Often at high-water mark, and on wood and stones down to half-tide level, there is a quantity of dark olive-green sea-weed, in small tufts, getting larger nearer the sea, which often looks dried up, shriveled, and crisp. It grows in tufts when the water goes off rapidly, and it evidently requires exposure to the air for several hours in the day. Nearer the ever-rolling sea the plant grows larger. It is called the channeled fucus, and has an expanded part or root, and a stem which branches in twos, and ends in two long cones of softish stuff which contain the reproductive organs or spores, called receptacles. It belongs to the same group of sea-weeds as the commonest of all, or that which has air-bladders on it and which crackle and burst under the feet. A differently colored high-water-mark weed is found at Yarmouth, Bantry Bay, Torquay, and Sunderland on sand-covered rocks. It lies prostrate and is of a pale green color, forming masses or layers of excessively minute threads of vegetable tissue. It belongs to the genus Codium. The sea-weeds called wracks or fucus are among the most common of the dark greenish-olive kinds, and one of them lives in a curious place on the shore. The stem or frond is from one to two feet long; there is a kind of midrib to it, besides the cones or receptacles, at the tip of each branch. It is common from Orkney to Cornwall in many places, and is found where a good deal of fresh water mixes with the sea, but it is not restricted to such peculiar positions, for some of the most vigorous plants live in salt water, and some very transparent and weak ones in brackish water. The common bladder fucus is found everywhere on rocks and stones and wood left exposed at low water, and on artificial quays in estuaries extending up rivers as far as the water is decidedly brackish. Even in salt water it is noticed to flourish. The plant or frond is in long, flat, thin branches with a midrib, on either side of which are the bladders, which contain air. The branches end in thick gummy-feeling masses, which are turgid, rather pointed, and contain the spores. The color is olive and it is lighter in the younger parts. It is found along the shores of the Northern Atlantic, extending even to the tropics. It is used as manure, and also in forming kelp for the purposes of the manufacture of iodine. Cattle eat it in the winter, and of late it has been used in baths. A larger kind of fucus grows from high-tide mark to mid-tide level, and it has large swellings on its stem, and the branches, which come off in whorls, are distended, as it were. It is used in the kelp manufacture and for covering up oysters. The Scotch shore-men call it the sea-whistle, for boys make whistles out of the larger air-vessels. The serrate fucus, so called from its saw-like edges, has no bladders, it clothes the rocks at half-tide level, is very common, and is found on the western shores.