Plate LXXV. 
Fig. 351. RIVULARIA PLICATA. 
Colour. Dark green. 
Substance. Smooth ; fleshy ; slimy. 
Character of Frond. Small, rounded, but irregular lumps ; several growing together in a mass ; 
formed of closely-packed threads {filaments) radiating from a centre. At first solid ; 
afterwards hollow and bursting. 
Internal Filaments. Tubular ; containing very narrow, cylindrical colour-cells, which show 
through, with division-lines ; not branched, but lying against each other as if they 
were ; a globular cell at the bottom of each (a microscopic object). 
Measurement. The patches indefinite ; each frond from tV to J an inch wide. 
Fructification. Minute seeds {zoospo7^es) formed of the colour-cells in the filaments ; which cells 
then separate from each other and drop out. 
Habitat. Our coasts here and there. On rocks near high-w’ater mark. Not uncommon. 
Duller, darker coloured, and smaller than B. nitida. 
Fig. 352. RIVULARIA ATRA. 
Colour. Glossy black. 
Substance. Hard ; fleshy ; smooth. 
Character of Frond. Very minute, bead- or drop-like lumps ; scattered, not massed together ; 
formed of densely-packed threads {filaments) radiating outwards. Always solid. 
Internal Filaments. Tubular ; containing cylindrical colour-cells of various lengths, which show 
through, with division-lines ; not branched, but lying against each other as if they 
were ; a globular cell at the bottom of each (a microscopic object). 
Measurement. Scarcely ever as large as a sweet-pea seed ; generally smaller. 
Fructification. As in the preceding. 
Habitat. Our coasts generally. On rocks, stones, and alg?e between tide-marks. Not 
uncommon. 
Fig. 353. RIVULAKIA NITIDA. 
Colour. A shining deep green ; sometimes verdigris when dry. 
Substance. Leathery, but gelatinous ; slippery feeling. 
Character of Frond. Irregularly round, more or less distorted balls ; several often rising 
together from a lumpy patch ; formed of threads {filaments) radiating from a centre ; 
the inner ones loosely, the outer closely packed. When young, compressed and filled 
with gelatine ; when old, hollow and distended. 
Internal Filaments. Tubular ; containing narrow cylindrical colour-cells, which show through, 
with division-lines ; not branched, but lying against each other as if they were ; a 
globular cell at the bottom of each (a microscopic object). 
Measurement. From | inch to an inch across. 
Fructification. As before. 
Habitat. Southern shores of England. Isle of Man. South and west of Ireland. On rocks 
at half-tide level. Plentiful where it occurs. 
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