ft ^ F
il '
the ease with which it may be confounded with the divided
walls of the cells and little fragments which project from
them when a section is made for the microscope. At times,
however, all difficulty ceases, and in potatoes affected with
the Mould which bears so great a part in the production
of the Potato murrain I have seen instances in which the
tissues were almost entirely replaced by the spawn of the
Fungus.
One peculiarity about the growth of Fungi is the tendency
which they have to assume a circular disposition, and that not
merely in cases where the spawn is perennial, hut where the
whole existence of the Fungus is confined to a few days or
weeks. A mass of spawn, however, it must he observed, does
not arise in general from a single spore, but from a collection
of spores, which spread in every direction and form a common
felt from whence the fruit rises. I will not enter upon the
question whether it is possible that several spores, after making
a common felt, may enter into the composition of the
same fruit. This is indeed asserted by Ehrenberg, but the
point is one of extreme delicacy, and requires much confirmation
before it can be received as an established fact. Nevertheless,
as the mass grows from a common centre, it is conceivable
enough that at a common distance from that centre
the spawn should be in a fit condition to produce fruit, and
that as it continues to spread, the same process should take
place again ; and that, in this way, a concentric arrangement
of the fruit should take place, as is the case in some Lichens ;
as, for example, in that formerly known under the name of
Lichen concentricus.* This disposition is especially evident
in some of the parasites which affect fruit, and in none more
so than in Oidium fructigenum, a Mould which is extremely
* Now Lecidea atro^alba.
common in autumn on pears, apples, and other fruit, and frequently
while yet hanging on the tree.
In the fields we see this tendency illustrated by the formation
of fairy rings, which have for a long time puzzled philosophers,
and are not without their difficulties now. These
rings are sometimes of very ancient date, and attain enormous
dimensions, so as to be distinctly visible on a hillside from a
considerable distance. I t is believed that they originate from
a single Fungus, whose growth renders the soil immediately
beneath unfit for its reproduction. The spawn, however,
spreads all round, and in the second year produces a crop,
whose spawn spreads again, the soil behind forbidding its
return in that direction. Thus the circle is continually increased,
and extends indefinitely till some cause intervenes to
destroy it. I f the spawn did not spread on all sides at first,
an arc of a circle only is produced. The manure arising from
the dead Fungi of the former years makes the grass peculiarly
vigorous around, so as to render the circle visible even
when there is no external appearance of the Fungus, and
the contrast is often the stronger from that behind being
killed by the old spawn. This mode of growth is far more
common than is supposed, and may be observed constantly in
our woods, where the spawn can spread only in the soil or
amongst the leaves and decaying fragments which cover it.
The rapidity with which spawn penetrates, and the depth
to which it enters, is often quite surprising. The most solid
timber, in a few months, when exposed to the weather and
in a damp situation favourable to the development of Fungi,
will sometimes show unequivocal traces of spawn. I have
seen, for instance, elm trunks which were perfectly sound
when felled, penetrated by the end of the second year with
spawn to within a few inches of the centre; and in this case