le cells, or
asci, mixed with linear thread-like barren cells, called paraphyses,
which are regarded by some authors as barren asci. These are placed
side by side in juxtaposition with the apex outwards. Each ascus
contains a definite number of sporidia, which are sometimes coloured.
When mature, the asci explode above, and the sporidia may be seen
escaping like a miniature cloud of smoke in the light of the mid-day
sun. The disc or surface of the hymenium is often brightly coloured in
the genus _Peziza_; tints of orange, red, and brown having the
predominance.

In _Phacidiacei_, the substance is hard and leathery, intermediate
between the fleshy _Elvellacei_ and the more horny of the _Sphaeriacei_.
The perithecia are either orbicular or elongated, and the hymenium soon
becomes exposed. In some instances, there is a close affinity with
the _Elvellacei_, the exposed hymenium being similar in structure,
but in all the disc is at first closed. In orbicular forms, the
fissure takes place in a stellate manner from the centre, and the
teeth are reflexed. In the _Hysteriacei_, where the perithecia are
elongated, the fissure takes place throughout their length. As a
rule, the sporidia are more elongated, more commonly septate, and more
usually coloured, than in _Elvellacei_. Only a few solitary instances
occur of individual species that are parasitic on living plants.

[Illustration: FIG. 42.--_Sphaeria aquila._]

In the _Sphaeriacei_, the substance of the stroma (when present) and of
the perithecia is variable, being between fleshy and waxy in
_Nectriei_, and tough, horny, sometimes brittle, in _Hypoxylon_. A
perithecium, or cell excavated in the stroma which fulfils the
functions of a perithecium, is always present. The hymenium lines the
inner walls of the perithecium, and forms a gelatinous nucleus,
consisting of asci and paraphyses. When fully mature, the asci are
ruptured and the sporidia escape by a pore which occupies the apex of
the perithecium. Sometimes the perithecia are solitary or scattered,
and sometimes gregarious, whilst in other instances they are closely
aggregated and immersed in a stroma of variable size and form.
Conidia, spermatia, pycnidia, &c., have been traced to and associated
with some species, but the history of others is still obscure. Many of
the coniomycetous forms grouped under the _Sphaeronemei_ are probably
conditions of the _Sphaeriacei_, as are also the _Melanconiei_, and
some of the _Hy