The Encyclopedia Americana (1920)/Dodder
DODDER, a genus of plants, Cuscuta, of
the family Custcutaceæ. The characteristics of
the group are filiform twining stems, parasitic
on other plants, to which they attach themselves
by suckers. They have lost all trace of leaves,
even the cotyledons of the embryo being no
longer distinguishable, while chlorophyll is
almost completely absent. In one American
species a slight trace of coloring matter has been
noticed. The seed germinates very late in
spring, and as the seedling rises from the
ground a yellow or pink stem soon begins to
show the sweeping movements of circumnutation
of a climbing plant. If no plant known as
the “host” is in the neighborhood for it to take
up its quarters on, it falls to the ground, but
retains its vitality for some weeks, by which time
a victim may probably have germinated. As
soon as it touches a living plant it twines firmly
round it, and a series of small wart-like
adventitious roots (haustoria) are developed, from
the centre of each of which a bundle of
suctorial cells force their way through the
epidermis and cellular envelope into the bast and
press against the woody tissue of the host. The
portion of the dodder stem below this attachment
now dies off and there is then no longer
any connection with the ground. The growing
point again circumnutates until it finds a new
base of attachment upon the same or a different
stem of the host, there to repeat the formation
of suckers. In this way a tangled skein of
threads is formed, over which, late in the season,
the yellow or white flowers develop in
dense clusters and the black seeds are shaken
out of the capsule by the wind or gathered with
the crop. This parasite ins often very injurious,
fields of flax, clover and lucerne sometimes
showing well-marked patches completely
desolated by the pest. These have to be mowed
down and burned before new seed has set;
while pains must be taken to procure seed free
from those of the parasite. Preventive
measures are to make careful examination of the

seed (see ), rejecting any that
contains dodder seed and any produced upon
land known to be infested by dodder. When
observed growing among a crop, frequent hoeing
and burning are often satisfactory.
Pasturing with sheep confined to the infested
patches is also practised, the animals being kept
for several weeks upon the land and given
extra food if necessary. The most satisfactory
treatment, however, is clean cultivation or the
growing of a crop upon which the dodder cannot
grow. There are about 100 species of dodder
of wide geographic distribution, of which
at least 25 are found in the western and southern
parts of North America. The temperate
species are all annual, but some of the tropical
species are perennial. A common American
name is tangle-weed. It is a remarkable
circumstance that Cassytha, a totally unrelated
Oriental genus of Lauraceæ, has not only
assumed the same general mode of life, and the
twining, leafless habit, but germinates and
penetrates in a precisely similar way.