Page 27 - Algae

10 Algae: Anatomy, Biochemistry, and Biotechnology

FIGURE 1.12 Uniseriate filament of Stigonema FIGURE 1.13 Multiseriate filament of Stigonema
ocellatum. mamillosum.

(Figure 1.6) the protoplast of some cells of the colony undergoes divisions to form biflagellate
zoospores. These are not liberated but aggregate to form a new colony within the parent
cell wall.

Fragmentation

This is a more or less random process whereby non-coenobic colonies or filaments break into two to
several fragments having the capacity of developing into new individuals.

Resting Stages
Under unfavorable conditions, particularly of desiccation, many algal groups produce thick-walled
resting cells, such as hypnospores, hypnozygotes, statospores, and akinetes.
Hypnospores and hypnozygotes, which have thickened walls, are produced ex novo by proto-
plasts that previously separated from the walls of the parental cells. Hypnospores are present in
Ulotrix spp. (Chlorophyceae) and Chlorococcum spp. (Chlorophyceae), whereas hypnozygotes
are present in Spyrogyra spp. (Chlorophyceae) and Dinophyta. Hypnospores and hypnozygotes
enable these green algae to survive temporary drying out of small water bodies and also allow
aerial transport from one water body to another for instance via birds. It is likely that dinophyceae
cysts have a similar function.