[99] "On the Coal Strata of Nova Scotia." Amer. Journ. Oct. 1841 and Travels in America, vol. ii. p. 180. [Illustration: Lign. 33. Sigillariæ; _in Coal-shale_. Fig. 1.--A specimen deprived of its carbonaceous bark, except in the interstices of the channels, and showing pits left by the external scars. 2.--The markings of S. Defrancii. (_Vég. Foss. Br._) ] [Sidenote: SIGILLARLÆ.] The stems of Sigillariæ vary in size from a few inches to five feet in diameter; and in length from five to sixty feet; they gradually taper from the base to the summit. A specimen measured by M. Brongniart was forty feet long, one foot in diameter at the base, and but six inches at the top, where it divided into two equal branches. These stems may be readily distinguished from those of other trees with which they are associated, by the fluted surface produced by the deep longitudinal grooves, and the regularly disposed imprints between the channels.[100] The carbonized bark, in large specimens, is often an inch thick, but in small examples is a mere pellicle, and being extremely brittle, flakes off with the slightest touch, leaving the inner surface exposed, with the coal remaining in the deep furrows and pits, as in _Lign. 33, fig. 1_. No traces of leaves, or fruit, in connexion with the stems, have been observed. The subjoined sketches (_Lign._ 33, and 34,) illustrate the usual aspect of these fossils. The difference between the imprints on the outside of the bark, and those on the exposed surface of the stem, from the removal of the cortical covering, is well marked in _Lign. 34_. [100] The stems of some recent dicotyledonous trees from New Zealand, in the possession of Dr. Robert Brown, possess similar longitudinal ribs and furrows, both on the bark and alburnum, or naked wood. [Illustration: Lign. 34. Sigillaria Saullii. _Carb. Manchester._ _a._ The imprints of the petioles on the external surface of the carbonized cortical investment. _b._ The inner surface, exposed by the removal of the crust or bark. ] Internal Structure of Sigillariæ.--Our knowledge of the structure of this numerous tribe of plants, has received an important accession by the discovery of the silicified fragment of a stem, which, fortunately for the advancement of science, was placed at the disposal of M. Adolphe Brongniart. It has been described and illustrated by that eminent botanist, in a memoir which is one of the most valuable contributions to fossil botany that has hitherto appeared.[101]