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HYDROCHARIDEAE , in botany, a naturalSee also: order of Mono-
cotyledons, belonging to the series Helobieae
.
They are See also: water-
See also: plants, represented in Britain by See also: frog-bit (Hydrocharis Morsus-
ranae) and water-soldier (Stratiotes alaides)
.
The order contains
about fifty See also: species in fifteen genera, twelve of which occur in
fresh water while three are marine: and includes both floating
and submerged forms
.
Hydrocharis floats on
the See also: surface of still
water, andhas rosettes
of See also: kidney-shaped
leaves, from among
which spring the
flower-stalks; stolons
bearing new leaf-
rosettes are sent out
on all sides, the plant
thus propagating itself
in the same way as
the See also: strawberry
.
Straliotes abides has a
rosette of stiff sword-
like leaves, which when
the plant is in flower
project above the
surface; it is , also
stoloniferous, the
See also: young rosettes sinking
to. the bottom at the
beginning of winter
and rising again to the
surface in the spring
.
Vallisneria (See also: eel-grass)
contains two species,
one native of tropical
,See also: Asia, the other . in-
habiting the warmer
parts of both hemi-
See also: spheres and reaching
as far See also: north as See also: south
Frog-bit—male plant. the mud at the bottom
I, See also: Female flower. of fresh water, and the
2, Stamens, enlarged. See also: short See also: stem bears a
3, Barren See also: pistil of male flower, enlarged. cluster of long,
4, Pistil of female flower. g, narrow
5, Fruit. grass-like. leaves; new
6, Fruit cut transversely. plants are formed at
7, mod' the end of See also: horizontal
8, 9, Floral diagrams of male and female
See also: flowers respectively. runners
.
Another type
s, Rudimentary stamens. is represented by
Elodea canadensis or
water-See also: thyme,which has been introduced into the See also: British Isles from North See also: America
.
It is a small, submerged plant with long, slender branching stems bearing whorls of narrow toothed leaves; the flowers appear at the surface when mature
.
Halophila, Enhalus and Thalassic are submerged maritime plants found on tropical coasts, mainly in the See also: Indian and Pacific oceans; Halophila has an elongated stem rooting,at the nodes; Enhalus a short, thick rhizome, clothed with black threads resembling See also: horse-hair, the
persistent hard-bast strands of the leaves; Thalassic has a creeping rooting stem with upright branches bearing crowded strap-shaped leaves in two rows
.
The flowers spring from, or are enclosed in, a spathe, and are unisexual and See also: regular, with generally a calyx and corolla, each of three members; the stamens are in whorls of three, the inner whorls are often barren; the two to fifteen carpels See also: form an inferior ovary containing generally numerous ovules on often large, produced, parietal placentas
.
The fruit is leathery or fleshy, opening irregularly
.
The seeds contain a large embryo and no endosperm
.
In Hydrocharis (fig . I), which is dioecious, the flowers are See also: borne above the surface of the water, have conspicuous See also: white petals, contain honey and are pollinated by in-sects
.
Stralioles has similar flowers which come above the surface only
for
See also: pollination, becoming sub-merged again during ripening of the fruit
.
In Vallisneria (fig
.
2), which is also dioecious, the small male flowers are borne in large numbers in short-stalked spathes; the petals are minute and See also: scale-like, and only two of the three
stamens are !fer- FIG. z.—Vallisneria spiralis—Eel grass--tile; the flowers about i natural See also: size
.
A, Female plant; B, become detached Male plant
.
before opening and rise to the surface, where the sepals expand and form a float bearing the two projecting semi-erect stamens
.
The female flowers are solitary and are raised to the surface on. a long, See also: spiral stall:; the ovary bears three broad styles, on, which some of the
large, sticl.•y pollen-grains from the Iloatmg male floc: ers get de-posited (fig
.
3)
.
After pollination the female flower becomes See also: drawn below the surface by the spiral See also: con-See also: traction of the long stalk, and the fruit ripens near the bottom
.
Elodea has poly- FIG
.
3
.
gamo.us flowers (that is, male, female and hermaphrodite), solitary, in slender, tubular spathes; the male flowers become detached and rise to the surface; the See also: females are raised to the surface when mature, and receive the floating pollen from the male
.
The flowers of Halophila are submerged and apetalous
.
The order is a widely distributed one; the marine forms are tropical or subtropical, but the fresh-water genera occur also in the temperate zones
.
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