Filaments result from cell division in the plane perpendicular to the axis of the filament and have
cell chains consisting of daughter cells connected to each other by their end wall. Filaments can be
simple as in Oscillatoria (Cyanophyta) (Figure 1.7), Spirogyra (Chlorophyta) (Figure 1.8), or Ulothrix (Chlorophyta) (Figure 1.9), have false branching as in Tolypothrix (Cyanophyta)
(Figure 1.10) or true branching as in Cladophora (Chlorophyta) (Figure 1.11). Filaments of Stigonema ocellatum (Cyanophyta) (Figure 1.12) consists of a single layer of cells and are
called uniseriate, and those of Stigonema mamillosum (Cyanophyta) (Figure 1.13) made up of
multiple layers are called multiseriate.
FIGURE 1.7 Simple filament of Oscillatoria sp.
FIGURE 1.8 Simple filament
of Spirogyra sp.
FIGURE 1.9 Simple filament
of Ulothrix variabilis.
FIGURE 1.10 False branched filament of Tolypothrix byssoidea.
FIGURE 1.11 True branched filament of Cladophora glomerata.
FIGURE 1.12 Uniseriate filament of ocellatum
FIGURE 1.13 Multiseriate filament of Stigonema mamillosum.
FIGURE 1.14 Siphonous thallus of Vaucheria
FIGURE 1.15 Pseudoparenchymatous thallus of Palmaria palmata.
These algae are characterized by a siphonous or coenocytic construction, consisting of tubular
filaments lacking transverse cell walls. These algae undergo repeated nuclear division without
forming cell walls; hence they are unicellular, but multinucleate (or coenocytic). The sparsely branched tube of Vaucheria (Heterokontophyta) (Figure 1.14) is an example of coenocyte or
apocyte, a single cell containing many nuclei.