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Vaucheria is a member of the Xanthophyceae (yellow-green algae) and is a very common alga and mostly of freshwater origin, but some are marine, and it can usually be found spread out along the mud like a carpet of green felt. There are about 70 species of this TribophyceaeThis particular species was discovered floating in the still part of a small stream in a huge mass and shaded from the sun by over hanging trees. A small amount was duly collected in a small laboratory container and taken home for further study. Great care must be taken with this alga, especially when trying to tease the filaments out to make a specimen for viewing under the microscope, they tend to tear easily.The name Vaucheria was apparently named after a Swiss clergyman called Vaucher.
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Figure 1.Vaucheria is composed of many tubular filaments which can be very long. The plant is coenocytic and shares it's nuclei and chloroplasts.Note the yellow-green colour of the pigmentation in this photograph. X160 light microscope. There are something in the region of 600 species of Xanthophyta. The Xanthophytes lack any fucoxanthin and do not contain any chlorophyl b. |
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Figure 2. This is an enlargement of a section of a Vaucheria filament showing the hollow tube, which is characteristic of this type of alga.The large central vacuole is seen very clearly in this photograph. |
When viewed under the microscope the long siphonous tubes are immediately recognised, the communal vacuole allows the chloroplasts and nuclei to drift around the plant unhindered.Using the X40 objective the chloroplasts can be seen drifting along the cell walls and aligning themselves to receive the maximum amount of light. The chloroplasts flow along in the cytoplasm.
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Figure 3.This photograph shows the chloroplasts that tend to drift along the inside of the Vaucheria filament. X40 Nomarski objective. |
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Figure 4.Chloroplasts photographed with a X40 phase contrast objective. The drifting of the chloroplasts is quite easy to observe and is most interesting when the light is shone at different angles. |
The chloroplasts do not contain any pyrenoids, the carbohydrates are stored in the form of oil droplets. Growth of the organism takes place at the tip of each filament.Some sections of the filament form specialised regions called holdfasts, and has their name suggests, they prevent the plant from drifting and possibly being washed down stream where damage may occur.
The simplest method in which Vaucheria makes it's self more prolific is to fragment and just let small sections float away and hope that they will reach a suitable environment. This method is preferable when things are going well.
Asexual reproduction can also occur when a zoosporangium forms at the tip of a filament; the oval shaped zoospore will form cilia and is then released into the water. The zoospore will swim away from the main colony where it will locate a suitable environment and begin to construct a cell wall and eventually generate a new thallus. When extreme drought occurs an aplanospore may form. (These are small reproductive cells that are unable to move around but can withstand adverse conditions).
In this respect the Vaucheria alga is quite complex, and unfortunately I have been unable to follow all the stages of the reproductive process. Trying to record all the detail can take up a large amount of time.
This method occurs when the egg and sperm are produced in special sites called the antheridia and oogonium. Both of these reproductive organs can be seen frequently on a mass of Vaucheria. The antheridium are the site of sperm reproduction and consists of a small growth from the main cell which is some what pointed and curved at the tip. The sperms are released from a small opening and will swim away to fertilize an egg which they enter through a small hole in the Oogonial wall.Once this has happened then a zygote with a thick wall will form and sink to the bottom of the stream. Some weeks later a new filament of Vaucheria will start to germinate.
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Figure 5.This photograph shows the two egg cells and the male antheridium. |
This link will take you to the Vaucheria page of Jean Vaucher of the University of Montreal.
http://www.iro.umontreal.ca/~vaucher/Vaucheria.html
Introduction to photomicrography.