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66
THE MARINE ALGÆ OF NEW ENGLAND.
DICTYOSIPHON, Grev.
(From δικτυον [diktyon], a net, and σιφων [siphon], a tube.)
Fronds olive-brown, filiform, branching, solid above, becoming hollow below, cortex
composed of small, irregularly polygonal cells, interoir of larger, colorless,
longitudinally elongated cells; branches corticated throughout; growth from an
apical cell (scheitel-zelle); unilocular sporangia spherical, scattered, immersed in the
cortex; paraphyses and plurilocular sporangia unknown.
The genus was founded on D. fœniculaceus, a species placed by C. A. Agardh and Lyngbye in
Scytosiphon. Under D. fœniculaceus were included a number of forms which have since been separated
by Areschoug and placed in two different genera, Phlæospora and Dictyosiphon. In the former the
unilocular sporangia are formed directly from the cortical cells and cover the surface in dense patches,
at maturity projecting above the surface of the frond. In the latter genus the sporangia are scattered
and immersed. In Dictyosiphon, moreover, the growth is from an apical cell, but in Phlæospora it is
trichothallic, and in the former genus the superficial cells are polygonal and irregularly placed, while in
the latter they are quadrate and arranged in regular series. The genus is divided by Areschoug into two
subgenera, Dictyosiphon proper and Coilonema, the latter of which is referred by Gobi to Cladosiphon,
since the cortical layer consists of very short filaments rather than a continuous cellular membrane.
Our two species belong to Dictyosiphon proper, but species of Coilonema and Phlæospora are to be
expected in the region of Eastport. By Harvey the genus was placed in the Dictyotacæ, from which order
it was necessarily removed when the true nature of the sporangia was discovered.
D. FŒNICULACEUS, Grev. (Scytosiphon fœniculaceus, Ag.—D. fœnieulaceus, Phyc.
Brit., Pl. 326; Areschoug, Phyc. Mar., Pl. 7.)
Fronds yellowish brown, six inches to two feet long, much branched; branches
alternate or occasionally opposite; superficial cells angularly quadrate.
Common on stones and algæ at low-water mark. Spring and summer. Europe.
A variable species as found on our coast, but one which cannot well be subdivided at present. Early in
the season the fronds are light colored and delicate in substance, but later they become more rigid.
Perhaps some of the forms which we have here included may properly be placed under var. flaccidus of
Areschoug. Such, at least, .appears to be the case with some of the specimens collected in May at
Wood’s Holl.
D. HIPPUROIDES, (Lyngb.) Aresch.? (Scytosiphon hippuroides, Lyngb., Hydr., Pl. 14
b.—D. fœniculaceus α, Aresch., Phyc. Mar., Pl. 6 a and b.—Chordaria flagelliformis
var. β and γ, Agardh, Sp. Alg., Vol. I, pp. 66 and 67.)
Fronds dark brown, four inches to two feet long; main branches rather densely beset
with flagellate, scattered, subequal secondary branches; superficial cells in the lower
part arranged in horizontal series, above irregular.