Further Remarks upon the Calamite

Abstract

<h3>Abstract</h3> After noticing the works of some foreign authors who had treated upon the Calamite prior to the date of his last communication*, and with whose researches he was not then acquainted, Mr. Dawes states that, from the observations hitherto made, the Calamite appears to consist of a large central column of tissue, surrounded hy a cylinder of woody structure. This central part, having commonly rotted away soon after the death of the plant, has been replaced by a mineral cast of the inside of the ligneous cylinder, and, owing to the general disappearance of the latter, the jointed and ribbed cast is the usual form in which the Calamite is presented to us in the carboniferous rocks.* The outer ligneous surface appears also to have been ribbed, or rather marked with longitudinal <i>striæ</i>, more or less perfect, but without any indications of joints or constrictions†; the position, however, of these articulations is shown upon some specimens by the presence of small and somewhat oval verticillate leaf-scars, to which may have been appended leaves, corresponding to those attached to Brongniart9s <i>Calamites radiatus</i>‡. These leaf-scars were connected with the small round or ovate processes, usually observed at the joints of the Calamite-cast, by large muriform rays, which passed horizontally through the outer cylinder of woody tissue. These processes have been formerly mistaken for the true leaf-scars of the plant§. This outer woody layer is usually met with only in a carbonized state,—that is, in the shape of a thin coating of crystalline coal‖; but occasionally the structure has been met with well-preserved. It is composed of two distinct tissues, the one cellular, the other pseudovascular. In the transverse section these appear to be arranged in alternating vertical plates, which radiate from the inner aspect of this cylindrical woody layer to its periphery, and correspond with the ribs and furrows seen on the surface of the interior cast. These alternating plates, being of different shades of colour, are sufficiently visible to the unassisted eye¶. The darker stripes, which constitute the pseudo-vascular part of the structure, arise in somewhat wedge-shaped masses from the centre of each furrow, and as this tissue diverges into the cellular part of the stem, a small portion of the parenchyma opposite each adjoining rib is usually left unpenetrated by the vascular fibre*. The lighter-coloured stripes are in fact merely portions of the cellular or parenchymatous structure which have not been so closely interwoven with the pseudo-vascular tissue, emanating from the furrows as before mentioned. The darker-eoloured tissue, when examined in the vertical section, is found to be marked with fine transverse <i>striæ</i>. This differs, however, from true scalariform structure, inasmuch as these peculiar markings, like the <i>areolæ</i> on the walls of the vascular tissues of the <i>Coniferæ</i>, are only to be detected when the sections are cut in the direction of the rays. Indeed these transverse striæ in some specimens are seen to become reticulate, as in the <i>Pinites</i> of the Coal-measures. Moreover, in a transverse section, the wood of the Calamite exhibits a network of quadrangular tissue, similar to what we observe in the <i>Coniferæ</i>.