MYCOMYCETES. Septate vegetative mycelium. No sexual including the reproduction—as a general rule. Asexual conidia Sub-classes and other forms of spores. In the Ascomycetes ASCOMYCETES and the spores are found in characteristic BASIDIOMYCETES. club-shaped cases or asci; in the Basidiomycetes the spores are borne on special branches from swollen cells known as _basidia_. The sporophore or spore-bearing body in this group may attain a considerable size (e.g. _Agaricus_, _Polyporus_, &c.) and exhibit a distinct internal differentiation. Before describing a few examples of fossil fungi, it is important to consider the general question of their manner of occurrence and determination. Considering the small size and delicate nature of most fungi, it is not surprising that we have but few satisfactory records of well-defined fossil forms. The large leathery sporophores of _Polyporus_ and other genera of the Basidiomycetes, which are familiar objects as yellow or brown brackets projecting from the trunks of diseased forest trees, have been found in a fairly perfect condition in the Cambridgeshire peat-beds, and examples have been described also by continental writers[405]. As a general rule, however, we have to depend on the chance mineralisation or petrifaction of the hyphae of a fungus-mycelium which has invaded the living or dead tissues of some higher plant. In the literature on fossil plants there are numerous recorded species of fungi founded on dark coloured spots and blotches on the impression of a leaf. Most of such records are worthless; the external features being usually too imperfect to allow of accurate identification. The occurrence of recent fungi as discolourations on leaves is exceedingly common, and the characteristic _perithecia_ or compact and more or less spherical cases enclosing a group of sporangia in certain Ascomycetous species, might be readily preserved in a fossil condition. [Sidenote: ASCOMYCETES.]