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Desmid
of the month
August 2003
Desmidium
swartzii
Desmidium* is one of the filamentous desmid genera characterized by rather firm
intercellular connections: filaments are only to be disrupted by robust
mechanical pressure. From the Netherlands some four species are known,
of which Desmidium swartzii is the most common. Cells of this species
are triangular in apical view. After cell division daughter cells stick
together so that the filament in question increases in length. Moreover,
cell filaments are markedly twisted, to be seen from a gradual shift in
position of the cellular lobe facing the observer.
In case of conjugation
(almost) all cells in the paired filaments are sexually activated, resulting
into a series of zygospores coupling the empty cell filaments.
* The genus name
of Desmidium - derived from the Greek word 'desmos' (= ribbon,
chain or bond) - presumably gave rise to the family name of Desmidiaceae.
image: ©
Wim van Egmond
Disrupted filament
showing some single cells in apical view (triangular) |
image:
© Wim van Egmond
Two cell filaments
of Desmidium swartzii; notice helical twisting of the filaments
Cell dimensions (l. x br): ca 20 x 50 µm
image: ©
Henk Schulp
Zygospore formation
in Desmidium swartzii |