tato disease and its allies. A still larger number of
fungi are developed from decayed or decaying vegetable matter. These
are found in winter on dead leaves, twigs, branches, rotten wood, the
remains of herbaceous plants, and soil largely charged with
disintegrated vegetables. As soon as a plant begins to decay it
becomes the source of a new vegetation, which hastens its destruction,
and a new cycle of life commences. In these instances, whether
parasitic on living plants or developed on dead ones, the source is
still vegetable. But this is not always the case, so that it cannot be
predicated that fungi are wholly epiphytal. Some species are always
found on animal matter, leather, horn, bone, &c., and same affect such
unpromising substances as minerals, from which it would be supposed
that no nourishment could be obtained, not only hard gravel stones,
fragments of rock, but also metals, such as iron and lead, of which
more may be said when we come to treat of the habitats of fungi.
Although in general terms fungi may be described as "hysterophytal or
epiphytal mycetals deriving nourishment by means of a mycelium from
the matrix,"[G] there are exceptions to this rule with which the
majority accord.

Of the fungi found on animal substances, none are more extraordinary
than those species which attack insects. The white mould which in
autumn proves so destructive to the common house-fly may for the
present be omitted, as it is probably a condition of one of the
_Saprolegniei_, which some authors include with fungi, and others with
algae. Wasps, spiders, moths, and butterflies become enveloped in a
kind of mould named _Isaria_, which constitutes the conidia of
_Torrubia_, a genus of club-shaped _Sphaeriae_ afterwards developed.
Some species of _Isaria_ and _Torrubia_ also affect the larvae and pupae
of moths and butterflies, converting the whole interior into a mass of
mycelium, and fructifying in a clavate head. It has been subject for
discussion whether in such instances the fungus commenced its
development during the life of the insect, and thus hastened its
death, or whether it resulted after death, and was subsequent to the
commencement of decay.[H] The position in which certain large moths
are found standing on leaves when infested with _Isaria_ resembles so
closely that of the house-fly when succumbing to _Sporendonema Muscae_,
would lead to the conclusion that certainly in some cases the insect
was attacked by the