Ser. R hodospermeæ. Fam. Gloiocladeæ.
P l a t e C X .
DUDRESNAIA DIVARICATA, J. 4/.
Gen. Char. Frond cylindrical, gelatinous, elastic; axis composed of a lax
net-work of anastomosing filaments, coated with a stratum of closely
combined, longitudinal fibres; the periphery of horizontal, diohotomous,
moniliform filaments. Fnictification, of two kinds on different
individuals; 1, globular masses of spm-es (favellidia) attached to the
filaments of the periphery. 2, external tetraspores, borne on the filaments
of the periphery, generally terminating a ramulus. Dhdres-
NAIA (Bonnem)— m honour of M.
D u d r e s n a ia divaricata-, frond filiform, pale red, very much branched;
branches opposite or alternate, horizontal, once or twice pinnated ;
ramuli numerous, divaricate, irregular, obtuse.
Dudresnaia divaricata, J. Ag. Alg. Medit. p. 85. Endl. 3rd Suppl. p. 37.
Mesogloia divaricata, Ag. Syst. Alg. p. 51. Kiitz. Fliye. Gm. p. 332.
M e s o g l o i a Hudsoni, i ï a i T . Î » Hook. Br. El. vol.ii. p. 386 (not of Ag.).
Harv. in Mack. El. Hih. part 3. p. 186. Wyatt, Alg. Banm. no. 99. H a n .
Man. p. 47.
Ulva rubens, Huds. El. Ang. p. 571.
H a b . On stones, and the smaUer Algæ, near low-water mark, and at a
greater depth. Annual. Summer and autumn. Generally distri
buted round the British shores ; more abundantly in the north. Los
siemouth, Mr. Brodie. Appin, Capt. Carmichael. Arran and Salt
Coats, Bev. B . Landshorough. Orkney, Bev. J. H. FoUexfen, Lieut
Thomas, and Br. Me’Bain. Sidmouth and Torbay, Mrs. Griffiths
Fahnouth, Miss Warren. Jersey, Miss White. Aberfaw, Mr. Balfs
KUliney and KUiee, W. H. H. Howth, Miss Gower. North of
Ireland, Mr. Thompson. Roundstone Bay, Mr. Me’ Calla.
Geogr. D istr. Northern Atlantic, as far south as the French shores of the
British Channel. Baltic Sea.
Descb. Root minute. Fronds densely tufted, 6-8 inches long, or more, about
half a line in diameter, preserving an equal thickness thi’oughout, with a
simple or forked main stem, densely clothed with lateral branches. Lowest
branches longest, the rest gradually shorter towards the apex, so that the
outline is pretty regularly ovate, all very patent, horizontal or divaricate, in
some specimens pretty regularly alternate, in others generaUy opposite,
flexuous, pinnate or hi-pinnate, with divaricating lesser branchlets. Ramuh
numerous, filiform, squarrose. Substance firmly gelatinous and elastic.
Colour a pale red, or red-brown, becoming darker in the herbarium.
Favellæ very commonly produced, imbedded in the whorled filaments of the
periphery, to which they are attached. Tetraspores I have never seen.