28
PLANT DISEASES AND FUNGI.
to no remedy for everything which shall be "worth a guinea per
box." Morison's pills are not yet invented which shall cure apple
scab, potato rot, or vine mildew. Empirics may arise, but empiricism
will effect no cure, except by accident. As there is no royal road to
knowledge in general, so there is no royal road to knowledge in this
particular instance, and no universal cure. It must be borne in
mind that there are at least two classes of fungoid diseases, viz.,
those which are epiphytal, growing upon the plant from the outside,
and those which are endophytal, or developed from within the tissues
of the affected plant. Necessarily the means adopted for the cure
must have regard, first of all, to the one of the two classes to which
the fungus belongs. The epiphytal kinds are represented by our
ordinary vine mildew, by the hop mildew, by the mildew of peas,
by all those in which a web-like mycelium of delicate threads spreads
over the surface of the leaves, chokes up the pores, prevents the
ingress or egress of air, and suffocates the plant. In such diseases
the destruction of the fungus must be attempted in such a manner as
not to injure the host plant. This may be done by the application
of fungicides, and especially by the application of sulphur. It was
the discovery of this remedy which greatly mitigated the disease in
the hop and vine mildew, and is known to be the most beneficial in
any case of similar infection, but it is useless when applied to fungi
of the other class, which are endophytal, and must be treated in a
different manner. Another remarkable analogy here is presented in
the treatmeut of plants and animals. A short treatise by Dr. Valen-
tine Knaggs on "The Cure of Diphtheria by the Frequent Administra-
tion of Small Doses of Sulphur," affords this analogy. He says:
"More than five years ago my father employed sulphur with magical
effect in a case which was at that time regarded as desperate. The
severity of the symptoms were hourly increasing under carbolic and
other applications; but by the sulphur treatment, employed in the
manner I here advocate, the patient made a rapid recovery. Since
that time both my father and I have treated similarly seventy-two
cases, in all of which diphtheritic deposit was unmistakably and mark-
edly present. Though many of them were of a severe character,
some even with laryngeal complication, and accompanied by lividity
of skin, yet in not a single instance has a fatal termination occurred,
and in remarkably few of them have any of the ill effects which are
so apt to follow this complaint, even in the mildest and most transient
forms, resulted." Further on, and incidentally, he says: "Sulphur