ZYGNEMA.

A common fresh water alga.

by Steve Durr, UK

Zygnema belongs to the Chlorophyceae and is a conjugate alga.

Zygnema is a very common alga and is usually found along side Spirogyra in quite still waters. Zygnema can be instantly recognised by the two stellate chloroplasts that are embedded in each filament. The very dark regions in the above photograph are probably where the pyrenoids are located. There are many species of Zygnema and it is very difficult to establish which species that you have, G.W.Prescott in his book (How to know the freshwater algae) states that species can be identified by the zygospores that they produce, being round, oval etc. When viewed in the water the filaments look a yellow - green colour, and like Spirogyra are slimy to the touch. I have been unable to observe the reproduction of this alga because it does not appear to occur quite has frequently as in Spirogyra. I am hoping to get further samples so I can make more observations this spring.

Reproduction can occur in three ways: - Asexual, sexual and vegetative.

• Asexual reproduction is by the formation of what are called akinetes and usually only occurs when conditions have deteriorated. An akinete is like a spore and has a very thick wall for protection. The sexual material of any two cells does not come into contact.
• Sexual reproduction happens when the going starts to get tough. Two filaments lie side by side and a conjugation tube will start to grow from one filament towards the other. The genetic material from both plants start to move towards the centre of the tube where they fuse together and form a zygospore. This zygospore will then sink to the bottom of the pond and await favourable conditions. Two types of conjugation occur scalariform and lateral.
• Vegetative reproduction is where the filaments fragment and divide into new cells and this usually happens when there is an abundance of chemicals that the plant can use.

The large bridge that traverses from one chloroplast to the other is where the nucleus resides.

The above photograph was taken with T-Max 100, using a X50 water immersion lens.

Any comments to steve@durr.demon.co.uk.

If you have time, please visit my Web Site.

Editor's note: Steve's web site has some fine photomicrographs and practical advice on many aspects of photomicrography.

Microscopy UK Front Page
Micscape Magazine
Article Library

© Microscopy UK or their contributors.

Published in the June 1999 edition of Micscape Magazine.

Please report any Web problems or offer general comments to the Micscape Editor,
via the contact on current Micscape Index.

Micscape is the on-line monthly magazine of the Microscopy UK web
site at Microscopy-UK