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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