Page:Quarterly Journal of the Geological Society of London, vol. 27.djvu/274

156 and flattened at the top, exactly as somewhat strong fistulous stems would be. It is obviously impossible that casts of medullary cavities could be preserved in this manner. Neither Sternbergioe nor casts of the pith of Calamodendra ever occur under such circumstances.

3. The stems of Calamites may be seen to have produced leaves and branchlets in such a manner as to prove that they are complete stems preserving their external surface. In my paper on the South Joggins, I figured and described the leaves of C. Cistii as seen attached to the erect stems. I have since, in 'Acadian Geology,' figured those of C. Suchovii, found under similar circumstances; and I have specimens which appear to me to verify the figure given by Lindley and Hutton of the leaves of C. nodosus. I have also obtained beautifully preserved specimens of the leaves of C. transitionis, a species common to the Devonian and Lower Carboniferous. It has been supposed that the scars on the nodes of Calamites are merely the marks of bundles of vessels passing from the interior towards the surface; but it is obvious that, in the case of stems actually producing leaves and branchlets, this cannot be the true explanation, though after seeing the very instructive slices of Prof. Williamson's Calamopitus, kindly shown to me by him, I am prepared to admit that in some specimens, at least, they may represent the "medullary radii," which, as already stated, sometimes appear in addition to the true vascular scars.

4. The leaves of Calamites were not, as is often stated, identical with those of Asterophyllites; and the genus Calamocladus, in which Schimper has placed many plants of the latter genus, is therefore altogether unnecessary. A careful microscopic examination of the leaves which I have found attached to Calamites convinces me that they have distinct characters, and affords an additional link of connexion with Equisetaccae. The leaves of Asterophyllites proper are flat, expanded in the middle, and with a distinct midrib. Those of Calamites are strictly linear, thick, and angled, and are besides marked with transverse lines or striae. Similar transverse lines occur on the branchlets of some modern Equiseta, and are produced by lines of minute stomata. "Well-preserved specimens of Calamite-leaves have precisely the same appearance, so that they may be compared to branchlets of Equiseta deprived of their sheath. Flattened leaves of Calamites, it is true, sometimes present the appearance of a midrib; but this arises either from the prominence of the upper angle, or the appearance of an internal axis through the substance of the leaf. Unless very badly preserved, they can always be distinguished from Asterophyllites or Annularia. The connexion supposed, by Ettingshausen and others, to obtain between Calamites and Asterophyllites has arisen either from accidental association, or from failure to distinguish leaves and stems of Calamites from the corresponding parts of Asterophyllites . The conjecture of Brongniart that some, at least, of the Asterophyllites may be leaves, not of