There is a pretty green hair-like plant which branches and gives off branchlets on one side more than on the other. It comes from a little group of stems on a stone, and forms a small stunted but very elegant bush, three or four inches high. This cladophora lives in the purest and clearest sea-water only, and in rocky pools left by the tide near low-water mark. It is only got at low spring tides at Dingle and Dublin, and it evidently likes the cool sea-water and darkness. A sea-weed called the Adherent Codium forms a velvet-like pile on the surface of rocks in the southwest of England near low-water mark, but it is rare. Sometimes the green velvet-looking film may be three feet across, and it consists of myriads of short cylindrical filaments with simple club-shaped hairs on them. It is soft and gelatinous, sticks to paper, and appears to grow slowly. Another codium, called the amphibious, has been mentioned already. It occupies a different position on the shore to the other. It frequents turf banks on the west of Ireland, in County Galway, where the bog touches the shore. It is a very mesh of entangled filaments, and it dries up to almost nothing in dry weather, and increases and grows again on the coming of the welcome tide, spray, or rain. There is also a large codium with branches, which looks like a sponge. Barnacles and shells, living at low-water mark, in exposed situations on the western shores of Scotland and Ireland, Falmouth, and the Land’s End, have a weed upon them of a purplish-brown color like a “crop of threads” (Nemaleon) of from three to ten inches long. They are slender, solid, and divide in twos from a little expanded base. In some places it chooses particular positions, and in our Irish localities it grows in shallow pools on the granite rocks, and nowhere else. A common weed, sometimes twenty inches in length, varies from pale yellow in shallow water to dark purple in deeper places; it lives at half-tide level, and is made up of tubular fronds filled with watery gelatine. Its tube swells, here and there, and bends at the end in a curious manner. It is called, after a French naturalist, Dumontia. Another weed with a cylindrical stem has many branches, and has swellings at their origin like so many knots. These are air-vessels and help to support the plant, which is rather leathery. It is found on the English and Irish shores, and is called the bladder chain-weed (Cystoseira). But the most elegant of the weeds with air-bladders is called the sea oak (Halidrys) and it is found commonly on rocks and stones in the sea, below half-tide level. The fronds are from one to four feet in length, and the branches bear numerous long pods with compartments in them, the whole looking like a mustard-pod, and these are the air-chambers.