This sub-class embraces the most highly developed Fungi, with large
“fruit-bodies,” which in ordinary language we shortly term Funguses,
Toadstools, or Mushrooms.
They have no sporangia, but reproduce only by means of basidiospores,
conidia, chlamydospores and oidia. The chief characteristic of this
sub-class is the _basidium_ (Fig. 145), _i.e._ the conidiophore, which
has a distinctive form, and bears a definite number (generally 4) of
characteristically shaped conidia (basidiospores, Fig. 145 _c_, _d_,
_e_).
[Illustration: FIG. 145.--Development of spores in _Corticium_.]
The summit of each basidium is produced generally into four conical
points (_sterigmata_, Fig. 145 _b_), from each of which a basidiospore
is abstricted. The basidia may be classified into three principal
groups, each of which accompanies a distinctive conidiophore: 1,
the long, filamentous, _transversely divided_ basidia, with lateral
sterigmata and spores, found in the Uredinaceæ (Figs. 146 _D_, 153),
Auriculariaceæ (Fig. 160 _B_), and Pilacraceæ; 2, the spherical,
_longitudinally divided_ basidia of the Tremellaceæ (Figs. 160 _C d_;
161 iii. iv.); and 3, the ovoid, or cylindrical, _undivided_ basidia of
the Autobasidiomycetes (Figs. 145, 163, etc.); the two last have apical
sterigmata and spores.
The first two groups are the septate basidia (_protobasidia_),
of the _Protobasidiomycetes_; while the unseptate basidia
(autobasidia) of the _Autobasidiomycetes_ are the third group.
On the formation of the basidiospores, the nucleus of the
basidium divides into four nuclei, each of which is transferred
to a spore.
In addition to the basidia, _simple conidiophores_ are also found.
In the Protobasidiomycetes, the simple conidia are very generally
found as accessory methods of reproduction in conjunction with the
basidiospores; but less frequently in the Autobasidiomycetes, _e.g._
among the Dacryomycetes, Tomentellaceæ, _Heterobasidion annosum_.
The simple conidiophores vary in size, and in the number and
shape of the conidia; they, however, resemble the basidia,
and are doubtless an early stage in the development of the
definitely formed basidia.
Finally, well-defined _chlamydospores_, formed in various ways, appear
in the Basidiomycetes as supplementary reproductive bodies (compare p.
90). Among the Protobasidiomycetes, chlamydospores are at present only
found among the Uredinaceæ, but in various forms; in the majority of
families of the Autobasidiomycetes _oidia_ frequently occur (Fig. 162),
but genuine chlamydospores seldom.
In the same species several of the known forms of reproduction may be
distinguished.
The _mycelium_ is generally composed of white, branched strands,
consisting of numerous felted hyphæ; in some, sclerotia are found.--The
great majority are saprophytes; some (particularly all the Uredinaceæ),
are parasites.