some
species of _Stigmatea_ and _Dothidea_. Of the genus _Sphaeria_, a
considerable number are found on dung, now included by some authors
under _Sordaria_ and _Sporormia_, genera founded, as we think, on
insufficient characters. A limited number of species are parasitic on
lichens, and one species only is known to be aquatic.

[Illustration: FIG. 109.--_Torrubia militaris_ on pupa of a moth.]

We have thus rapidly, briefly, and casually indicated the habitats to
which the majority of the larger groups of fungi are attached,
regarding them from a systematic point of view. There is, however,
another aspect from which we might approach the subject, taking
the host or matrix, or in fact the habitat, as the basis, and
endeavouring to ascertain what species of fungi are to be found in
such positions. This has partly been done by M. Westendorp;[E] but
every year adds considerably to the number of species, and what might
have been moderately accurate twelve years since can scarcely be so
now. To carry this out fully a special work would be necessary, so
that we shall be content to indicate or suggest, by means of a few
illustrations, the forms of fungi, often widely distinct in
structure and character, to be found in the same locality.

The stems of herbaceous plants are favourite habitats for minute
fungi. The old stems of the common nettle, for example, perform the
office of host to about thirty species.[F] Of these about nine are
_Pezizae_, and there are as many sphaeriaceous fungi, whilst three
species of _Dendryphium_, besides other moulds, select this plant.
Some of these have not hitherto been detected growing on any other
stems, such as _Sphaeria urticae_ and _Lophiostoma sex-nucleatum_, to
which we might add _Peziza fusarioides_ and _Dendryphium griseum_.
These do not, however, include the whole of the fungi found on the
nettle, since others are parasitic upon its living green parts. Of
these may be named _AEcidium urticae_ and _Peronospora urticae_, as well
as two species described by Desmazieres as _Fusisporium urticae_ and
_Septoria urticae_. Hence it will be seen how large a number of fungi
may attach themselves to one herbaceous plant, sometimes whilst
living, but most extensively when dead. This is by no means a solitary
instance, but a type of what takes place in many others. If, on the
other hand, we select such a tree as the common lime, we shall find
that the leaves, twigs, branches, and wood bear, accor