scomycetes, 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 horny 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.

[Illustration: 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
mass 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 classed 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