If we bring a vegetating mycelium of _Mucor mucedo_ into a medium which contains the necessary nourishment for it, but excluded from the free air, the formation of sporangia takes place very sparingly or not at all, but that of gemmules is very abundant. Single interst.i.tial 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 part.i.tions which form particular, often tun-like or globular cells; the longer ones are changed, through the formation of cross part.i.tions, into chains of similar cells; the latter often attain by degrees strong, thick walls, and their greasy contents often pa.s.s 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 ill.u.s.tration 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.--Pa.s.sing now to the _Ascomycetes_, which are especially rich in genera and species, we must first, and but superficially, allude to _Tuberacei_, an order of sporidiiferous fungi of subterranean habit, and rather peculiar structure.[u] In this order an external stratum of cells forms a kind of perithecium, which is more or less developed in different genera. This encloses the hymenium, which is sinuous, contorted, and twisted, often forming lacunae. The hymenium in some genera consists of elongated, nearly cylindrical asci, enclosing a definite number of sporidia; in the true truffles and their immediate allies, the asci are broad sacs, containing very large and beautiful, often coloured, sporidia. These latter have either a smooth, warted, spinulose, or lacunose epispore, and, as will be seen from the figures in Tulasne's Monograph,[v] or those in the last volume of Corda's great work,[w] are attractive microscopical objects.

In some cases, it is not difficult to detect paraphyses, but in others they would seem to be entirely absent. A comparatively large number have been discovered and recorded in Great Britain,[x] but of those none are more suitable for study of general structure than the ordinary truffle of the markets.

The structure of the remaining Ascomycetes can be studied under two groups, _i.e._, the fleshy Ascomycetes, or, as they have been termed, the Discomycetes, and the hard, or carbonaceous Ascomycetes, sometimes called the Pyrenomycetes. Neither of these names gives an accurate idea of the distinctions between the two groups, in the former of which the discoid form is not universal, and the latter contains somewhat fleshy forms. But in the Discomycetes the hymenium soon becomes more or less exposed, and in the latter it is enclosed in a perithecium. The Discomycetes are of two kinds, the pileate and the cup-shaped. Of the pileate such a genus as _Gyromitra_ or _Helvella_ is, in a certain sense, a.n.a.logous to the Agarics amongst _Hymenomycetes_, with a superior instead of an inferior hymenium, and enclosed, not naked, spores. Again, _Geoglossum_ is somewhat a.n.a.logous to _Clavaria_. Amongst the cup-shaped, _Peziza_ is an Ascomycetous _Cyph.e.l.la_. But these are perhaps more fanciful than real a.n.a.logies.

Recently Boudier has examined one group of the cup-shaped Discomycetes, the _Ascobolei_, and, by making a somewhat free use of his Memoir,[y] we may arrive at a general idea of the structure in the cupulate Discomycetes. They present themselves at first under the form of a small rounded globule, and almost entirely cellular. This small globule, the commencement of the receptacle, is not long in increasing, preserving its rounded form up to the development of the asci. At this period, under the influence of the rapid growth of these organs, it soon produces at its summit a fissure of the external membrane, which becomes a more marked depression in the marginate species. The receptacle thus formed increases rapidly, becomes plane, more convex, or more or less undulated at the margin, if at all of large size.

Fixed to the place where it is generated by some more or less abundant mycelioid filaments, the receptacle becomes somewhat cup-shaped and either stipitate or sessile, composed of the receptacle proper and the hymenium.

[Ill.u.s.tration: FIG. 33.--Section of cup of _Ascobolus_. _a._ External cells. _b._ Secondary layer. _c._ Subhymenial tissue (Janczenski).]

The receptacle proper comprehends the subhymenial tissue, the parenchyma, and the external membrane. The subhymenial tissue is composed of small compact cells, forming generally a more coloured and dense stratum, the superior cells of which give rise to the asci and paraphyses. The parenchyma is seated beneath this, and is generally of interlaced filaments, of a looser consistency than the preceding, united by intermediate cellules. The external membrane, which envelopes the parenchyma, and limits the hymenium, differs from the preceding by the cells often being polyhedric, sometimes transverse, and united together, and sometimes separable. Externally it is sometimes smooth, and sometimes granular or hairy.

The hymenium is, however, the most, important part, consisting of (1) the paraphyses, (2) the asci, and sometimes (3) an investing mucilage.

The asci are always present, the paraphyses are sometimes rare, and the mucilage in many cases seems to be entirely wanting.

The paraphyses, which are formed at the first commencement of the receptacle, are at first very short, but soon elongate, and become wholly developed before the appearance of the asci. They are linear, sometimes branched and sometimes simple, often more or less thickened at their tips; almost always they contain within them some oleaginous granules, either coloured or colourless. Their special function seems still somewhat obscure, and Boudier suggests that they may be excitatory organs for the dehiscence of the asci. However this may be, some mycologists are of opinion that, at least in some of the Ascomycetes, the paraphyses are abortive asci, or, at any rate, that abortive asci mixed with the paraphyses cannot be distinguished from them.

The mucilage forms itself almost at the same time as the paraphyses, and previous to the formation of the asci. This substance appears as a colourless or yellowish mucilage, which envelopes the paraphyses and asci, and so covers the hymenium with a shining coat.

The asci appear first at the base of the paraphyses, under the form of oblong cells, filled with colourless protoplasm. By rapid growth, they soon attain a considerable size and fulness, the protoplasm being gradually absorbed by the sporidia, the first indication of which is always the central nucleus. The mucilage also partly disappears, and the asci, attaining their maturity, become quite distinct, each enclosing its sporidia. But before they take their complete growth they detach themselves from the subhymenial tissue, and being attenuated towards their base, are forced upwards by pressure of the younger asci, to, and in some instances beyond, the upper surface of the disc. This phenomenon commences during the night, and continues during the night and all the morning. It attains its height at mid-day, and it is then that the slightest breath of air, the slightest movement, suffices to cause dehiscence, which is generally followed by a scarcely perceptible contractile motion of the receptacle.

[Ill.u.s.tration: FIG. 34.--Asci, sporidia, and paraphyses of _Ascobolus_ (Boudier).]

There is manifestly a succession in formation and maturity of the asci in a receptacle. In the true _Ascobolei_, in which the sporidia are coloured, this may be more distinctly seen. At first some thin projecting points appear upon the disc, the next day they are more numerous, and become more and more so on following days, so as to render the disc almost covered with raised black or crystalline points;[z] these afterwards diminish day by day, until they ultimately cease. The asci, after separation from the subhymenial tissue, continue to lengthen, or it may be that their elasticity permits of extension, during expulsion. Boudier considers that an amount of elasticity is certain, because he has seen an ascus arrive at maturity, eject its spores, and then make a sharp and considerable movement of retraction, then the ascus returned again, immediately towards its previous limits, always with a reduction in the number of its contained sporidia.

The dehiscence of the asci takes place in the _Ascobolei_, in some species of _Peziza_, _Morch.e.l.la_, _Helvella_, and _Verpa_, by means of an apical operculum, and in other _Pezizae_, _Helotium_, _Geoglossum_, _Leotia_, _Mitrula_, &c., by a fissure of the ascus. This operculum may be the more readily seen when the ascus is coloured by a drop of tincture of iodine.

The sporidia are usually four or eight, or some multiple of that number, in each ascus, rarely four, most commonly eight. At a fixed time the protoplasm, which at first filled the asci, disappears or is absorbed in a mucilaginous matter, which occupies its place, in the midst of which is a small nucleus, which is the rudiment of the first spore; other spores are formed consecutively, and then the substance separates into as many sections as there are sporidia. From this period each sporidium seems to have a separate existence. All have a nucleus, which is scarcely visible, often slightly granular, but which is quite distinct from the oleaginous sporidioles so frequent amongst the Discomycetes, and which are sometimes called by the same name. The sporidia are at first a little smaller than when mature, and are surrounded by mucilage. After this period the sporidia lose their nebulous granulations, whilst still preserving their nucleus; their outlines are distinct, and, amongst the true _Ascobolei_, commence acquiring a rosy colour, the first intimation of maturity. This colour manifests itself rapidly, acc.u.mulating exclusively upon the epispore, which becomes of a deep rose, then violet, and finally violet blue, so deep as sometimes to appear quite black. There are some modifications in this coloration, since, in some species, it pa.s.ses from a vinous red to grey, then to black, or from rose-violet to brown.

The epispore acquires a waxy consistence by this pigmentation, so that it may be detached in granules. It is to this particular consistency of the epispore that the cracks so frequent in the coloured sporidia of _Ascobolus_ are due, through contraction of the epispore. As they approach maturity, the sporidia acc.u.mulate towards the apex of the asci, and finally escape in the manner already indicated.

In all essential particulars there is a great similarity in the structure of the other Discomycetes, especially in their reproductive system. In most of them coloured sporidia are rare. In some the receptacle is pileate, clavate, or inflated, whilst in _Stictis_ it is very much reduced, and in the lowest form of all, _Ascomyces_, it is entirely absent. In the _Phacidiacei_, the structure is very similar to that of the _Elvellacei_, whilst the _Hysteriacei_, with greater affinities with the latter, still tend towards the _Pyrenomycetes_ by the more h.o.r.n.y nature of the receptacle, and the greater tendency of the hymenium to remain closed, at least when dry. In some species of _Hysterium_, the sporidia are remarkably fine. M. Duby[AA] has subjected this group to examination, and M. Tulasne partly so.[AB]

SPHaeRIACEI.--In this group there is considerable variation, within certain limits. It contains an immense number of species, and these are daily being augmented. The general feature in all is the presence of a perithecium, which contains and encloses the hymenium, and at length opening by a pore or ostiolum at the apex. In some the perithecia are simple, in others compound; in some immersed in a stroma, in others free; in some fleshy or waxy, in others carbonaceous, and in others membranaceous. But in all there is this important difference from the Ascomycetes we have already had under consideration, that the hymenium is never exposed. The perithecium consists usually of an external layer of cellular structure, which is either smooth or hairy, usually blackish, and an internal stratum of less compact cells, which give rise to the hymenium.

[Ill.u.s.tration: FIG. 35.--Perithecium of _Sphaeria_ and Section.]

As in the _Discomycetes_, the hymenium consists of asci, paraphyses, and mucilage, but the whole forms a less compact and more gelatinous ma.s.s within the perithecium. The formation and growth of the asci and sporidia differ little from what we have described, and when mature the asci dehisce, and the sporidia alone are ejected from the ostiolum. We are not aware that operculate asci have yet been detected. It has been shown in some instances, and suspected in others, that certain moulds, formerly cla.s.sed with _Mucedines_ and _Dematiei_, especially in the genus _Helminthosporium_, bear the conidia of species of _Sphaeria_, so that this may be regarded as one form of fruit.

Perithecia, very similar externally to those of _Sphaeria_, but containing spores borne on slender pedicels and not enclosed in asci, have had their relations to certain species of _Sphaeria_ indicated, and these are no longer regarded so much as species of _Hendersonia_ or _Diplodia_ as the pycnidia of _Sphaeria_. Other and more minute perithecia, containing minute, slender stylospores in great numbers, formerly cla.s.sed with _Aposphaeria_, _Phoma_, &c., but are now recognized as spermogonia containing the spermatia of _Sphaeriae_. How these influence each other, when and under what circ.u.mstances the spermatia are instrumental in impregnation of the sporidia, is still matter of mystery. It is clear, however, that in all these conidia, macrospores, microspores, and some spermatia, or by whatever names they may be called, there exists a power of germination. Tulasne has indicated in some instances five or six forms of fruit as belonging to one fungus, of which the highest and most perfect condition is a species of _Sphaeria_.

[Ill.u.s.tration: FIG. 36.--_Uncinula adunca._]

PERISPORIACEI.--Except in the perithecia rupturing irregularly, and not dehiscing by a pore, some of the genera in this group differ little in structure from the _Sphaeriacei_. On the other hand, the _Erysiphei_ present important and very interesting features. They occur chiefly on the green parts of growing plants. At first there is a more or less profuse white mycelium.[AC] This gives rise to chains of conidia (_Oidium_), and afterwards small sphaeroid projections appear at certain points on the mycelium. These enlarge, take an orange colour, ultimately pa.s.sing into brown, and then nearly black.

Externally these perithecia are usually furnished with long, spreading, intertwined, or branching appendages, sometimes beautifully branched or hooked at their tips. In the interior of the receptacles, pear-shaped or ovate asci are formed in cl.u.s.ters, attached together at the base, and containing two or more hyaline sporidia. Other forms of fruit have also been observed on the same mycelium. In an exotic genus, _Meliola_, the fulcra, or appendages, as well as the mycelium, are black, otherwise it is very a.n.a.logous to such a genus of _Erysiphei_ as _Microsphaeria_. In _Chaetomium_, the perithecia bristle with rigid, dark-coloured hairs, and the sporidia are coloured. Our limits, however, will not permit of further elucidation of the complex and varied structure to be found amongst fungi.[AD]

[A] A curious case occurred some years since at Bury St. Edmunds, which may be mentioned here in connection with the development of these nodules. Two children had died under suspicious circ.u.mstances, and an examination of the body of the latter after exhumation was made, a report having arisen that the child died after eating mushrooms. As certain white nodules appeared on the inner surface of the intestines, it was at once hastily concluded that the spores of the mushroom had germinated, and that the nodules were infant mushrooms. This appeared to one of us so strange, that application was made for specimens, which were kindly forwarded, and a cursory glance was enough to convince us that they were not fungoid. An examination under the microscope further confirmed the diagnosis, and the application of nitric acid showed that the nodules were merely due to chalk mixture, which had been given to the child for the diarrhetic symptoms under which he succ.u.mbed.

[B] Ehrenberg compared the whole structure of an Agaric with that of a mould, the mycelium corresponding with the hyphasma, the stem and pileus with the flocci, and the hymenium with the fructifying branchlets. The comparison is no less ingenious than true, and gives a lively idea of the connection of the more n.o.ble with the more humble fungi.--_Ehrb. de Mycetogenesi._

[C] In _Paxillus involutus_ the hymenium may be readily torn off and unfolded.

[D] This was well delineated in "Flora Danica," plate 834, as observed in _Coprinus comatus_ as long ago as 1780.

[E] A. de Bary, "Morphologie und Physiologie der Pilze," in "Hofmeister's Handbuch," vol. ii. cap. 5, 1866, translated in "Grevillea," vol. i. p. 181.

[F] "Die Pollinarien und Spermatien von _Agaricus_," in "Botanische Zeitung," Feb. 29 and March 7, 1856.

[G] "Essai d'une Flore mycologique de la Region de Montpellier."

Paris, 1863.

[H] Hoffmann, "Botanische Zeitung," 1856, p. 139.

[I] Corda, "Icones Fungorum hucusque cognitorum," iii. p. 41. Prague, 1839.

[J] Cooke, M. C., "Anatomy of a Mushroom," in "Popular Science Review," vol. viii. p. 380.

[K] An attempt was made to show that, in _Agaricus melleus_, distinct asci were found, in a certain stage, on the gills or lamellae.

We have in vain examined the gills in various conditions, and could never detect anything of the kind. It is probable that the asci belonged to some species of _Hypomyces_, a genus of parasitic Sphaeriaceous fungi.

[L] It is not intended that the spores are always quaternate in _Agaricini_, though that number is constant in the more typical species. They sometimes exceed four, and are sometimes reduced to one.

[M] The species long known as _Hydnum gelatinosum_ was examined by Mr. F. Currey in 1860 (_Journ. Linn. Soc._), and he came to the conclusion that it was not a good _Hydnum_. Since then it has been made the type of a new genus (Hydnogloea B. and Br.

or, as called by Fries, in the new edition of "Epicrisis,"

_Tremellodon_, Pers. Myc. Eur.), and transferred to the _Tremellini_. Currey says, upon examining the fructification, he was surprised to find that, although in its external characters it was a perfect _Hydnum_, it bore the fruit of a _Tremella_. If one of the teeth be examined with the microscope, it will be seen to consist of threads bearing four-lobed sporoph.o.r.es, and spores exactly similar to _Tremella_. It will thus be seen, he adds, that the plant is exactly intermediate between _Hydnei_ and _Tremellini_, forming, as it were, a stepping-stone from one to the other.

[N] Tulasne, L. R. and C., "Observations on the Organization of the Tremellini," in "Ann. des Sci. Nat." 3^me ser. xix. (1853), pp.

193, &c.

[O] M. Leveille, in "Ann. des Sci. Nat." 2^me ser. viii. p. 328; 3^me ser. ix. p. 127; also Bonorden, "Handbuch der Mycologie," p.

151.

[P] Tulasne, in "Ann. des Sci. Nat." (loc. cit.) xix. pl. x. fig. 29.

Tulasne, "New Notes upon Tremellinous Fungi," in "Journ. Linn.

Soc." vol. xiii. (1871), p. 31.

[Q] Berkeley, M. J., "On the Fructification of Lycoperdon, Phallus, &c.," in "Ann. Nat. Hist." 1840, vol. iv. p. 158, pl. 5.

Berkeley, M. J., "Introduction Crypt. Bot." p. 346.

[R] Tulasne, L. R. and C., "Fungi Hypogaei." Paris. Berkeley and Broome, "British Hypogaeous Fungi," in "Ann. Nat. Hist." 1846, xviii. p. 74. Corda, "Icones Fungorum," vol. vi. pl. vii.

viii.

[S] Tulasne, "Sur le Genre _Secotium_," in "Ann. des Sci. Nat."

(1845), 3^me ser. vol. iv. p. 169, plate 9.