R I V U L A R I A atra.
Small B la ck Rivularia.
CRYPTOGAMIA Algæ.
Gen. Char. Frond gelatinous, firm, destitute of an
external cuticle. Fructification among jointed filaments,
lodged in the substance of the frond.
Spec. Char. Hemisphærical, solitary, sessile, hard,
black. Internal filaments straight, compact, branched,
concentric, green ; their joints cylindrical.
Syn. Rivularia atra. Roth Catalect. v. 3. 340.
COMMUNICATED by Mr. W. Borrer, in Oct. 1806, from
the piles of Yarmouth jetty , or ju tty , which are constantly
washed by the sea. Mr. W . J . Hooker has observed the same
species on mud in the salt-marshes at Cley.
Dr. Roth justly compares its size to the seeds of mustard or
hemp. It grows more or less scattered, each plant being solitary
and unconnected, sessile, hard, of so very dark a green
as to look black, having a slimy gloss from the pellucid, colourless,
soft, gelatinous superficial filaments. A perpendicular
section shows the internal filaments to be of a dull green, radiating
from the centre, closely compacted and parallel, but
branched. Their joints appear to us numerous, short, cylindrical
: Roth describes them as few and very long.