Oxford Democrat. [volume] (Paris, Me.) 1833-1933, 1877-05-15
The Black Knot.

There are many things IN nature SEEM
ingly so insignifc cant that we consider
them unworthy our notice; yet they have
the power of doing us great benefit or
harm according to their habit. The mold
upon bread, cheese, and on most other
neglected vegetable matter, is well known
TO be a plant growth of low order. It's
4 fungus, and of the same nature as our
common mushrooms. The potato disease,
which is causing so much anxiety in Eng
land and on the continent Of Europe, Is
also the result of fungous growth
These plants are now receiving consider
able study from b0tanists on account Of
both their practical and their Scientific
interest. In this country, and peculiar
to it, the black kont, as it Is called. on
plum and cherry trees has recently been
proven to be another fungus. DR.. w. ;.
Farlow,o of Harvard University has presen-
ted, in the Bulletin Of the BusSey Insti-
tuition, a most important paper rs the
result Of his researches on this subject.
The black, warty excrescenceS on plum
trees and on all kinds Of wild and cult
yatel cherries have been noticed by every
one from early time, and have long been
the bane Of fruit growers. For the most
part. these have been attributed to the
work of insects, and this has not been
without considerable shadow OF reason.
Insects are net untrequently found there,
and in old knots insects or their remains
are generally found The curculio often
pierces the knot in its young state, and
deposits within it Its eggs, which soon
hatch out. The young live in the knot,
and may BE found there IL the various
stages Of their development. Insects also
Of different species have been found with
in these knots. But it is now conclusive
iy demonstrated that the unSighty knots
are not Of insect origin. Though till
very recently, the subject has been almost
entirely neglected by bOtanists. it now
seems certain that they have determined
its true character.
The knots are not like gals, made by
a known insect and when young they
are most frequently entirely devoid OF
insects. Again, the fact that the insects
are not all OF one species, and the very
same arc also found on trees which are
never afflicted with knots, would be quite
conclusive against this assumption. On
the other hand, the knot has never been
found without the presence OF the specific
fungus lspharia morbosa), which Is now
accepted as It's origin and this fungus Is
not known 10 exist except in connection
with the knot. The mycelia threads, how
ever Of the fungus are found in the slight
ly swollen stem long before any real SEM
bIance to knot has appeared but the
growth OF these may be traced till the
knot has attained its full size, and the
fungus has shown all H. phases Of life.
DR.. Farlow has considered the life history
Of the fungus. whether the disease Is the
same on plum and cherry trees, and the
means Of preventing It's ravages. The
knots vary in size from few lines TO sew
eral inches in length, aud average about
two inches in circumference. They sell
dom entirely surround the branch, and
often cause it TO bend or twist into un-
slightly shapes. The vegetative portion
first appears in the form OF very minute
threads ,myeelluml, twisted together and
extending from the cambium-or inner
layer Of the bark towards the outer por-
ton Of the stem. The fungus first reach
es the cambium either by the germina-
ton Of spores on the surface Of the
branch, or by the mycelium proceeding
from a neighboring knot" Hence the
professor concludes that the growing lay
er Of tissue Is where the fungus common
ees Its work Of destruction.
During the growing stages of the knot
which continue TO the Towering time Of
its victim-it Is of a greenish color and
solid or PUPPY throughout When it has
attained its maturity, it turns black and
in the winter it often becomes cracked,
broken, wOrm-eaten, and hollow. The
outer shell containing the perithecia, which
are small pits or sacs containing the sex
ual spores. These always eight in num-
Der, are borne in asci or cells. These
cells grow slowly during the winter, and
the spores in them ripen from the middle
Of January TO the end of February
Those ripening in February germinate in
from three to five days, if sufficiently
moist. Microscopic investigation proves
that the knots on plums of all sorts, aud
on cultivated, wild, and choke cherries,
are identical: though to the naked eye,
they differ slightly in general appearance,
owing probably to the more favorable cir
cumstances for their growth in some spe-
eies Of the genus prunus than in others.
The remedy against this contagious dis
ease is a very obvious one simply to cut
of and burn the knots and swollen branch
es when and wherever found. This should
be done in autumn as soon as they become
plainly seen by the falling of the leaves.
1t is not sufficient to cut them off for
some of the spores which do not ripen till
late in the winter have been carefully
observed to ripen after the branches were