Il
I i
Plectonema. Kirchnexi, Oooke, Qrevillea xi,, p. 75.
A t first attached, bnt soon floating, and forming subglobose
woolly tufts, of a dark bluish green, changing to olivaceous.
Tufts from half an inch to an inch in diameter. Trichomes
radiating, with simple (rarely germinate) branches ; joints one
third or one fourth as long as broad.
S i z e . Filaments '012--015 mm. diam., with sheath.
Plectonema mirabile, Kirch. Alg. Schles. p. 229 (scarcely of
Thuret).
In ornamental water. Pleasure grounds, Kew.
The filaments are much thinner than in P, mirabile and the branches
issue singly from the sheath, and not in pairs, as in that species. From
the dimensions given by Kirchner it seems probable that this is the
species to which he has given the name of P. mirabile.
Plate CJF. iig. 2. a, tuft, natural size, h, trichomes X 400.
FAMILY III. SCYTONEMEÆ.
Filaments with lateral ramifications in which some of the
cells change into heterocysts.
This family is divisible into two sections according to the direction
of the multiplication of the cells.
* Cells only mnltiplying in the direction of the length of the filament.
Scytonema , P etalonema, Symphyosiphon, T o lyp o th x ix ,
Cystocoleus.
** Cells mnltiplying as well in the direction of the breadth of the
filament, at least where the branches, which are always produced by
lateral mnltiplioation, originate.
Stigonema, F ischeza, Haplosiphon.
The last section includes many very doubtful forms, which will probably,
as their development becomes better known, be transferred to
Lichens, of which they are presumably an imperfect condition.
G en u s 107, SCYTONEMA. Ag. (1824.)
Sheath enclosing a single trichome, ramifications produced
by th e deviation of the trichome, which emerges from the side
of the sheath. Ramifications usually geminate, produced by a
fold of the trichome which ruptures outside of the sheatli, and
gives origin to two filaments given off at a rig h t angle.
Heterocysts scattered here and there in the trichome, without
any evident relation to the ramifications.
SCYTONEMEÆ.
S cy tonema myochxous. Ag. Syst. p. 40, No. 13.
265
Stratum tliin, woolly, dark brown (now and then rather
silky) ; trichomes very thick, brown, lucid, slightly curved,
ascending, blue-green within, reddish at the apex ( 5 -6 terminal
joints), distinctly articulate, pseudo-branches for the most part
in pairs, sometimes very long, flaccidly erect, about half the
thickness of the trichomes ; sheath of the trichomes thick, distinctly
lamellose, firm, beautiful yellow-brown, surface quite
smooth, th at of the branches paler, often colourless at the tips,
closed and obtusely rounded, heterocysts oblong or sub-cylindrical,
colourless, about equal to the inner diameter of the
trichomes.
S i z e . Cells '01 mm. diam., witlj sheath -08 mm. diam.
Rabh. Alg. Eur. ii., 254. Hass. Alg. 237, t. 68, f. 2.
Jenn. Tnnb. Wells, 188. Gray. Arr. i., 285. Eng. Bot. ii., t.
2515, t. 2516. Kirch. Alg. Sohl. 225. Harv. Eng. Fl. v.,
365. Harv. Man. 155. Mack. Hib. 236.
Conferva myochrous, Dillw. Conf. t. 19. Eng. Bot. i., t.
1555.
On moist rooks.
Plate CV. fig. 1. a, threads maguified about 60 diam. ; b, portion of
same X 400 ; c, hormogones X 400.
S cy tonema n a ta n s. Breb. in Kutz. Tab. Phyc. II., t. 22, /. 1.
Floccose tomentose, green then brown or olive, trichomes
slender, elongated, becoming brownish, internally æruginous
green, distinctly articulate, joints nearly equal, gi anular, pseudo-
ramuli often in pairs, very slender, more or less distant, very
shortly articulated, sheaths firm, lamellose, yellow or brownish,
rarely uncoloured, branches paler, or colonrless, indistinctly
lamellose, heterooysts interspersed, oblong, or ovoid, pellucid.
S i z e . Threads with sheath -025 mm., without sheath -007
mm.
Eabh. Alg. Eur. ii., 253. Kirch. Alg. Sohl. 224.
In stagnant water.
Plate CF. fig. 2. Portion of trichome with sheath X 400 diam.
S cytonema c in e z eum . Meneg. in Kutz. Spec. 303.
A t first pulvinate, cinereous green, then confluent, forming a
more or less tomentose pulverulent stratnm (becoming pale blue
when dry), now and then violet or purplish ; trichomes very
fragile, elongated, flexuose and curved, loosely interwoveu,
sparingly branching, indistinctly articulate, internally dingy,
2 p