Plate LXXIX. 
Fig. 373. OSCILLATORIA SPIRALIS. 
Colour. The layer greenish-black, or verdigris ; glossy ; dried filaments the same. 
Substance. The layer sometimes leathery, sometimes membranaceous; scarcely gelatinous; 
filaments rigid. 
Character of Frond. A more or less thin layer of short, slender, jointed threads {filaments')^ 
stiJBfly curled and twisted ; turned in all directions ; densely interwoven. Filaments 
apt to break into short fragments ; unbranched ; tubular ; containing narrow, 
cylindrical colour-cells, which show through, with division-lines. 
Measurement. The larger layers sometimes several feet in extent. Filaments about 
an inch long ! 
Fructification. Minute seeds {zoospores) formed of the colour-cells in the filaments ; which 
cells at last separate from each other and fall out. 
Habitat. Our coasts generally. On rocks above and between tide-marks ; often left dry. 
The waving to-and-fro (oscillating) movement of Oscillatoria filaments has been mentioned 
under Tig. 372. 
Fig. 374. SPIRULINA TENUISSIMA. 
Colour. Rich metallic, or verdigris-green. 
Substance. The layer very gelatinous ; slimy. 
Character of Frond. A thin film of excessively slender, wavy, densely-twisted threads {filaments)^ 
lying nearly parallel. Filaments unbranched ; tubular ; containing bright green 
colour-cells, which show through ; their division-lines close, and more or less distinct. 
Measurement. The layer J of an inch or more across. 
Fructification. As above, in Oscillatoria. 
Habitat. On decaying algae, sticks, &c. in brackish pools near Menai Bridge. Pool near 
Dolgelly. Aberdeen. 
The filaments of Spirulina, like those of Oscillatoria and Microcoleus, have, when alive 
and under water, the to-and-fro movement called oscillation, and in Spirulina the movement 
is particularly vivid. 
Fig. 375. OSCILLATORIA MGRO-VIRIDIS. 
Colour. The layer a very dark olive-green, almost black ; dried filaments pale green. 
Substance. The layer soft ; gelatinous ; filaments rigid. 
Character of Frond. A thick layer of very slender threads {filaments), with distinctly curved, 
blunt tips ; at first growing on mud, afterwards floating. Filaments apt to break 
into needle-like fragments ; unbranched ; tubular ; containing pale green colour-cells, 
which show through ; their division-lines inconspicuous ; set at intervals of about 
half the width of the filament. 
Measurement. Indefinite. 
Fructification. As before. 
Habitat. Shirehampton, Bristol. In a brackish ditch. 
157 
