th considerable force. When
a large _Peziza_ is observed for a time a whitish cloud will be seen
to rise suddenly from the surface of the disc, which is repeated again
and again whenever the specimen is moved. This cloud consists of
sporidia ejected simultaneously from several asci. Sometimes the
ejected sporidia lie like frost on the surface of the disc.
Theories have been devised to account for this sudden extrusion of the
sporidia, in _Ascobolus_, and a few species of _Peziza_, of the asci
also, the most feasible one being the successive growth of the
asci; contraction of the cup may also assist, as well as some other
less potent causes. It may be remarked here that the sporidia in
_Peziza_ and _Helotium_ are mostly colourless, whilst in _Ascobolus_
they pass through pink to violet, or dark brown, and the epispore,
which is of a waxy nature, becomes fissured in a more or less
reticulated manner.

[Illustration: FIG. 67.--Sporidium of _Ostreichnion Americanum_.]

The sporidia in _Hysterium_ proper are usually coloured, often
multiseptate, sometimes fenestrate, and occasionally of considerable
size. There is no evidence that the sporidia are ever excluded in the
same manner as in _Peziza_, the lips closing over the disc so much as
to prevent this. The diffusion of the sporidia probably depends on the
dissolution of the asci, and hence they will not be widely dispersed,
unless, perhaps, by the action of rain.

In _Tympanis_, asci of two kinds have been observed in some species;
one kind containing an indefinite number of very minute bodies
resembling spermatia, and the other octosporous, containing sporidia
of the usual type.

The _Sphaeriacei_ include an almost infinite variety in the form and
character of the sporidia. Some of these are indefinite in the number
contained in an ascus, although the majority are eight, and a few
less. In the genera _Torrubia_ and _Hypocrea_ the structure differs
somewhat from other groups, inasmuch as in the former the long
thread-like sporidia break up into short joints, and in the latter the
ascus contains sixteen subglobose or subquadrate sporidia. Other
species contain linear sporidia, which are often the length of the
ascus, and may either be simple or septate. In _Sphaeria ulnaspora_ the
sporidia are abruptly bent at the second joint. Shorter fusiform
sporidia are by no means uncommon, varying in the number of septa, and
in constriction at the joints in different species. Elli