A remarkably graceful class of the coal-plants are known as _asterophyllites_. They had slim fluted and jointed stalks, apparently of humble growth. From each of the joints there sprang two thin opposite branches with stellate clusters of leaflets arranged round them at equal distances. If the reader will take a young rush-stalk, and string along it a number of the flowers of the little star-wort, keeping them a little distance apart, he may form some idea of the appearance of a single branch of the star-bearing _asterophyllite_. Some of the plants embraced under this genus are conjectured to have been aquatic, spreading out their clusters of leaflets in the green sluggish water of stagnant pools; but many of them are evidently related to the calamites, and may possibly have formed part of these plants. Whoever has rambled much in a coal-country, scrambling through briars and brambles in old quarries, or threading his way among the rocks of river-courses, must often have noticed, on the exposed surface of sandstone blocks, dark ribbon-like bands fretted over with little diamond-shaped knobs. They are so common in some districts, that you can scarcely light upon a piece of sandstone which does not show one or more. They belong to a carboniferous plant known as _lepidodendron_ (Fig. 10) or scaly tree, from the peculiar style of ornamentation which adorned its bark. Its structure and affinities have puzzled botanists not a little. A well-preserved specimen reminds one of the appearance presented by a twig of the Scotch fir, when stripped of its green spiky leaflets. The scars thus left at the base of the leaflets are of a wedge-like form, and run spirally up the branch in a manner very like those on the branches of lepidodendron; and it was accordingly supposed at one time that the latter plant belonged, or at least was allied, to the conifers. But the branches of lepidodendron possessed a peculiarity that is shared in by none of our present coniferous trees. They were what botanists call _dichotomous_,--that is, they subdivided into two equal branches, these again into other two, and so on. Their internal texture,[19] too, differed from that of any known conifer. The only tribe of existing plants with which the lepidodendron seems to bear comparison, are the _Lycopodiaceæ_, or club-mosses, of which we have several species in the moor-lands of our own country. They are low trailing plants, with moss-like scaly branches, bearing at their ends shaggy little tufts, whence the popular name of the genus. In warmer climates, they are both more numerous and attain a larger size, sometimes standing erect to about the height of an ordinary gooseberry-bush. But though the lepidodendron appears to have been allied to these plants in structure, it greatly differed from them in dimensions. The club-mosses of the coal-measures shot up as goodly trees, measuring fifty feet and upwards in height, and sometimes nearly five in diameter.