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 gela- 

 tinous; filaments rigid. 



Character of Frond. A more or less thin layer of short, slender, jointed threads 

 {filaments), stiffly curled and twisted; turned in all directions; densely inter- 

 woven. 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 

 •2V of 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. 

 Sahitat. 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 Fig. 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; contain- 

 ing bright green colour-cells, which show through; their division-lines close, 

 and more or less distinct. 



Measurement. The layer ^ of an inch or more across. 



Fructification. As above, in Oscillatoria. 



Sabitat. On decaying algse, sticks, &c. in brackish pools near Menai Bridge. 

 Pool near Dolgelly. Aberdeen. 



The filaments of Spirulin,a, like those of Oscillatoria and Microcoleus, have, 

 when alive and under water, the to-and-fro movement called oscillation, and in 

 Sjpirulina the movement is particularly vivid. 



Fig. 375. OSCILLATORIA NIGRO-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. ►Shirehanipton, Bristol. In a brackish ditch. 

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