The process of asexual reproduction
In desmids, asexual reproduction
takes place by simple cell division. In the first instance it is the nucleus,
situated in the centre of the isthmus, that multiplies (a process which is hardly
or not to be observed light microscopically as it requires fixation and staining
with specific dyes).
Following this process, between
the daughter nuclei a new cell wall, as a transverse septum in the lengthened
isthmus, is constituted. Subsequently, the istmial compartments separated by
this septum gradually grow to new semicells. The mutual contact between the
two developing, young semicells is maintained for a long time so that cell division
results in formation of a couple of daughter cells which initially, by way of
their young semicells, are still linked to each other.
Sometimes, the above-described succession of cell division stages is interrupted or disturbed. If, after nuclear division in a mother cell, no transverse septum between the two daughter nuclei is constituted the bulging new semicells mutually will not get separated so that a kind of Siamese twin is created. Presumably, such cell anomalies are doomed to die off.