22 PLANT DISEASES AND FUNGI.
and destroyed. Upon inquiry it was found that all the plants raised
by the gardener's friend were also diseased in the same manner. The
only inference to be derived from these facts is that the disease was
latent in the seeds of the diseased plants, and that it was a clear case
of hereditary transmission. His own plants, raised from clean seed,
showed no trace of disease, although growing in close proximity to
diseased plants.
Another instance may be cited in support of this view. "Some
remarkable phenomena occurred in a garden near London, where
all the plants of Pyracantha, arising from particular seed, were more
or less completely destroyed by the same species of Fusicladium
which injures the pear trees. [The cause of the American "apple
scab."] The plants were raised from Russian seeds, about four or
five years previously. They first appeared to be blighted in the
year preceding this report, but inconsiderably. In the following
year they were nearly all killed. The old shoots were black with the
spores, the leaves crumpled and withered, and the late shoots and
leaves were about to break out as their predecessors. The seedling
bushes were growing in heavy land, well drained, but the disease
was confined to them. Old bushes of Pyracantha in the same
places were perfectly clean." 4
Not only are plant diseases hereditary, as are some diseases in
the human subject, but they appear to be analogous also in their
epidemical character. Many years since the Rev. M. J. Berkeley
alluded to this subject in the following terms :—"There is some-
thing extremely capricious in the attacks of these diseases amongst
plants, exactly as is the case with infectious maladies amongst our-
selves. One is taken and another left without our being able to
account for it; nor is it probable that we shall ever penetrate these
mysteries, which baffle all our efforts, and remind us of our true
position in the scale of intelligent beings. A perennial plant, or
tree, once attacked by parasites, seldom gets perfectly free from the
disease, and there may be a greater analogy in the peculiar liability
of certain constitutions to the recurrence of such maladies as
influenza, than, in fact, in the present state of our knowledge as
to the cause of disease we should be willing to allow."
The manner in which some of the most notable of fungus
diseases have appeared affords remarkable coincidences with the
spread of such human epidemics as cholera and influenza. The
4 "Gardener's Chronicle," October 28th, 1848.