Several species of the genus _Nectria_, with blood-red perithecia, are found as dangerous parasites, especially _N. ditissima_, which causes “Canker” in the Beech, Ash, and Apple, etc.; _N. cucurbitula_, which appears on Pine-trees, and _N. cinnabarina_ (Fig. 117), whose conidial form was formerly named _Tubercularia vulgaris_.--_Polystigma rubrum_ forms shining red spots on the green leaves of _Prunus_-species.--_Epichloë typhina_ is parasitic on the sheaths of Grasses, on which it first forms a white conidial-layer, later on a yellow layer of perithecia.--_Cordyceps_ (Chrysalis Fungus, Figs. 118, 119) lives in and destroys insects, and after compassing their death produces the club-formed, generally yellow, stromata, one part of which bears conidia (_Isaria_) and another perithecia. _C. militaris_ (Fig. 118) on the chrysalides and caterpillars of moths, is the most common. The so-called _Botrytis bassiana_, which produces the disease known by the name of “Muscardine,” in silkworms, is probably a conidial form belonging to _Cordyceps_. [Illustration: FIG. 118.--_Cordyceps militaris._ I Stromata with conidiophores (_Isaria farinosa_). II A larva, with stromata, bearing perithecia. III A spore.] [Illustration: FIG. 119.--_Cordyceps robertii_ on the larva of _Hepialus virescens_: _a_ stalk of stroma; _b_ perithecia.] Sub-Family 2. =Sphæriales.= To this sub-family belong the majority of the Pyrenomycetes. The perithecia are of a _firm consistence_ (tough, leathery, woody or carbonaceous), and of a _dark_ colour. Their _covering_ is _quite distinct from the stroma_ when this structure is present. The stromata are sometimes very large, and may be either cushion-like, crustaceous, upright and club-like, or branched bodies. In general, small, inconspicuous Fungi, living on dead vegetable matter, sometimes parasites. Free conidiophores and conidiocarps are known in many species, and in several, chlamydospore-like forms of reproduction. Orders 3–18 constitute the Sphæriaceæ of older systematists. [Illustration: FIG. 120.--_Strickeria obducens_: _a_ a portion of an Ash-branch with the bark partly thrown off; on the wood are numerous black perithecia (× 20); _b_ longitudinal section through a perithecium; _c_ a spore; _d_ longitudinal section through a pycnidium whose ascospores are being ejected; _e_ portion of the same, with hyphæ and spores.] Order 1. =Sordariaceæ.=--Fungi living on dung with fragile perithecia, either aerial or buried in the substratum. The dark brown or black spores have either a mucilaginous envelope (_Sordaria_, etc.) or mucilaginous appendages (_Podospora_), by means of which their expulsion and distribution are promoted. Order 2. =Chætomiaceæ.= Perithecia fragile, free, bearing on the summit a tuft of hairs. _Chætomium_, on decaying vegetable matter.