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15 μm
25 μm
50 μm
200 μm
Figure 4.26
Arthrospira
. Top: Detail from spiral fila-
ment showing short disk-shaped cells (arrows). Bottom:
Low power view of filaments showing typical spiral mor-
phology.
Figure 4.25
Nostoc.
Top: Detail from colony, with fil-
aments embedded in a mucilaginous matrix. Bottom:
Low power view of large globular colony. Indian ink
preparation.
The cylindrical trichomes are twisted into
a very regular spiral or helix, with the cell
cross walls difficult to see. Colour variable
from blue-green to violet. Gas vacuoles may
be present. Trichomes (1-8 μm diameter,
depending upon species) can be motile if
in contact with a surface.
Spirulina
(free-
floating or attached) is widespread in both
freshwaters (including saline lakes, mildly
polluted waters) and brackish environments.
Cyanophyta.
heterocysts. Cells are short, with distinct
cross walls. Organisms with these features
were originally placed within
Spirulina
,but
are now given a distinct genus. Cyanophyta.
Fig. 4.26.
(b) Trichomes not forming a regular and
definite spiral. The individual cells of the
trichome usually more easy to distinguish
.....................................
54
Arthrospira
has cylindrical trichomes
(frequently
54
(53) (a) Trichomes without a sheath
............................
Oscillatoria
>
7 μm diameter) and no
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