Another genus—Jania—contains a few coralline weeds that are somewhat like Corallina, but are of a more slender habit and smaller, and have a moss-like appearance. They may be distinguished by the forked branching of the slender frond, and by the position of the conceptacles in the axils of the branches, and not at the tips. J. rubens is a very common red species that grows in tufts on other weeds. It has cylindrical segments, longer towards the tips of the branches; while another and less common one (J. corniculata), found principally on the south coasts, has flattened segments except in the branchlets.
A third genus of the order—Melobesia—contains a very peculiar group of algæ that would certainly never be regarded as plants by those who did not know them. They are apparently mere solid incrustations of calcareous matter, without any jointed structure, and often of very irregular form, covering the surfaces of rocks, shells, or weeds. They are of varying colours, some prevailing tints being dark purple, lilac, rose, and yellow; and they are equally variable in form, some being decidedly lichen-like, some resembling fungoid masses, and others consisting of superimposed leaf-like layers. They are not weeds to be pressed for the collector’s album, but require storing in boxes or trays like sea shells. As in the case of the branched corallines, the hidden vegetable structure may be revealed by dissolving away the carbonate of lime; and the spore-conceptacles, with terminal pores, may be seen scattered irregularly over the surface.
The order Laurenciaceæ contains some beautiful pink, red, and purple weeds with round or flattened branching fronds. They may be known by the disposition of the tetraspores, which are irregularly scattered over the branches; and by the pear-shaped spores in rounded capsules. The typical genus (Laurencia) includes an abundant weed (L. pinnatifida) which was formerly eaten in parts of Scotland, where it is known as the Pepper Dulse on account of its peppery taste. It is found in the tide pools on many parts of the coast, and varies much in size, form, and colour according to the situation in which it grows. The plants which are exposed to the air at low tide are usually small, and of a pale brown colour, while those found in the permanent rock pools at or near low-water mark are larger and dark brown or purple. The fronds are flat and cartilaginous, with stout branches bearing alternate divided branchlets, which are blunt at the tips. The stem itself is unbranched. The spores are pear-shaped, in oval cells; and the tetraspores are irregularly distributed near the tips of the branches.
Another common species, known as the Tufted Laurencia (L. cæspitosa), is very similar to the last mentioned, and is not easily distinguished from it. It is, however, of a bushy habit, while L. pinnatifida is flat, and its fronds are less firm. This species grows on rocks and stones between the tide-marks, and is variegated in colour from a pale green to a purple.
Fig. 254.—Laurencia pinnatifida
Fig. 255.—Laurencia obtusa