Fungi: Their Nature and Uses

by M. C. Cooke

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 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 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 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 which form 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 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.[] 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 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, analogous to the Agarics amongst Hymenomycetes, with a superior instead of an inferior hymenium, and enclosed, not naked, spores. Again, Geoglossum is somewhat analogous to Clavaria. Amongst the cup-shaped, Peziza is an Ascomycetous Cyphella. But these are perhaps more fanciful than real analogies.

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.

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.