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REPORT OF THE COMMISSIONER OF FISH AND FISHERIES. 65
internal portion consisting of an axial filament formed of a single row of rather large
cylindrical cells, surrounded by a mass of oblong cells Sometimes mixed with smaller
winding cells; in the spring fronds covered with branching hairs, which drop off later
in the season; unilocular sporangia formed directly from the cortical cells, which do
not undergo any change in shape or size; growth trichothallic.
A small genus, consisting of about fifteen described species, a considerable portion of which bear a close
resemblance to D. aculeata. They are inhabitants of the colder seas in both the northern and southern
hemispheres. Our two species are very widely diffused, but D. ligulata, a common species of California
as well as of Europe, is wanting on our coast. The genus is easily distinguished from its allies by the
axial filament and the formation of the zoospores in the unchanged superficial cells.
D. ACULEATA, Lamx., Phyc. Brit., Pl. 49; Ner. Am. Bor., Vol. I, Pl. 4 b.
Fronds dark olive-brown, one to six feet long, terete below, compressed above, naked
at the base; branches alternate, numerous, long and virgate, lower branches longer
than upper, several times pinnate, clothed in spring with hairs, which fall off and
leave alternate, distichous, spine-like processes.
Common on exposed shores below low-water mark. Throughout the year. Europe.
A coarse and homely species as usually found; often washed ashore in large masses. Not likely to be
confounded with any other of our species. In spring it presents a feathery appearance, owing to the
tufts of hairs with which the frond is beset. It is one of the species used as a fertilizer on the northern
coast of New England.
D. VIRIDIS, Lam. (Dichloria viridis, Grev.—Desmarestia viridis, Phyc. Brit., Pl. 312.)
Fronds light olive, one to three feet long, cylindrical or but slightly compressed;
branches all opposite, distichous, several times pinnate, ultimate branches capillary.
Common on stones at and below low-water mark. Europe.
A smaller and much more delicate species than the last, for which it can never be mistaken, rather
resembling in some of its conditions a Dictyosiphon. The name is derived from the fact that on decaying
or on being placed in fresh water it turns quickly to verdigris-green. Harvey mentions that air-cavities
are to be seen in cross-sections of the filaments. The air-cavities are, however, merely the sections of
the larger cells which are surrounded by dense masses of smaller cells, whereas in D. aculeata a crosssection
shows the axial filament surrounded by a mass of cells of nearly equal diameter.
FAMILY DICTYOSIPHONEÆ.
Fronds branching, filiform, axis composed of elongated cuboidal cells, the cortex of
smaller roundish cells; unilocular sporangia spherical, scattered or aggregated,
formed from the subcortical cells; plurilocular sporangia unknown.
S. Miss. 59——5