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central portion of tlie frond is filled with a watery mucus, through which
run longitudinal jointed fibres, with a narrow, coloured endrochrome and a
wide peUucid limbus, anastomosing together into a lax net-work, with large,
oblong, subhexagonal meshes ; these constitute the axis : the periphery or
outer waU of the frond is formed of very delicate, closely packed, horizontal
tUchotomous, moniHform filaments, which spring from the most exterior of
the fibres of the net-work, and their apices, closely glued together, unite into
the membranous coat of the frond. Pructijicatwn ; 1 , spherical masses of
spores oxfmellidia contained in ovate capsules, furnisbed with a terminal pore,
their waUs formed of moniliform filaments. The mass of spores appears to be
formed by a transformation of the internal net-work. 3. Oblong tetraspores
divided at maturity by three transverse lines, formed from the filaments of
the periphery, and scattered at intervals among them. Cohur a duU purple.
This curious little plant appears to have been first noticed by
Dillenins, in whose Herbarium specimens are preserved, according
to Mr. Turner ; and was next excellently described by
Ligbtfoot, who remarks that its branches resemble “ the jointed
leaves of the Cactus opuntia,” a resemblance which has suggested
the specific name, by which it has since been universally distinguished.
Lightfoot’s trivial name “ repens ” has, however, the
priority ; though no one has adopted it.
Its generic relations were, as appears by the numerous synonymes,
long imperfectly understood, and few Algæ have been more
tossed about from one group to another, until, in 1830, Dr.
Grevüle proposed it as the type of a new genus, in which step
he has since been gladly followed by every succeeding author.
His judgment was formed solely from consideration of the structure
of the frond ; the fructification being unknown to him. The
tetraspores were first described, so far as I am aware, by Prof.
J. Agardh, in his ‘ Algæ Mediterraneæ,’ his specimens having
been received from Professor Meneghini, and they have been
excellently figured hy Kiitzing, in his great work. In this
country both kinds of fruit were discovered by Mrs. Griffiths, to
whose kindness I am indebted for all the specimens I have seen.
C. opuntia can only be confounded with a dwarf state of
Chylocladia articulata, which is about the same size. But, not
to speak of difference of structure, the brighter colour, cylindrical
joints, delicate substance, acute angles, and forked fronds of the
latter, sufficiently distinguish it.
Fig. 1. Ca t e n e l l a OPUNTIA :—o /a e » ii/» ra /8Îre. 3. Fronds, 3. A joint bearing
a ceramidium. 4. Ceramidium cut open. 5. Spores, from the same. 6.
Longitudinal section of the frond. 7. Transverse semi-section, with tetraspores
in situ. 8. A tetraspore :■—all more or less Uglily magnified.
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