Introduction to Water Plants.
Water Plants Gallery.
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Apart from a few highly specialized species and some general adaptive features, not a great deal more can be said about aquatic plants than can be said about plants in general. In freshwater environments however, plants serve two important functions. They help to oxygenate the water, and they provide refuge and habitat for much of the microfauna which would otherwise be quickly consumed by the smaller fish and other predators. They form a kind of buffer zone which prevents the population of food organisms for the larger pond dwellers from reaching zero -- they are havens of biodiversity.
More notes on aquatic plants will be added at a later date.
Elodea (Canadian Pondweed).
As the name implies, Elodea is something of an exotic import in countries outside North America. It seems to offer little attraction to the rotifers and epiphytic growths which encrust other water plants such as Cladophora, and its leaves and stems are always fairly clean.
Its great attraction for the microscopist is the ease with which it affords a demonstration of cyclosis, or cytoplasmic streaming. The leaves are mostly two cell layers thick, and if a healthy green leaf is removed and mounted on a slide under a coverglass with just sufficient pond water to keep it flat, the movement of the plastids within each cell is easily seen using a forty power objective.
It is believed that similar streaming occurs within most plant cells, but few lend themselves to such convenient examination.
This is a highly recommended exercise, and some pictures of cyclosis in Elodea are shown below.
The high-power darkfield pictures below were taken using a Zeiss-Winkel x90 oil-immersion achromatic objective with inbuilt iris diaphragm, and a Beck focusing darkfield condenser, on Kodachrome 25 transparency film exposed with electronic flash. The generally green colour of the pictures is due to the fact that the illumination is arriving from below, passing through plastids in cells below the plane of focus.
Lemna minor (Duckweed).
The tiny aquatic plant Lemna minor is also called duckweed, and is frequently seen as a uniform carpet across the entire area of even quite large ponds. Many organisms (Hydra, rotifers et al) can be found attatched to the fragile rootlets which hang down from the underside of each leaf.
Click for a picture of a Hydra attatched to a Lemna leaf.
A waxy secretion on the leaf surface produces a high surface tension, ensuring that the leaf always floats on the pond surface.
Nymphaea (Water Lily).
Nymphaea alba is the white water lily, and its leaves float on the water surface attatched to the pond bottom by sloping stems. The pictures below are of thin slices of the stem, unstained, and mounted in water under a coverglass. Sclereids are hardened structures produced by specialized cells, occurring throughout the tissues of the plant.