Fig. 263.—Sphacelaria cirrhosa
Fig. 264.—Sphacelaria plumosa
The genus Sphacelaria contains several British weeds with rigid branched and jointed fronds, most easily distinguished by the tips of the branches, which are flattened, contain a granular mass, and have a withered appearance. S. cirrhosa forms hair-like tufts of slender fibres with closely-set branches on small weeds, the tufts varying from a quarter of an inch to over an inch in length. The fronds are naked at the base, and the spore-cases, which are globular, are arranged on the branches. S. filicina is, as its name implies, of a fern-like appearance, but is very variable in form. Its fronds vary from one to three inches in length, and the spores are arranged singly in the axils of the branchlets. Excluding some rarer species we mention one other example—the broom-like S. scoparia, the frond of which is coarse and very rigid, of a dark-brown colour, two or three inches long, with the lower portion clothed by woolly fibres. Its spores are arranged in clusters in the axils of the branchlets.
Fig. 265.—Sphacelaria radicans
The last genus of the Ectocarpaceæ is Cladostephus, which grows in dark-green tufts, usually five or six inches long, in the deeper tide pools. The fronds are cylindrical, branched, inarticulate, and rigid; and the branchlets, which are short and jointed, are arranged in whorls. The spores are situated in short accessory branchlets, or in masses at the tips of the ordinary branchlets. C. verticillatus is a very common species, the whorled branchlets of which are deciduous in winter, when the accessory branchlets that bear spores begin to develop. C. spongiosus is densely clothed with branchlets, and is of a bushy habit, with a very spongy feeling. It is by some regarded as a variety of C. verticillatus.
The order Chordariaceæ is characterised by a compound gelatinous or cartilaginous frond, consisting of interlacing horizontal and vertical threads. The spores are not external as in the Ectocarpaceæ, but contained in cells in the substance of the frond. In the typical genus the frond has a cylindrical, branched, cartilaginous axis, surrounded by whorls of club-shaped threads and slender gelatinous fibres. We have only one common species—Chordaria flagelliformis, the fronds of which are from four to twenty inches long, of uniform thickness throughout, with long, glistening, soft and slimy branches among which the spores are disposed. It may be found in rock pools at almost all levels.