SIGILLA'BIA, a genus of fossil plants which are of importance because of their sings lar structure, and their remarkable abundance in the coal measures. They seem to hay. contributed more than any other genus of plants to the formation of coal. The roots of sigillaria are found preserved in the shale which forms the floor of all coal-seams. These roots were originally supposed to be distinct plants, and have received tthe generic name of stigmaria. The most feasible notion, and that generally accepted regarding then), was that they were fleshy water-plants, with numerous linear leaves, articulated to the stem by papilla;, which were buried in deep Eylindrical hollows in the stem. Brongniart first suspected that they were roots, and Binney placed the question beyond doubt by discovering a specimen in which the trunk of a sigillaria rose from the crown of a stig maria. Several observers have subsequently seen these fossils also in actual contact. It is believed that the mud (now converted into shale) in which they grew was very soft, and easily permitted the passage of the large' roots, while they gave off all around innumerable large hollow rootlets. The stems of sigillaria are abundant in the coal-beds: They are marked by parallel longitudinal flutings, and regular scars formed by the base of the leaf-stalks, which had fallen off. They are known to have attained a height of 70 ft. and a diameter of 5 feet. The stem rose without branching till near the summit, wheu it branched several times dichotomously. The proportion of woody matter to cel lular tissue in the stem was very small. The woody fiber is characterized by the
abundance of scalariform vessels, similar to those which occur in lepidodendron, and in the recent vascular cryptogamia. The stem is seldom found preserved so as to exhibit any structure, or even its cylindrical form; it generally occurs as a double layer of coal, showilng on the outer surfaces the scars produced by the bases of the leaf-stalks. The form and arrangement of these scars have been used to distinguish the species, and, indeed, no other materials exist, for hitherto no foliage of any kind has been certainly found connected with the trunks. The restoration of the genus has been consequently quite imaginary. Some, with Brongniart, have supposed that the trunk terminated in a crown of simple leaveS, like that of many palms, and that it was a gymnosperm near to the cycads. Others, with King, consider that the fronds of pecopteris nervosa, which are very abundant in the coal measures, are its foliage, and they would restore it so as to have the appearance of a modern tree fern. And others, with Binney, consider that its affinities are nearer to lepidodendron, and that some of the numerous fragments which have been referred to this genus may really be the branches of the sigillaria. They would restore it as if it were a huge lycopodium, and refer to it some of those fruits which, under the names of lepidostrobus and fiemingites, have been described by Brown, Hooker, and Carruthers.