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490 University of California Publications in Botany [Vol. 8
2. Hecatonema variabile S. and G.
Fronds forming circular cushions, 4-7 mm. diam.; prostrate por-
tion composed of regularly radiating filaments with subterminal
branching, attached by numerous short rhizoids, 1-3 cells long ; erect
filaments not densely crowded, not arising successively from the center
toward the periphery, unbranched, 400-500** long; hairs unknown;
cells of creeping filaments irregular in form, 7-9/* diam.. 1-3 times as
long a.s at the margin; cells of erect filaments 4.5-5/* diam. at the base
and 2-5 times as long, 8-10/* diam. and 1-3 times as long toward the
distal end; zoosporangia (?) broadly clavate, sessile or on short
pedicels on the prostrate filaments, rarely lateral or terminal on the
erect filaments, 50-65/* long, 20-24/* broad; gametangia cylindrical,
tapering slightly at the apices, sessile or on short pedicels on the
prostrate filaments or rarely terminal on the erect filaments, 70-120/*
long, 9-12/* broad ;
loculi 1-2-seriate.
Growing on the pneumatocysts of Nereocystis Luetkeana. Carmel
Bay, Monterey County, California.
Setchell and Gardner, Phyc. Cont. IV, 1922, p. 377. pi. 41. figs.
1-12.
From the standpoint of the structure of the gametangia. the type
of this species of Hecatonema could scarcely be separated from a
Myrionema such as M. phyllophUum S. and G. They, in part, possess
uniseriate loculi, but have many perpendicular and slanting walls,
making a partial biseriate condition. The basal layer, particularly in
the center of the thallus, is distinctly distromatic, developing numerous
pegdike rhizoids, which serve to anchor it more firmly to the host, and.
for the most part at least, the branching of the filaments is subterminal.
whereas that of a true Myrionema is terminal and brought about by
the splitting of the apical cell.
The size of the plants as a whole varies considerably. The material
of the type varies in this respect from 4 mm. to 7 mm. in diameter.
In some collections of specimens which we have included under the
species, the specimens are as small as 2 mm. in diameter, in others
they are up to 10 mm. in diameter. The length of the erect filaments
varies from 150/*, to 500/*. Mature gametangia vary from 55/* to
120/* long. The relative number of gametangia terminal on the
erect filaments, as well as their size and complexity, is exceedingly
variable in different collections. Two or three cells only may meta-
morphose in some filaments, in others eight or ten. Occasionally small