16. OSCILEATOEIA VIOL ACE A Johnst.
Plate L X X I I . Fig. 10.
Char. “ Mass gelatinous, dark purple. Filaments very
slender, straight, loithout perceptible, transverse striæ, laid
on a thin, compact, greenish substratum.” — Johnston.
O. violacea Johnston, Berw. Fl. p. 264. ; Harv. in Hook.
Br. Flor. p. 377. ; Harv. in Manual, p. 166. Oscillatoria
rubiginosa Carmichael, MS.
Hab. Eapid streams near Berwick upon Tweed: Dr.
Johnston. On stones in the bottoms of rivers, co. Antrim
: D. Moore. Appin : Capt. Carmichael.
When dry, the filaments of this species assume a blackish
green cast, with an evident gloss. The filaments are thicker
than those of O. subfusca, h u t do not, like those of tha t species,
preserve their calibre in drying: they are also more
brittle. Striæ in the dried specimens almost invisible, at a
distance usually of about two diameters from each other.
Dr. Johnston considers this to be the “ Conferva mucosa con-
fragosa rivulis innascens ” of Dillenius.
17. Oscillatoria rupestris Ag.
Plate L X X I I . Fig. 11.
Char. Stratum blackish green, thick, opaque, extremely tough.
Filaments rigid, brittle. Striæ almost imperceptible, at
distances o f about h a lf a diameter.
Ag. Syst. p. 63. ; Harv. Hook. Brit. F l. p. 377. ; Harv. in
Manual, p. 166. O. tenax Carm. MS.
Hab. On the precipitous face of cascades. Appin : Capt.
Carmichael.
“ Stratum extensive, sHmy, remarkably tough and elastic,
black on the surface, ash-coloured underneath: when dry
blackish green. Filaments pale green, straight, or variously
curved, radiating, but not equally in all directions.” — Carm.
3IS . The dried stratum of this species resembles in colour
that of O. muscorum, than which, however, it is much more
tough and elastic : the filaments likewise are much smaller.
They are intermediate in diameter between those of O. subfusca,
and O. violacea, differing also from both in some other
respects.^ They are more brittle than those of O. subfusca,
though like those of tha t species they preserve their diameter
in drying, which is not the case with O. violacea. The striæ
are close, and tolerably evident.
18. Oscillatoria spadicea Carm.
Plate L X X I . Fig. 5. and Plate L X X I I . Fig. 5.
Char. Stratum very thin, spreading. Filaments yellowish
brown, thick, variously curved and twisted. Striæ conspicuous,
and very close.
O. spadicea Harv. Hook. Brit. Fl. p. 378. ; Harv. in
Manual, p. 167.
Hab. On damp mossy earth ; rare. Appin : Capt. Carmichael.
Ireland : Mr. Moore. Cheshunt •. A. H. H.
“ I t occurs in a very thin dark green stratum, spreading to
the extent of several feet, and is hardly to be distinguished
from the mossy earth on which it grows. Filaments short,
straight, curved, or spirally twisted, radiating in all directions,
and possessed of all the movements peculiar to the tribe.” __
Carm.
c. Stratum blackish ; filaments hrittle, not coriaceous.
19. Oscillatoria nigra Vauch.
P late L X X I . Fig. 3.
Char. ^ Stratum black ; when dry bluish black, with long radii.
Filaments pale bluish green, thick. Striæ very distinct
and close.
Hook. Scot. ii. p. 79. Conf. fontinalis Dillw. t. 64.
O. limosa, Grev. Fdin. p. 303. O. nigra Harv. in
Manual, p. 165.