Fig. 364.
Asterophyllites foliosa. (Foss. Flo. 25.) Coal-measures, Newcastle.
Asterophyllites.—In this family, M. Brongniart includes several genera, and among them Calamodendron, Asterophyllites, and Annularia. The graceful plant, represented in the annexed figure, is supposed to be the branch of a shrub called Calamodendron, a new genus, divided off by Brongniart from the Calamites of former authors. Its pith and medullary rays seem to show that it was dicotyledonous, and it appears to have been allied, by the nature of its tissue, to the gymnogens, or, still more, to the Sigillaria, which will next be mentioned.
Sigillaria.—A large portion of the trees of the carboniferous period belonged to this genus, of which about thirty-five species are known. The structure, both internal and external, was very peculiar, and, with reference to existing types, very anomalous. They were formerly referred, by M. Ad. Brongniart, to ferns, which they resemble in the scalariform texture of their vessels, and, in some degree, in the form of the cicatrices left by the base of the leafstalks which have fallen off (see [fig. 365.]). But with these points of analogy to cryptogamia, they combine an internal organization much resembling that of cycads, and some of them are ascertained to have had long linear leaves, quite unlike those of ferns. They grew to a great height, from 30 to 60, or even 70 feet, with regular cylindrical stems, and without branches, although some species were dichotomous towards the top. Their fluted trunks, from 1 to 5 feet in diameter, appear to have decayed rapidly in the interior, so as to become hollow, when standing; when, therefore, they were thrown prostrate on the mud, they were squeezed down and flattened. Hence, we find the bark of the two opposite sides (now converted into bright shining coal) to constitute two horizontal layers, one upon the other, half an inch, or an inch, in thickness. These same trunks, when they are placed obliquely or vertically to the planes of stratification, retain their original rounded form, and are uncompressed, the cylinder of bark having been filled with sand, which now affords a cast of the interior.
Fig. 365.
Sigillaria lævigata, Brong.
Stigmaria.—This fossil, the importance of which has already been pointed out, was formerly conjectured to be an aquatic plant. It is now ascertained to be the root of Sigillaria. The connection of the roots with the stem, previously suspected, on botanical grounds, by Brongniart, was first proved, by actual contact, in the Lancashire coal-field, by Mr. Binney. The fact has lately been shown, even more distinctly, by Mr. Richard Brown, in his description of the Stigmariæ occurring in the underclays of the coal-seams of the Island of Cape Breton, in Nova Scotia.