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76
THE MARINE ALGÆ OF NEW ENGLAND.
of the main branches, is kept distinct by most writers. We have but a very imperfect representation of
the Sphacelarioid group in this country. Stypocaulon and Halopteris are entirely wanting, and of
Sphacelaria we have only S. cirrhosa and S. radicans on the northeastern coast, S. tribuloides in
Florida, and what is supposed to be S. fusca in California. The species of Sphacelaria are variable, and
the determination sometimes uncertain. The apical cells of our Sphacelariæ are frequently attacked by
the unicellular parasite, Chytridium sphacelarum, Kny.
S. CIRRHOSA, (Roth) Ag.; Phyc. Brit., Pl. 178.
Fronds olive-brown, densely tufted half an inch to two inches high; main filaments
erect, several times pinnate with opposite or irregularly spreading branches;
rhizoidal filaments few or wanting; unilocular sporangia .06-7 mm long, globose;
plurilocular sporangia .05 mm broad by .08 mm long, broadly ellipsoidal, secund on
lateral branches, with unicellular pedicels; propagula rather stout, three (2-4) rayed,
usually borne on distinct plants.
Common on Fucus, on which it forms dense globose tufts. Europe.
A variable species, sometimes with regularly opposite branches, at times with irregularly placed long
branches. The propagula vary very much in size, and are generally found on plants which do not bear
sporangia. With us they are much more common than the sporangia. An excellent account of the
propagula is given by Janczewski in the Annales des Sciences, Series 5, Vol. XVII. In the Nereis Am.
Bor. the word propagulum is used by Harvey to signify the contents of the apical cells, and this use of
the word should not be confounded with its present application. The word propagulum as used in the
Nereis is rather equivalent to the term sphacela of other writers. Sporangia are more common in the
winter months, but are found occasionally in summer.
S. RADICANS, (Dillw.) Harv. (S. olivacea, var., Ag.; Pringsheim, l. c.‚ Pls. 9 and 10.—
S. radicans, Phyc. Brit., Pl. 189.)
Fronds olive-brown, half an inch to an inch high, forming dense turfs; filaments
erect or prostrate, branches few, somewhat appressed, rhizoidal filaments often
numerous; unilocular sporangia globose, .04-5 mm in diameter, numerous on the
branches, on very short unicellular pedicels; plurilocular sporangia unknown;
propagula slender, elongated.
On mud-covered rocks between tide-marks.
Newport, R. I.; Wood’s Holl, Mass., and common from Nahant northwards; Europe.
The present species is smaller than the last, and forms small, indefinitely expanded turfs, especially on
the under side of mud-covered rocks, often in company with Ceramium Hooperi. Numerous rhizoidal
filaments are sometimes found at the base, so that different plants are bound together, but the species
is without a false cortex. The name originally proposed for the species by Dillwyn was S. radicans.
Agardh adopts Dillwyn’s later name, S. olivacea, making of the form with numerous rhizoidal filaments
a variety, radicans. Apart from their different habit and place of growth, it is difficult to assign exact
marks by which to distinguish in all cases S. cirrhosa and S. radicans. In the latter the secondary
branches are few and appressed, irregularly placed, never opposite, while in the former they are
numerous, given off at