J
1. P e t a l o n em a a l a t u m .
Plate L X V I I I . Fig. 6.
Char. Filaments hroadiy membranaceous.
P. alatum Berk., Glean, of jVlg., p. 23. t. 7. fig. 2. Oscillatoria
alata Carm. Grev. Crypt. Fl. 222. ; Harv. in
Hook. Br. Fl. 378. ; Harv. in Manual, p. 168.
Hab. On wet calcareous cliffs, Appin : Cajd. Carmichael.
Oban : Rev. 31. J. Berkeley. Aberdeen : Dr. Dickie.
This highly curious plant forms a brownish or chestnut-
coloured stratum, suhgelatinous. The filaments, which are
irregularly branched, central, consist of a coloured thread,
Avhlch is distinctly annulated, and a broad colourless striated
sheath, obtuse at its extremity. The contrast between the
coloured and uncolourcd portions of the filaments, and the
delicate striæ on the sheath, render this a very beautiful
object.
26. A E T H R O N FM A Hass.
Char. Filaments simple, rarely branched? o f equal diameter,
divided into successive portions.
Derivation. From apdpov, a joint, and vyga, a thread.
I t is not without some hesitation that I have ventured to
constitute a new genus for the reception of this curious production,
which could not consistently I think be allowed to
remain Avith either Scytonema or Hassallia.
1. A rthronema cirrhosum Hass.
Plate L X V I I I . Fig. 7.
Char. Filaments o f considerable size, striæ. close and evident.
Scytonema cirrhosum Carm. T u fts widely spread!n g ,/Z a-
ments floating in bundles, spuriously ? branched ;
branches beset with fragments toAvards the top.” —
Carm. 3 iS .
Harv. in Hook. Br. Flor. p. 366.; Harv. in Manual, p. 155.
Hab. Borders of lakes at Lismore Island : Captain Carmichael.
“ I t occurs in continuous fleeces parallel to the Avater’s
edge, of a deep chestnut colour Avhen lying flat, dark olive
Avhcn floating. The fleeces are made up of small, contiguous
fasciculi of interlaced filaments. The filaments arc from
half an inch to an inch in length, simple or spuriously (?)
branched, and prolonged hy successive adhesions of portions,
seemingly of broken filaments, which at length coalesce and
form a knot at the points of adhesion. The transverse striæ
are close and conspicuous.”— Carm.
Fach filament, at regular distances, is obliquely divided :
these divisions are not formed by “ successive adhesion of
portions,” but by the partial separation into portions of a
single filament, the investing membrane or sheath remaining
entire. “
Section ii. G a l o t h r i c ë æ .
“ I have seen upon a Calothrix, gathered in the ponds of
Avater proceeding from the overflowing of the Seine, secondary
oblong branches formed, which at first sight presented
no difference of organization with tha t of the principal
tube. These branches presented transverse approximate internal
divisions, and were filled with endochrome of a very
pale green tint. Shortly after their appearance, I have seen
the^ contents of these branches pierce the external envelope,
Avhich it left empty and transparent, and issue under the
form of a tubular body, oblong, partitioned, obtuse at both
extremities like the principal filament. Unfortunately I
have not been able to folloAv their developement, because the
filaments themselves have become destroyed, or covered witli
crystals resembling those of Chætophora.” — P . 333,
Mr. Dilhvyn, in his “ Introduction to the British Con-
fervæ,” makes some remarks of the same nature in reference
to C. distorta.