[Footnote 1: Communicated to the _Medical Times_ by Sir James Paget.]
An essay by Dr. Beijerinck, on the contagion of the gum disease in
plants, lately published by the Royal Academy of Sciences at
Amsterdam, contains some useful facts. The gum disease (_gummosis,
gum-flux)_ is only too well known to all who grow peaches, apricots,
plums, cherries, or other stone fruits. A similar disease produces gum
arabic, gum tragacanth, and probably many resins and gum resins. It
shows itself openly in the exudation of thick and sticky or hard and
dry lumps of gum, which cling on branches of any of these trees where
they have been cracked or wounded through the bark. Dr. Beijerinck was
induced to make experimental inoculations of the gum disease by
suspicions that, like some others observed in plants, it was due to
bacteria. He ascertained that it is in a high degree contagious, and
can easily be produced by inserting the gum under the edge of a wound
through the bark of any of the trees above named. The observation that
heated or long boiled pieces of gum lose their contagious property
made it most probable that a living organism was concerned in the
contagions; and he then found that only those pieces of the gum
conveyed contagion in which, whether with or without bacteria, there
were spores of a relatively highly organized fungus, belonging to the
class of Ascomycetes; and that these spores, inserted by themselves
under the bark, produced the same pathological changes as did the
pieces of gum. The fungus thus detected, was examined by Professor
Oudemans, who ascertained it to be a new species of Coryneum, and has
named it _Coryneum Beijerincki_. The inoculation experiments are best
made by means of incisions through the bark of young branches of
healthy peach trees or cherry trees, and by slightly raising the cut
edge of the bark and putting under it little bits of gum from a
diseased tree of the same kind. In nearly every instance these wounds
become the seats of acute gum disease, while similar wounds in the
same or other branches of the same tree, into which no gum is
inserted, remain healthy, unless, by chance, gum be washed into them
during rain. The inoculation fails only when the inserted pieces of
gum contain no Coryneum. By similar inoculations similar diseases can
be produced in plum, almond, and apricot trees, and with the gum of
any one of these trees any other can be infected; but of many other
substances which Beijerinck tried, not one produced any similar
disease. The inoculation with the gum is commonly followed by the
death of more or less of the adjacent structures; first of the bark,
then of the wood. Small branches or leaf stalks thus infected in
winter, or in many places at the same time, may be completely killed;
but, in the more instructive experiments the first symptom of the gum
disease is the appearance of a beautiful red color around the wound.
It comes out in spots like those which often appear spontaneously on
the green young branches of peach trees that have the gum disease; and
in these spots it is usual to find Coryneum stromata or mycelium
filaments. The color is due to the formation of a red pigment in one
or more of the layers of the cells of the bark. But in its further
progress the disease extends beyond the parts at which the Coryneum or
any structures derived from it can be found; and this extension,
Beijerinck believes, is due to the production of a fluid of the nature
of a ferment, produced by the Coryneum, and penetrating the adjacent
structures. This, acting on the cell walls, the starch granules, and
other constituents of the cells, transforms them into gum, and even
changes into gum the Coryneum itself, reminding the observer of the
self-digestion of a stomach.
In the cells of the cambium, the same fluid penetrating unites with
the protoplasm, and so alters it that the cells produced from it form,
not good normal wood, but a morbid parenchymatous structure. The cells
of this parenchyma, well known among the features of gum disease, are
cubical or polyhedral, thin walled, and rich in protoplasm. This, in
its turn, is transformed into gum, such as fills the gum channels and
other cavities found in wood, and sometimes regarded as gum glands.
And from this also the new ferment fluid constantly produced, and
tracking along the tissues of the branches, conveys the Coryneum
infection beyond the places in which its mycelium can be found.
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