26
PLANT DISEASES AND FUNGI.
"The attacked vines varied somewhat in their appearance, but
generally there is a decay of the stem in proximity to the root, and
then the whole plant wilts and fails to grow. Sometimes one or
more leaves will fall to the ground, and rot away, before the balance
of the plant is seemingly affected."
Dr. Byron Halsted reports8 that "a microscopical examination
of the decaying stems, leaves, and fruit showed that the decom-
posing tissues were teeming with bacteria. Inoculations of healthy
fruits were made in the usual way, taking the germs from the centre
of freshly-decaying cucumbers. It was found that, with no other
fungus present, these germs were abundantly able to introduce a
rapid decay into cucumbers, melons, and squashes. Cucumbers
seem to be the favourite, and in them the decay is the most rapid.
It will run from one end to the other, through the succulent centre
of a four-inch fruit, in a single day.
"The next step in the study was the application of these germs
to healthy plants in the field. When the inoculation was made near
the end of a vine, the latter rotted away in from three to four days,
and when nearer the base a longer time was required; but in all
cases an ulcer was formed, which spread more or less rapidly,
depending upon the tissue infected. In old stems the decay was almost
entirely internal, and did not show much until the disease had spread
through the pith to some distant soft parts. A medicine dropper
was employed to place a charge in the middle of several petioles of
large squash leaves. Upon the next visit, twenty-four hours after, all
such leaves had fallen to the ground, and the portion of the petioles
below the point of inoculation, six or more inches, in some cases,
were thoroughly decayed. In short, the bacterial disease first found
in the cucumber, and afterwards propagated from fruit to fruit in
the laboratory, as also upon cut stems and petioles, is readily
transmitted to vigorous living vines of the cucumber and squash
in the field."
Sixteen seeds of squash were divided, and eight planted in a pot
covered with a bell glass, watered with pure water, whilst eight in
another pot were watered from the first with the juice of a
cucumber which had decayed with bacteria. The first eight seeds
germinated quickly, producing large, deep green plants, while in the
other pot only two plants appeared above ground, and they were
of a dwarfed, sickly-yellow colour, and did not continue to grow.
8 "Botanical Gazette," Nov., 1891.