Plants -- Identification; Wild flowers -- Great Britain
The seeds of the Dodder fall from the opened capsules during late summer
and early autumn, alighting on the soil, or on the decomposing foliage
that covers the ground, or on the rough barks of the tree that served as
a host for the parasitic plant. The seeds of many other plants fall
about the same time, but those of the Dodder do not begin to germinate
until about a month later than the majority of these, in the following
season, and consequently the young Dodder plants do not appear before
their future hosts have had time to grow sufficiently large to support
and nourish them. Perennial plants, too, which are attacked by the
Dodder, have also produced strong shoots and leaves from their roots or
underground stems by the time that the parasite begins its search for
ready-made organic food; and it is clear that if the Dodder seeds
germinated earlier in the season, the young plants would starve for want
of suitable herbs to give them support and nourishment.
[Illustration: GREATER DODDER, ON NETTLE--A COMPLETE PLANT.]
When the seed germinates it sends out a filament which penetrates into
the soil and fixes the seedling firmly. The other end grows upward,
carrying up with it a little swollen mass of food-reserve, sufficient to
support the growing seedling until it has had some chance of reaching a
suitable host. The upper end of the seedling now sends out a filament
which rapidly elongates, and, growing upward, searches for some stem on
which to climb.
All this time the little mass of food-reserve is being rapidly
exhausted, and if the young seedling fails to reach a suitable plant on
which to climb it soon dies, for its lower extremity is unable to absorb
sufficient food material from the soil; and the plant itself, having no
chlorophyll, cannot decompose carbonic acid gas and build up organic
material to add to its substance.
[Illustration: THE CLOVER DODDER, WITH A SEPARATE CLUSTER OF FLOWERS
REPRESENTING THE NATURAL SIZE.]
Again, should the young plant fail to reach a favourable support, so
that it is of necessity compelled to trail along the ground, the
filaments which would soon produce suckers when attached to a living
plant have no power to form any structures capable of extracting food
material from a damp soil.
Circumstances being more favourable, however, the upper filament
eventually finds a stem, and immediately begins to twine itself round
it, making a few close coils in a clockwise direction. Should the
support prove to be a dead stem, little wartlike swellings are produced
at points where the two touch, and these serve as a means of attachment
for the climbing filament, but no suckers are formed. If, however, the
filament surrounds a living stem, each of the swellings gives rise to
suckers that penetrate into the tissues of the latter, and withdraw the
organic food necessary for the continued existence of the plant.
Public-domain text, read in full here on John Shaqi.
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