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Pyrenomycetes (From pyren a kernel or stone)

(from pyren, a kernel or stone of fruit, and mykes, a Fungus). A very large group of Fungi, so named because they produce, in the processes of reproduction, small, hard, dark bodies (perithecia and pycnidia), in which certain forms of spores are protected. The Pyrenomycetes from one of three families, into which a very large order of Fungi, called Ascomycetes, is divided. This order is characterised by the mode of origin of a form of spore, regarded as the most highly developed of the various kinds produced in them. These spores are produced from a portion of the protoplasm, or living substance, contained in certain long, cylindrical, thin-walled cells, called asci. In each ascus there are usually eight spores formed, but the number varies, in different Fungi, from two to an indefinite number in each, though constant in each species. In most Ascomycetous Fungi, the asci grow crowded together, either alone or intermixed with slender filaments (paraphyses) and, in most, these groups of asci are surrounded with an outer coating of hyphae, united so as to simulate true parenchyma. In one group--the Discomycetes--this protecting tissue merely forms a saucer or disk, or a club, on which the asci stand (e.g., in Peziza), and the surface bearing the asci is exposed. In a few, e.g., Exoascus Pruni (see remarks on FUNGI, under Plum), the asci stand isolated and exposed, and not on any special area of the surface. In the Pyrenomycetes, including among them the Perisporacei, the protecting tissue forms a continuous sphere or flask-shaped perithecium, which entirely incloses the asci with the spores in them, and which, as in the Perisporiaceae, may be entirely closed, but far more generally opens by a pore or slit on its upper surface, or at the end of a more or less elongated neck. As a rule, there are many asci in each perithecium; but in a few species they may be few, or even reduced to a single ascus, as in Podosphaera (see PLUM FUNGI). Both in Discomycetes and in simple Pyrenomycetes, the development of the asci and spores has been traced to a union of male and female organs, and the protecting layers have been traced to branches developed from the mycelium after the female cell is fertilised.

The Pyrenomycetes live on every kind of food--on dead wood and leaves, on dead animal matter, on excrements, on the soil, and on living plants and animals; in this latter case, they are true parasites. Some of them prove hurtful to cultivated plants. An account of the more important structural characters of the Erisypheae, and of the injuries they inflict, will be found under the headings Mildew and Oidium. The restricted, or true, Pyrenomycetes differ from the Perisporiaceae (of which the Erisypheae form the section of most importance to gardeners) in the perithecium opening by a pore or a slit, and in the mycelium being not superficial, but sunk among the food, whether that is dead, or a living plant or animal. Hence, the mycelium is entirely concealed; and the parts which attract our notice are, in most cases, only the reproductive organs. There are several kinds of spores produced, as has been mentioned under Pleospora. The ascospores, or those contained in the asci, may be round, elliptical, or thread-like, transparent or brown, undivided, or divided by one, two, three, or many septa. In this latter case, the spores often seem very complex in their structure, being built up of many cells. The perithecia vary considerably in texture, whether nearly membranous, carbonaceous, or fleshy (Nectriaceae), and in form of orifice, whether a simple slit (in Hysteriacei), or a pore (Pleospora), or with thickened lips (Lophiostomacei). In some, the perithecia are scattered (Pleospora); in others, they are crowded together on specially modified parts of the Fungus (in Xylaria, Claviceps, &c.), or are sunk in the mycelium, in a mass called a "stroma." Besides the perithecia with ascospores, other structures, called pycnidia, much like perithecia in external appearance, are developed; and in them are contained spores, often much like those contained in the asci, e.g., in Cucurbitaria Laburni, where both are multicellular and brown, but, perhaps, more often very different from them in appearance, e.g., in Pleospora herbarum, in which the ascospores are multicellular and brown, and the pycnidio-spores are unicellular, transparent, and very much smaller (see Pleospora). The pycnidia have been named Phoma herbarum. Pycnidia are, in most cases, smaller and thinner-walled than the perithecia; but they vary in these respects, and also in being solitary in some groups, and crowded together in others. Occasionally, they are sunk in a stroma. They usually occur on the mycelium before the perithecia are formed, but may be associated with the latter. In the pycnidia, the spores are produced on the tips of branches, not in asci; but pycnidiospores are occasionally found in the same receptacle with ascospores.

Other modes of spore formation occur in many species (see Pleospora), resulting in the formation of conidia on the tips of branches that rise from the mycelium creeping on the surface of the body in which the Fungus is growing. These conidiophores, or conidia-bearers, are very various in form and modes of branching, and in the structure and form of their spores. In some cases, they are so associated with the more perfect stages of the Fungi that there is little difficulty in recognising their relationships; e.g., the very common Tubercularia vulgaris on dead branches is always followed by Nectria cinnabarina in such a manner as to indicate clearly their being states of the same Fungus. But the greater number of conidiophorous Fungi have not yet been referred as earlier stages to higher forms, though careful observations will almost certainly result in their being so, and will free the study of microscopic Fungi from a vast amount of doubt, and from multitudes of so-called species. In the meantime, in the imperfect state of our knowledge of these plants, it is found expedient to retain them in the group called Hyphomycetes, even though they are thus associated with Peronospora, and with other forms not closely related to them. Still another mode of reproduction in some is by means of Sclerotia, or hard masses of mycelium (see Sclerotia). It has been necessary to enter thus fully upon the account of the modes of reproduction observed in the Pyrenomycetes, since it is these alone that afford material for distinguishing the various genera and species, the mycelium not yielding characters that can be relied on for genera, or even families, much less for species. For an account of the injuries inflicted on cultivated plants by the Erisypheae among Perisporiacei, see Mildew and Oidium. Among the restricted Pyrenomycetes, a good many species are parasitic upon living plants; and several of these are injurious to field or to garden produce. Some of them are hurtful in the early stages of their growth, the perithecia being formed only after the death of the tissues on which they feed. Others only weaken the host-plants, and are to be found in all their stages upon living tissues of these plants. Some have already been referred to under the headings Pleospora and Plum (FUNGI). Among the most injurious forms may be mentioned one very hurtful to grasses that are grown for seed, viz., the Ergot (Claviceps purpurea), which, however, does so little harm to gardeners as to require no special notice here.