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472 University of California Publications in Botany [Vol. 8
Growing- on the base of Viva sp. in the lower littoral belt. Sitka,
Alaska, to central California (Carmel Bay).
Greville, Scot. Crypt. Flora, vol. 5, 1827, pi. 300; Harvey, Phyc.
Brit., vol. 3, 1851, pi. 280; Saunders, Alg. Harriman Exp., 1901,
p. 423, pi. 46, figs. 1, 2; Setchell and Gardner, Alg. N.W. Amer, 1903,
p. 249; Tilden, Amer. Alg. (Exsicc.), no. 350. Not Collins, Holden
and Setchell, Phyc. Bor.-Amer. (Exsicc), no. 1795 (a mixture of
several Myrionemataceae)
.
Myrionema strangulans Greville has been variously interpreted
and the name has frequently been placed as a synonym under M.
vulgare Thnret. In the attempt to determine the exact nature of
M. strangulans, specimens from Greville 's herbarium, from the western
isles of Scotland (but not from Appin, the technical type locality)
have been obtained (through the kindness of Professor Isaac Bayley
Balfour) and carefully studied. From these the description given
above has been drawn up. We find specimens on Viva which agree
with these Greville specimens in every detail, except that the zoo-
sporangia in our plants average slightly larger.
22. Myrionema obscurum S. and G.
Fronds microscopic, distributed more or less irregularly on the
surface of the host ; creeping filaments much branched, very compact
and contorted, forming a pseudoparenchymatous layer ; erect filaments
sparse, unbranched, 40-70/x high ; true hairs unknown ; cells of creep-
ing filaments extremely irregular in shape and size, 4.5-10/x diam. ;
cells of erect filaments cylindrical, 6.5-7.5/a diam., quadrate or nearly
so ; zoosporangia very numerous, sessile on the creeping filaments,
ovoid to broadly clavate, 45-65/x long, 18-30^ broad ; gametangia
unknown.
Growing on the blade of Costaria costata. Moss Beach, San Mateo
County, California.
Setchell and Gardner, Phyc. Cont. II, 1922, p. 346, pi. 32, fig. 6.
Myrionema obscurum seems decidedly distinct from all other
species of the genus. It seems to be a near relative of M. strangulans
Grev. The basal layer is very compact, and adheres very firmly to
the host, following closely the irregularities on its surface. We are
unable to make out whether or not the epiphyte causes the death of the
cells of the host, which seems- to be quite frequent in all of the plants
we have observed. The creeping filaments push among the dead cells
of the host at times. The zoosporangia are numerous and all sessile.