it must be remembered that vegetation goes on in the trunk
for nearly a twelvemonth before any Fungi can establish
themselves. The growth of Dry-rot is unfortunately familiar
to all, and instances occur in which its spawn not only enters
the wood, hut penetrates solid structures of brick.
When spawn has once taken possession of a spot favourable
to its growth, it is astonishing what an immense resistance it
will sometimes overcome. Large flagstones, for instance, are
sometimes raised by Mushrooms, and even tender species
like the Coprini (Plate 13, fig. 1) will sometimes resist a considerable
pressure.
Where the spawn of Fungi has high powers of vegetation, but
no possibility of getting access to the external air, it assumes
peculiar forms which are sometimes extremely puzzling. In the
middle of a solid trunk, for instance, it forms black plates,—■
as in the case of the common scaly Sapball, Polyporus squamosus,
and several of the more solid Sphæriacei,—while, when
running between the hark and wood, it assumes the form of a
flat, anastomosing, black seaweed, rather than of a Fungus, in
which cases it is known under the name of Rhizomorpha sub-
corticalis, etc. This form is assumed by the spawn of various
Polypori and Xylariæ, and in some cases the condition to a
certain extent seems to be almost normal. The absence of
light, too, impedes the proper development of Fungi, and
hence a variety of forms occur, very few of which perfect
their fruit. I have even found a Coprinus, which grew down
from the interior of the roof of a hovel, though perfect in
other respects, absolutely devoid of fruit.
Spawn, as said above, may exist for years without producing
fruit, and it is probable that this is equally the case
whether it runs through soil or decaying substances, or
amongst living tissues, whether without or within their walls.
Wheat Mildew, for instance, often arrives at a certain stage
of growth without perfecting its fruit, a fact which sufficiently
accounts for the apparently sudden appearance which
it makes in seasons favourable to its full development amongst
our crops.
As regards the growth of individual Fungi, it takes place
essentially in a direction from the centre to the circumference,
or, in other words, it is centrifugal. Hence a Polyporus, such
as P. fraxineus, involves every stick and blade of grass in its
way as it increases in diameter. The mode of growth is admirably
illustrated by a section of Polyporus hispidus, so
common on apple-trees, in which the threads of which it is
composed are seen to radiate in one direction towards the
pileus, where their free ends form the hispid fascicles on the
surface, and in another direction towards the hymenium,
where they form the walls of the tubes and sporophores. I t
is not indeed intimated that no growth takes place in any
other direction, but that the main direction is centrifugal.
. Fungi are in general of short duration, hut some go on
increasing for years. Polyporus fraxineus, though only a few
inches across, the first year, attains at length a breadth of as
many feet. Some of the stipitate Polypori scarcely attain
their full characters till the second year, and a few even of the
softer species, if they get through the winter, sprout again
from the portion of tissue which remains sound. In such
case, though at first the nutriment was derived from the
matrix, by means of the spawn which performs the functions
of roots, life is carried on by the absorption of surrounding
moisture, and perhaps partly at the expense of the dead
Fungi. Even some Agarics, as A. fusipes (Plate 5, fig- 5),
seem sometimes to sprout from the decayed stumps of the
previous year, without any fresh mycelium.