Plate LXXV. 



Fig. 351. RIVULARIA PLICATA. 



Colour. Dark green. 



Substance. Smooth; fleshy; shmy. 



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 ^-^ to \ an inch wide. 



Fructification. Minute seeds {zoospores) 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-water mark. Not un- 

 common. 



Duller, darker coloured, and smaller than H. 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 solidi 



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. 



Hahitat. Our coasts generally. On rocks, stones, and algse between tide-marks. 

 Not uncommon. 



Fig. 353. RIVULARIA 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 \ an 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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