ed, being free, erect,
and bearing the sporangia at the tips of the thread, or branches. Some of
the species bear great external resemblance to _Mucedines_ until the
fruit is examined, when the fructifying heads, commonly globose or ovate,
are found to be delicate transparent vesicles, enclosing a large number
of minute sporidia; when mature, the sporangia burst and the sporidia
are set free. In some species, it has long been known that a sort of
conjugation takes place between opposite threads, which results in the
formation of a sporangium.[Q] None of these species are destructive to
vegetation, appearing only upon decaying, and not upon living, plants.
A state approaching putrescence seems to be essential to their vigorous
development. The following characters may be compared with those of
the family preceding it:--

_Filamentous, threads free or only slightly felted, bearing vesicles,
which contain indefinite sporidia_ = PHYSOMYCETES.

[Illustration: FIG. 41.--_Mucor caninus._]

In the last family, the _Ascomycetes_, we shall meet with a very great
variety of forms, all agreeing in producing sporidia contained in
certain cells called asci, which are produced from the hymenium. In
some of these, the asci are evanescent, but in the greater number are
permanent. In _Onygenei_, the receptacle is either club-shaped or
somewhat globose, and the peridium is filled with branched threads,
which produce asci of a very evanescent character, leaving the
pulverulent sporidia to fill the central cavity. The species are all
small, and singular for their habit of affecting animal substances,
otherwise they are of little importance. The _Perisporiacei_, on the
other hand, are very destructive of vegetation, being produced, in the
majority of cases, on the green parts of growing plants. To this order
the hop mildew, rose mildew, and pea mildew belong. The mycelium is
often very much developed, and in the case of the maple, pea, hop, and
some others, it covers the parts attacked with a thick white coating,
so that from a distance the leaves appear to have been whitewashed.
Seated on the mycelium, at the first as little orange points, are the
perithecia, which enlarge and become nearly black. In some species,
very elegant whitish appendages radiate from the sides of the
perithecia, the variations in which aid in the discrimination of
species. The perithecia contain pear-shaped asci, which spring from
the base and enclose a definite