The genus _Cuscuta_ contains quite a number of species which go under
the common name of dodder, and which have the peculiarily of living as
parasites upon other plants. Their habits are unfortunately too well
known to cultivators, who justly dread their incursions among cultivated
plants like flax, hops, etc.
All parasitic plants, or at least the majority of them, have one
character in common which distinguishes them at first sight. In many
cases green matter is wanting in their tissues or is hidden by a
livid tint that strikes the observer. Such are the Orobanchaccæ, or
"broomropes," and the tropical Balanophoraceæ. Nevertheless, other
parasites, such as the mistletoe, have perfectly green leaves.
However this may be, the naturalist's attention is attracted every time
he finds a plant deprived of chlorophyl, and one in which the leaves
seem to be wanting, as in the dodder that occupies us. In fact, as the
majority of parasites take their nourishment at the expense of the
plants upon which they fasten themselves, they have no need, as a
general thing, of elaborating through their foliar organs the materials
that their hosts derive from the air; in a word, they do not breathe
actively like the latter, since they find the elements of their
nutrition already prepared in the sap of their nurses. The dodders,
then, are essentially parasites, and their apparent simplicity gives
them a very peculiar aspect. Their leaves are wholly wanting, or are
indicated by small, imperceptible scales, and their organs of vegetation
are reduced to a stem and filiform branches that have obtained for them
the names of _Cheveux de Venus_ (Venus' Hair) and _Cheveux du Diable_
(devil's hair) in French, and gold thread in English. Because of their
destructive nature they have likewise been called by the unpoetic name
of hellweed; and, for the reason that they embrace their host plants so
closely, they have been called love weed and love vine.
When a seed of _Cuscuta_, germinates, no cotyledons are to be
distinguished. This peculiarity, however, the plant has in common with
other parasites, and even with some plants, such as orchids, that
vegetate normally. The radicle of the dodder fixes itself in the earth,
and the little stem rises as in other dicotyledons; but soon (for the
plantlet could not live long thus) this stem, which is as slender as a
thread, seeks support upon some neighboring plant, and produces upon
its surfaces of contact one or more little protuberances that shortly
afterward adhere firmly to the support and take on the appearance and
functions of cupping glasses. At this point there forms a prolongation
of the tissue of the dodder--a sort of cone, which penetrates the stalk
of the host plant. After this, through the increase of the stem and
branches of the parasite, the supporting plant becomes interlaced on
every side, and, if it does not die from the embraces of its enemy, its
existence is notably hazarded. It is possible for a _Cuscuta_ plant to
work destruction over a space two meters in diameter in a lucern or
clover field; so, should a hundred seeds germinate in an acre, it may be
easily seen how disastrous the effects of the scourge would prove.
These enemies of our agriculture were scarcely to be regarded as
injurious not very many years ago, for the reason that their sources of
development were wanting. Lucern and clover are comparatively recent
introductions into France, at least as forage plants. Other cultures are
often sorely tried by the dodder, and what is peculiar is that there are
almost always species that are special to such or such a plant, so that
the botanist usually knows beforehand how to determine the parasite
whose presence is made known to him. Thus, the _Cuscuta_ of flax, called
by the French _Bourreau du Lin_ (the flax's executioner), and by the
English, flax dodder, grows only upon this textile plant, the crop of
which it often ruins. On account of this, botanists call this species
Cuscuta epilinum. Others, such as C. Europæa, attack by preference hemp
and nettle. Finally, certain species are unfortunately indifferent and
take possession of any plant that will nourish them. Of this number is
the one that we are about to speak of.
Attempts have sometimes been made out of curiosity to cultivate exotic
species. One of the head gardeners at the Paris Museum received
specimens of _Cuscuta reflexa_ from India about two years ago, and,
having placed it upon a geranium plant, succeeded in cultivating it.
Since then, other plants have been selected, and the parasite has been
found to develop upon all of them. What adds interest to this species
is that its flowers are relatively larger and that they emit a pleasant
odor of hawthorn. Mr. Hamelin thinks that by reason of these advantages,
an ornamental plant might be made of it, or at least a plant that would
be sought by lovers of novelties. Like the majority of dodders, this
species is an annual, so that, as soon as the cycle of vegetation is
accomplished, the plant dies after flowering and fruiting. But here the
seeds do not arrive at maturity, and the plant has to be propagated by
a peculiar method. At the moment when vegetation is active, it is only
necessary to take a bit of the stem, and then, after previously lifting
a piece of the bark of the plant upon which it is to be placed, to apply
this fragment of _Cuscuta_ thereto (as in grafting), place the bark over
it, and bind a ligature round the whole. In a short time the graft will
bud, and in a few months the host plant will be covered with it.
The genus _Cuscuta_ embraces more than eighty species, which are
distributed throughout the entire world, but which are not so abundant
in cold as in warm regions.--_La Nature_.
[Illustration: A NEW EXOTIC DODDER. (_Cuscuta Reflexa_.)]
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