, mostly divided into rich and very fine-pointed ramuli. In old mycelium, and also in the sporangia-bearers, the contents of which are mostly used for the formation of spores, and the substratum of which is exhausted for our fungus, short stationary pieces, filled with protoplasm, are very often formed into cells through partitions in order to produce spores, that is, grow to a new fruitful mycelium. These cells are called gemmules, brooding cells, and resemble such vegetable buds and sprouts of foliaceous plants which remain capable of development after the organs of vegetation are dead, in order to grow, under suitable circumstances, to new vegetating plants, as, for example, the bulbs of onions, &c.
If we bring a vegetating mycelium ofMucor mucedointo a medium which contains the necessary nourishment for it, but excluded from the free air, the formation of sporangia takes place very sparingly or not at all, but that of gemmules is very abundant. Single interstitial pieces of the ramuli, or even whole systems of branches, are quite filled with a rich greasy protoplasm; the short pieces and ends are bound by partitions whichform particular, often tun-like or globular cells; the longer ones are changed, through the formation of cross partitions, into chains of similar cells; the latter often attain by degrees strong, thick walls, and their greasy contents often pass into innumerable drops of a very regular globular form and of equal size. Similar appearances show themselves after the sowing of spores, which are capable of germinating in the medium already described, from which the air is excluded. Either short germinating utricles shoot forth, which soon form themselves into rows of gemmules, or the spores swell to large round bladders filled with protoplasm, and shoot forth on various parts of their surface innumerable protuberances, which, fixing themselves with a narrow basis, soon become round vesiculate cells, and on which the same sprouts which caused their production are repeated, formations which remind us of the fungus of fermentation called globular yeast. Among all the known forms of gemmules we find a variety which are intermediate, all of which show, when brought into a normal condition of development, the same proportion, and the same germination, as those we first described.
We have detailed rather at length the structure and development of one of the most common of the Mucors, which will serve as an illustration of the order. Other distinctions there may be which are of more interest as defining the limits of genera, except such as may be noticed when we come to write more specially of reproduction.
Ascomycetes.—Passing now to theAscomycetes, which are especially rich in genera and species, we must first, and but superficially, allude toTuberacei, an order of sporidiiferous fungi of subterranean habit, and rather peculiar structure.[u]In this order an external stratum of cells forms a kind of perithecium, which is more or less developed in different genera. This encloses the hymenium, which is sinuous, contorted, and twisted, often forming lacunæ. The hymenium in some genera consists of elongated, nearly cylindrical asci, enclosing a definite number of sporidia; in the true truffles and their immediate allies, the asci are broadsacs, containing very large and beautiful, often coloured, sporidia. These latter have either a smooth, warted, spinulose, or lacunose epispore, and, as will be seen from the figures in Tulasne’s Monograph,[v]or those in the last volume of Corda’s great work,[w]are attractive microscopical objects. In some cases, it is not difficult to detect paraphyses, but in others they would seem to be entirely absent. A comparatively large number have been discovered and recorded in Great Britain,[x]but of those none are more suitable for study of general structure than the ordinary truffle of the markets.
The structure of the remaining Ascomycetes can be studied under two groups,i.e., the fleshy Ascomycetes, or, as they have been termed, the Discomycetes, and the hard, or carbonaceous Ascomycetes, sometimes called the Pyrenomycetes. Neither of these names gives an accurate idea of the distinctions between the two groups, in the former of which the discoid form is not universal, and the latter contains somewhat fleshy forms. But in the Discomycetes the hymenium soon becomes more or less exposed, and in the latter it is enclosed in a perithecium. The Discomycetes are of two kinds, the pileate and the cup-shaped. Of the pileate such a genus asGyromitraorHelvellais, in a certain sense, analogous to the Agarics amongstHymenomycetes, with a superior instead of an inferior hymenium, and enclosed, not naked, spores. Again,Geoglossumis somewhat analogous toClavaria. Amongst the cup-shaped,Pezizais an AscomycetousCyphella. But these are perhaps more fanciful than real analogies.
Recently Boudier has examined one group of the cup-shaped Discomycetes, theAscobolei, and, by making a somewhat free use of his Memoir,[y]we may arrive at a general idea of the structure in the cupulate Discomycetes. They present themselves atfirst under the form of a small rounded globule, and almost entirely cellular. This small globule, the commencement of the receptacle, is not long in increasing, preserving its rounded form up to the development of the asci. At this period, under the influence of the rapid growth of these organs, it soon produces at its summit a fissure of the external membrane, which becomes a more marked depression in the marginate species. The receptacle thus formed increases rapidly, becomes plane, more convex, or more or less undulated at the margin, if at all of large size. Fixed to the place where it is generated by some more or less abundant mycelioid filaments, the receptacle becomes somewhat cup-shaped and either stipitate or sessile, composed of the receptacle proper and the hymenium.