TRICHOGASTRES.[T]--In their early stages the species contained in this group are not gelatinous, as in the _Myxogastres_, but are rather fleshy and firm. Very little has been added to our knowledge of structure in this group since 1839 and 1842, when one of us wrote to the following effect:--If a young plant of _Lycoperdon coelatum_ or _L. gemmatum_ be cut through and examined with a common pocket lens, it will be found to consist of a fleshy ma.s.s, perforated in every direction with minute elongated, reticulated, anastomosing, labyrinthiform cavities. The resemblance of these to the tubes of _Boleti_ in an early stage of growth, first led me to suspect that there must be some very close connection between them.

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

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

MYXOGASTRES.--At one time that celebrated mycologist, Professor De Bary, seemed disposed to exclude this group from the vegetable kingdom altogether, and relegate them to a companionship with amoeboid forms.

But in more recent works he seems to have reconsidered, and almost, if not entirely, abandoned, that disposition. These fungi, mostly minute, are characterized in their early stages by their gelatinous nature.

The substance of which they are then composed bears considerable resemblance to sarcode, and, did they never change from this, there might be some excuse for doubting as to their vegetable nature; but as the species proceed towards maturity they lose their mucilaginous texture, and become a ma.s.s of spores, intermixed with threads, surrounded by a cellular peridium. Take, for instance, the genus _Trichia_, and we have in the matured specimens a somewhat globose peridium, not larger than a mustard seed, and sometimes nearly of the same colour; this ultimately ruptures and exposes a ma.s.s of minute yellow spherical spores, intermixed with threads of the same colour.[V] These threads, when highly magnified, exhibit in themselves a spiral arrangement, which has been the basis of some controversy, and in some species these threads are externally spinulose. The chief controversy on these threads has been whether the spiral markings are external or internal, whether caused by twisting of the thread or by the presence of an external or internal fibre. The spiral appearance has never been called in question, only the structure from whence it arises, and this, like the striae of diatoms, is very much an open question. Mr. Currey held that the spiral appearance may be accounted for by supposing the existence of an accurate elevation in the wall of the cell, following a spiral direction from one end of the thread to the other. This supposition would, he thinks, accord well with the optical appearances, and it would account exactly for the undulations of outline to which he alludes. He states that he had in his possession a thread of _Trichia chrysosperma_, in which the spiral appearance was so manifestly caused by an elevation of this nature, in which it is so clear that no internal spiral fibre exists, that he did not think there could be a doubt in the mind of any person carefully examining it with a power of 500 diameters that the cause of the spiral appearance was not a spiral fibre. In _Arcyria_, threads of a different kind are present; they mostly branch and anastomose, and are externally furnished with prominent warts or spines, which Mr.

Currey[W] holds are also arranged in a spiral manner around the threads. In other Myxogastres, threads are also present without any appreciable spiral markings or spines. In the mature condition of these fungi, they so clearly resemble, and have such close affinities with, the Trichogastres that one is led almost to doubt whether it was not on hasty grounds, without due examination or consideration, that proposals were made to remove them from the society of their kindred.

[Ill.u.s.tration: FIG. 11.--_Arcyria incarnata_, with portion of threads and spore, magnified.]

Very little is known of the development of the spores in this group; in the early stages the whole substance is so pulpy, and in the latter so dusty, whilst the transition from one to the other is so rapid, that the relation between the spores and threads, and their mode of attachment, has never been definitely made out. It has been supposed that the spinulose projections from the capillitium in some species are the remains of pedicels from which, the spores have fallen, but there is no evidence beyond this supposition in its favour, whilst on the other hand, in _Stemonitis_, for instance, there is a profuse interlacing capillitium, and no spines have been detected. In order to strengthen the supposition, spines should be more commonly present.

The threads, or capillitium, form a beautiful reticulated network in _Stemonitis_, _Cribraria_, _Diachaea_, _Dictydium_, &c. In _Spumaria_, _Reticularia_, _Lycogala_, &c., they are almost obsolete.[X] In no group is the examination of the development of structure more difficult, for the reasons already alleged, than in the Myxogastres.

[Ill.u.s.tration: FIG. 12.--_Diachaea elegans._]

[Ill.u.s.tration: 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 debris 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 h.o.m.ogenous structure, then follows a cellular thicker stratum, bearing, towards the centre of the sporangia, delicate branched threads, or sporoph.o.r.es, 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.

SPHaeRONEMEI.--In this very large and, within certain limits, variable order, there is but little of interest as regards structure, which is not better ill.u.s.trated elsewhere; as, for instance, some sort of perithecium is always present, but this can be better studied in the _Sphaeriacei_. The spores are mostly very minute, borne on delicate sporoph.o.r.es, which originate from the inner surface of the perithecia, but the majority of so-called species are undoubtedly conditions of sphaeriaceous 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.

[Ill.u.s.tration: FIG. 14.--_Cyathus._ _a._ Sporangium. _b._ Section. _c._ Sporoph.o.r.e. _d._ Spores.]

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

In all cases the fructification is abundant, and the spores frequently ooze out in tendrils, or form a black ma.s.s above the spurious receptacle from which they issue.[a]

[Ill.u.s.tration: FIG. 15.--_Asterosporium Hoffmanni._]

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

[Ill.u.s.tration: FIG. 16.--Barren Cysts and Pseudospores of _Lecythea_.]

[Ill.u.s.tration: FIG. 17.--_Coleosporium Tussilaginis_, Lev.]

[Ill.u.s.tration: FIG. 18.--_Melampsora salicina._]

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

Similar oogonia are produced amongst the _Mucedines_ in the genus _Peronospora_, to which De Bary considers _Cystopus_ to be closely allied. At all events, this is a peculiarity of structure and development not as yet met with in any other of the _Caeomacei_. In _Uromyces_ is the nearest approach to the _Pucciniaei_; in fact, it is _Puccinia_ reduced to a single cell. The form of spore is usually more angular and irregular than in _Trichobasis_, and the pedicel is permanent. It may be remarked here, that of the foregoing genera, many of the species are not autonomous that have hitherto been included amongst them. This is especially true of _Lecythea_, _Trichobasis_, and, as it now appears, of _Uromyces_.[e]

[Ill.u.s.tration: FIG. 19.--_Cystopus candidus._]

[Ill.u.s.tration: FIG. 20.--_Xenodochus carbonarius._]

[Ill.u.s.tration: FIG. 21.--_Phragmidium bulbosum._]

PUCCINIaeI.--This group differs from the foregoing chiefly in having septate spores. The pustules, or sori, break through the cuticle in a similar manner, and here also no true peridium is present. In _Xenodochus_, the highest development of joints is reached, each spore being composed of an indefinite number, from ten to twenty cells. With it is a.s.sociated an unicellular yellow Uredine, of which it is a condition. Probably, in every species of the _Pucciniaei_, it may hereafter be proved, as it is now suspected, that an unicellular Uredine precedes or is a.s.sociated with it, forming a condition, or secondary form of fruit of that species. Many instances of that kind have already been traced by De Bary,[f] Tulasne, and others, and some have been a little too rashly surmised by their followers. In _Phragmidium_, the pedicel is much more elongated than in _Xenodochus_, and the spore is shorter, with fewer and a more definite number of cells for each species; Mr. Currey is of opinion that each cell of the spore in _Phragmidium_ has an inner globose cell, which he caused to escape by rupture of the outer cell wall as a sphaeroid nucleus,[g]

leading to the inference that each cell has its own individual power of germination and reproduction. In _Triphragmium_, there are three cells for each spore, two being placed side by side, and one superimposed. In one species, however, _Triphragmium deglubens_ (North American), the cells are arranged as in _Phragmidium_, so that this represents really a tricellular _Phragmidium_, linking the present with the latter genus. In _Puccinia_ the number of species is by far the most numerous; in this genus the spores are uniseptate, and, as in all the _Pucciniaei_, the peduncles are permanent. There is great variability in the compactness of the spores in the sori, or pulvinules.

In some species, the sori are so pulverulent that the spores are as readily dispersed as in the Uredines, in others they are so compact as to be separated from each other with great difficulty. As might be antic.i.p.ated, this has considerable effect on the contour of the spores, which in pulverulent species are shorter, broader, and more ovate than in the compact species. If a section of one of the more compact sori be made, it will be seen that the majority of the spores are side by side, nearly at the same level, their apices forming the external surface of the sori, but it will not be unusual to observe smaller and younger spores pushing up from the hymenial cells, between the peduncles of the elder spores, leading to the inference that there is a succession of spores produced in the same pulvinule. In _Podisoma_, a rather anomalous genus, the septate spores are immersed in a gelatinous stratum, and some authors have imagined that they have an affinity with the Tremellini, but this affinity is more apparent than real. The phenomena of germination, and their relations to _Roestelia_, if substantiated, establish their claim to a position amongst the _Pucciniaei_.[h] It seems to us that _Gymnosporangium_ does not differ generically from _Podisoma_. In a recently-characterized species, _Podisoma Ellisii_, the spores are bi-triseptate. This is, moreover, peculiar from the great deficiency in the gelatinous element. In another North American species, called _Gymnosporangium biseptatum_, Ellis, which is distinctly gelatinous, there are similar biseptate spores, but they are considerably broader and more obtuse. In other described species they are uniseptate.

[Ill.u.s.tration: FIG. 22.--Pseudospores of _Puccinia_.]

USTILAGINEI.--These fungi are now usually treated as distinct from the _Caeomacei_, to which they are closely related.[i] They are also parasitic on growing plants, but the spores are usually black or sooty, and never yellow or orange; on an average much smaller than in the _Caeomacei_. In _Tilletia_, the spores are spherical and reticulated, mixed with delicate threads, from whence they spring. In the best known species, _Tilletia caries_, they const.i.tute the "bunt"

of wheat. The peculiarities of germination will be alluded to hereafter. In _Ustilago_, the minute sooty spores are developed either on delicate threads or in compacted cells, arising first from a sort of semi-gelatinous, grumous stroma. It is very difficult to detect any threads a.s.sociated with the spores. The species attack the flowers and anthers of composite and polygonaceous plants, the leaves, culms, and germen of gra.s.ses, &c., and are popularly known as "s.m.u.ts." In _Urocystis_ and _Thecaphora_, the spores are united together into sub-globose bodies, forming a kind of compound spore. In some species of _Urocystis_, the union which subsists between them is comparatively slight. In _Thecaphora_, on the contrary, the complex spore, or agglomeration of spores, is compact, being at first apparently enclosed in a delicate cyst. In _Tuburcinia_, the minute cells are compacted into a hollow sphere, having lacunae communicating with the interior, and often exhibiting the remains of a pedicel.

[Ill.u.s.tration: FIG. 23.--_Thecaphora hyalina._]

[Ill.u.s.tration: FIG. 24.--_aecidium Berberidis._]

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

[Ill.u.s.tration: FIG. 25.--_Helminthosporium molle._]

HYPHOMYCETES.--The predominant feature in the structure of this order has already been intimated to consist in the development of the vegetative system under the form of simple or branched threads, on which the fruit is generated. The common name of mould is applied to them perhaps more generally than to other groups, although the term is too vague, and has been too vaguely applied to be of much service in giving an idea of the characteristics of this order. Leaving the smaller groups, and confining ourselves to the _Dematiei_ and the _Mucedines_, we shall obtain some notion of the prevalent structure.

In the former the threads are more or less carbonized, in the latter nearly colourless. One of the largest genera in _Dematiei_ is _Helminthosporium_. It appears on decaying herbaceous plants, and on old wood, forming effused black velvety patches. The mycelium, of coloured jointed threads, overlays and penetrates the matrix; from this arise erect, rigid, and usually jointed threads, of a dark brown, nearly black colour at the base, but paler towards the apex. In most cases these threads have an externally cortical layer, which imparts rigidity; usually from the apex, but sometimes laterally, the spores are produced. Although sometimes colourless, these are most commonly of some shade of brown, more or less elongated, and divided transversely by few or many septa. In _Helminthosporium Smithii_, the spores much exceed the dimensions of the threads;[m] in other species they are smaller. In _Dendryphium_, the threads and spores are very similar, except that the threads are branched at their apex, and the spores are often produced one at the end of another in a short chain.[n] In _Septosporium_ again, the threads and spores are similar, but the spores are pedicellate, and attached at or near the base; whilst in _Acrothecium_, with similar threads and spores, the latter are cl.u.s.tered together at the apex of the threads. In _Triposporium_, the threads are similar, but the spores are tri-radiate; and in _Helicoma_, the spores are twisted spirally. Thus, we might pa.s.s through all the genera to ill.u.s.trate 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.

[Ill.u.s.tration: FIG. 26.--_Acrothecium simplex._]

[Ill.u.s.tration: FIG. 27.--_Peronospora Arenariae._]

MUCEDINES.--Here, on the other hand, the threads, if coloured at all, are still delicate, more flexuous, with much thinner walls, and never invested with an external cortical layer. One of the most important and highly developed genera is _Peronospora_, the members of which are parasitic upon and destructive of living vegetables. It is to this genus that the mould of the too famous potato disease belongs.

Professor De Bary has done more than any other mycologist in the investigation and elucidation of this genus; and his monograph is a masterpiece in its way.[o] He was, however, preceded by Mr. Berkeley, and more especially by Dr. Montagne, by many years in elucidation of the structure of the flocci and conidia in a number of species.[p] In this genus, there is a delicate mycelium, which penetrates the intercellular pa.s.sages of living plants, giving rise to erect branched threads, which bear at the tips of their ultimate ramuli, sub-globose, ovate, or elliptic spores, or, as De Bary terms them--conidia. Deeply seated on the mycelium, within the substance of the foster plant, other reproductive bodies, called oogonia, originate. These are spherical, more or less warted and brownish, the contents of which become differentiated into vivacious zoospores, capable, when expelled, of moving in water by the aid of vibratile cilia. A similar structure has already been indicated in _Cystopus_, otherwise it is rare in fungi, if the _Saprolegniei_ be excluded. In _Botrytis_ and in _Polyactis_, the flocci and spores are similar, but the branches of the threads are shorter and more compact, and the septa are more common and numerous; the oogonia also are absent. De Bary has selected _Polyactis cinerea_, as it occurs on dead vine leaves, to ill.u.s.trate his views of the dualism which he believes himself to have discovered in this species. "It spreads its mycelium in the tissue which is becoming brown," he writes, "and this shows at first essentially the same construction and growth as that of the mycelium filaments of _Aspergillus_." On the mycelium soon appear, besides those which are spread over the tissue of the leaves, strong, thick, mostly fasciculate branches, which stand close to one another, breaking forth from the leaf and rising up perpendicularly, the conidia-bearers. They grow about 1 _mm._ long, divide themselves, by successively rising part.i.tions, 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 princ.i.p.al stem. Thus a system of branches appears, upon which, on a small scale, a bunch of grapes is represented. All the twigs soon end their growth; they all separate their inner s.p.a.ce from the princ.i.p.al stem, by means of a cross part.i.tion placed close to it.

All the ends, and also that of the princ.i.p.al 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 part.i.tion as in _Aspergillus_. The detached cells are the conidia of our fungus; only one is formed on each stalk. When the formation is completed in the whole of the panicle, the little branches which compose it are deprived of their protoplasm in favour of the conidia; it is the same with the under end of the princ.i.p.al stem, the limits of which are marked by a cross part.i.tion. 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 princ.i.p.al stem clearly appear as round circ.u.mscribed hilums, generally rather arched towards the exterior.

The development of the main stem is not ended here. It remains solid and filled with protoplasm as far as the portion which forms the end through its conidia. Its end, which is to be found among these pieces, becomes pointed after the ripening of the first panicle, pushes the end of the shrivelled member on one side, and grows to the same length as the height of one or two panicles, and then remains still, to form a second panicle similar to the first. This is later equally perfoliated as the first, then a third follows, and thus a large number of panicles are produced after and over one another on the same stem. In perfect specimens, every perfoliated panicle hangs loosely to its original place on the surface of the stem, until by shaking or the access of water to it, it falls immediately into the single conidia, or the remains of branches, and the already-mentioned oval hilums are left behind. Naturally, the stem becomes longer by every perfoliation; in luxuriant specimens the length can reach that of some lines. Its part.i.tion 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 princ.i.p.al stem.

[Ill.u.s.tration: FIG. 28.--_Polyactis cinerea._ _a._ Apex of hypha.]

The mycelium, which grows so exuberantly in the leaf, often brings forth many other productions, which are called _sclerotia_, and are, according to their nature, a thick bulbous tissue of mycelium filaments. Their formation begins with the profuse ramification of the mycelium threads in some place or other; generally, but not always, in the veins of the leaf; the intertwining twigs form an uninterrupted cavity, in which is often enclosed the shrivelling tissue of the leaf.

The whole body swells to a greater thickness than that of the leaf, and protrudes on the surface like a thickened spot. Its form varies from circular to fusiform; its size is also very unequal, ranging between a few lines and about half a millimetre in its largest diameter. At first it is colourless, but afterwards its outer layers of cells become round, of a brown or black colour, and it is surrounded by a black rind, consisting of round cells, which separate it from the neighbouring tissue. The tissue within the rind remains colourless; it is an entangled uninterrupted tissue of fungus filaments, which gradually obtain very solid, hard, cartilaginous coats. The sclerotium, which ripens as the rind becomes black, loosens itself easily from the place of its formation, and remains preserved after the latter is decayed.

[Ill.u.s.tration: FIG. 29.--_Peziza f.u.c.keliana._ _a._ Natural size. _b._ Section enlarged. _c._ Ascus and sporidia.]

The sclerotia are, here as in many other fungi, biennial organs, designed to begin a new vegetation after a state of apparent quietude, and to send forth special fruit-bearers. They may in this respect be compared to the bulbs and perennial roots of under shrubs. The usual time for the development of the sclerotia is late in the autumn, after the fall of the vine leaves. As long as the frost does not set in, new ones continually spring up, and each one attains to ripeness in a few days. If frost appears, it can lie dry a whole year, without losing its power of development. This latter commences when the sclerotium is brought into contact with damp ground during the usual temperature of our warmer seasons. If this occur soon, at the latest some weeks after it is ripe, new vegetation grows very quickly, generally after a few days; in several parts the colourless filaments of the inner tissue begin to send out cl.u.s.ters 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 cl.u.s.ters 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 circ.u.mstances, always form new asci for weeks at a time. The number of the already described utricle-bearers is different, according to the size of the sclerotium; smaller specimens usually produce only one, larger two to four. The size is regulated by that of the sclerotia, and ranges, in full-grown specimens, between one and more millimetres for the length of the stalk, and a half to three (seldom more) millimetres for the breadth of the disc.[q] For some time the conidia form, belonging to the Mucedines, has been known as _Botrytis cinerea_ (or _Polyactis cinerea_). The compact mycelium, or sclerotium, as an imperfect fungus, bore the name of _Sclerotium echinatum_, whilst to the perfect and cup-like form has been given the name of _Peziza f.u.c.keliana_. We have reproduced De Bary's life-history of this mould here, as an ill.u.s.tration of structure in the _Mucedines_, but hereafter we shall have to write of similar transformations when treating of polymorphism.

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

[Ill.u.s.tration: FIG. 30.--_Penicillium chartarum_, Cooke.]

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

[Ill.u.s.tration: FIG. 31.--_Mucor mucedo_, with three sporangia. _a._ Portion of frill with sporangiola.]

PHYSOMYCETES include, especially amongst the _Mucorini_, many most interesting and instructive species for study, which even very lately have occupied the attention of continental mycologists. Most of these phenomena are a.s.sociated 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 ill.u.s.trate this by the common _Mucor mucedo_: If we bring quite fresh horse-dung into a damp confined atmosphere, for example, under a bell-gla.s.s, 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 princ.i.p.al points it perfectly agrees with the sporangia of other species. Each of these white filaments is a sporangia-bearer. They spring from a mycelium which is spread in the dung, and appear singly upon it. Certain peculiarities in the form of the sporangium, and the little long cylindrical spores, which, when examined separately, are quite flat and colourless, are characteristic of the species. If the latter be sown in a suitable medium, for example, in a solution of sugar, they swell, and shoot forth germinating utricles, which quickly grow to mycelia, which bear sporangia. This is easily produced on the most various organic bodies, and _Mucor mucedo_ is therefore found spontaneously on every substratum which is capable of nourishing mildew, but on the above-named the most perfect and exuberant specimens are generally to be found. The sporangia-bearers are at first always branchless and without part.i.tions. After the sporangium is ripe, cross part.i.tions in irregular order and number often appear in the inner s.p.a.ce, and on the upper surface branches of different number and size, each of which forms a sporangium at its point. The sporangia which are formed later are often very similar, but sometimes very different, to those which first appeared, because their part.i.tion 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 part.i.tion 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 part.i.tion (called sporangiolum, to distinguish it from the larger ones), in which some, generally four, spores are formed in the manner already known. When the sporangiola are alone, they have such a peculiar appearance, with their richly-branched bearers, that they can be taken for something quite different to the organs of the _Mucor mucedo_, and were formerly not considered to belong to it. That they really belong to the _Mucor_ is shown by the princ.i.p.al filament which it bears, not always, but very often, ending with a large sporangium, which is characteristic of the _Mucor mucedo_; it is still more evident if we sow the spores of the sporangiolum, for, as it germinates, a mycelium is developed, which, near a simple bearer, can form large sporangia, and those form sporangiola, the first always considerably preponderating in number, and very often exclusively. If we examine a large number of specimens, we find every possible middle form between the simple or less branched sporangia-bearers and the typical sporangiola frills; and we arrive at last at the conclusion simply to place the latter among the varieties of form which the sporangia-bearer of the _Mucor mucedo_ shows, like every other typical organic form within certain limits. On the other hand, propagation organs, differing from those of the sporangia and their products, belong to _Mucor mucedo_, which may be termed conidia. On the dung (they are rare on any other substance) these appear at the same time, or generally somewhat later, than the sporangia-bearers, and are not unlike those to the naked eye. In a more accurate examination, they appear different; a thicker, part.i.tion-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 princ.i.p.al branches articulate on their somewhat broad tops, several spores and conidia, near one another; about fifteen to twenty are formed at the end of each little ramulus. The peculiarities and variations which so often appear in the ramification need not be discussed here. After the articulation of the conidia, their bearers sink together by degrees, and are quite destroyed. The ripe conidia are round like a ball, their surface is scarcely coloured, and almost wholly smooth. These conidioid forms were at first described as a separate species under the name of _Botrytis Jonesii_. How, then, do they belong to the _Mucor_?[t] That they appear gregariously is as little proof of an original relation to one another, here as elsewhere. Attempts to prove that the conidia and sporangia-bearers originate on one and the same mycelium filament may possibly hereafter succeed. Till now this has not been the case, and he who has ever tried to disentangle the ma.s.s of filaments which exuberantly covers the substratum of a _Mucor_ vegetation, which has reached so far as to form conidia, will not be surprised that all attempts have hitherto proved abortive. The suspicion of the connection founded on the gregariously springing up, and external resemblance, is fully justified, if we sow the conidia in a suitable medium, for example, in a solution of sugar. They here germinate and produce a mycelium which exactly resembles that of the _Mucor mucedo_, and, above all, they produce in profusion the typical sporangia of the same on its bearers.

The latter are till now alone reproductions of conidia-bearers, and have never been observed on mycelia which have grown out of conidia.

[Ill.u.s.tration: FIG. 32.--Small portion of _Botrytis Jonesii_.]

These phenomena of development appear in the _Mucor_ when it dwells on a damp substance, which must naturally contain the necessary nourishment for it, and is exposed to the atmospheric air. Its mycelium represents at first strong branched utricles without part.i.tions; 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 part.i.tions 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 circ.u.mstances, to new vegetating plants, as, for example, the bulbs of onions, &c.