purpose. The
form of the threads, and the mode of attachment of the spores, is far
more variable amongst the _Mucedines_ than the form of the spores, but
the latter are in all instances so slightly attached to their supports
as to be dissevered by the least motion. This aids also in the
diffusion of the spores through the atmosphere.

[Illustration: FIG. 63.--Spores of _Helicocoryne_.]

SPORANGIA are produced in the _Physomycetes_ usually on the tips or
branches of delicate threads, and these when mature dehisce and set
free the minute sporidia. These are so small and uniform in their
character that they require but a passing mention. The method of
diffusion agrees much with that of the _Mucedines_, the walls of the
sporangia being usually so thin and delicate as to be easily ruptured.
Other modes of fructification prevail in some species by the
production of cysts, which are the result of conjugation of the
threads. These bodies are for the most part furnished with thicker and
more resistant walls, and the diffusion of their contents will be
regulated by other circumstances than those which influence the
dispersion of the minute sporidia from the terminal cysts. Probably
they are more perennial in their character, and are assimilated more
to the oogonia of _Cystopus_ and _Peronospora_, being rather of the
nature of resting spores, inasmuch as the same threads usually bear
the terminal fruits.

[Illustration: FIG. 64.--Sporidium of _Genea verrucosa_.]

[Illustration: FIG. 65.--Alveolate sporidium of _Tuber_.]

THECASPORES is a term which may be applied generally to all sporidia
produced in asci, but these are in turn so innumerable and variable
that it will be necessary to treat of some of the groups individually.
The _Thecaspores_, for instance, of the _Tuberacei_ offer several
features whereby they may be distinguished from other thecaspores. The
asci in which these sporidia are generated mostly partake of a broadly
saccate, ovate form. The number of sporidia contained in an individual
ascus is usually less than in the majority of the _Ascomycetes_, and
the sporidia approximate more nearly to the globose form. Usually,
also, they are comparatively large. Many have been figured by Corda[C]
and Tulasne.[D] Three types of spores may be said to prevail in the
_Tuberacei_: the smooth spored, the warted or spinulose, and the
areolate. The first of these may be represented by the _Stephensia
bombycina_, in which the gl