^C. filum.^ Entire frond cylindrical, divided internally by transverse septa; one fourth to one half of an inch in diameter, tapering at each end; ordinarily one to twelve feet long, but sometimes attaining a length of forty feet. When young the frond is covered with fine, transparent hairs; later it is brown and leather-like. The growth takes place at the base, just above the disk-like holdfast, and at the apex it is constantly dying off. The species is common on Northern shores, at and below low-water mark. Often it is in masses which seem like meadows of waving grass under water. Various small algæ and many zoöphytes are to be found on the fronds. (Plate XII.)
This genus is readily distinguishable by the fact that it has leaflets below the lamina. It is found north of Cape Cod.
^A. esculenta.^ Stem compressed, four to twelve inches long, one fourth to one half of an inch wide, and running like a midrib through the lamina; lamina one to ten feet long, two to ten inches wide, frequently torn and ragged; margin wavy; leaflets three to eight inches long and without midrib, growing on both sides of the stem, below the lamina. The spores are produced in the leaflets in the autumn. This is an edible alga and is used as food in Scotland and Ireland, where it is called henware, badderlocks, murlins, and so on. (Plate XII.)
^A. Turneri.^ Stem two to twelve inches long, round below, flattened above, and extending like a midrib through the lamina; lamina one foot to four feet long, with holes over the whole surface; margin wavy. The perforations in the lamina are produced by conical hollow papillæ which cover the young frond and which at length burst, leaving a hole which enlarges as the plant expands. This species is found from Cape Cod to Greenland.
There are other species, which differ from this one in the size of the perforations, the shape of the lamina, and the prominence of the midrib. Harvey describes the plant as an arctic genus growing ten to twelve feet long. (Plate XII.) [pg070]
The plants of this genus are all large, varying from one foot to twelve feet or more in length. They are of wide geographical range, and are more numerous in species than any others of the order. They are commonly known as oarweeds, tangle, devil's-aprons, sole-leather, kelp, sea-furbelows, and so on.