The true external surface of the cortical investment is marked with longitudinal striæ, without any indications of joints or constrictions; but the position of the original articulations is indicated in some specimens by the _presence of small verticillate scars, to which leaves were appended_[78] as in the example figured by M. Brongniart, of which _Lign. 14, fig. 1_, is a reduced figure. [78] See Mr. Dawes, "On the Structure of Calamites," Proc. Geol. Soc, 1851, vol. vii. p. 197. [Illustration: Lign. 15. Calamites, in Coal Shale. Fig. 1.--Calamites radiatus, with the remains of one of the sheaths.--1/2 _nat._ 2.--Stem, with remains of roots.--1/2 _nat._ 3.--Calamites approximatus, showing the curved lower end of the plant.[79]--1/5 _nat._ ] [79] This specimen has been inadvertently drawn with the base uppermost. The stellate appearance on the upper part of the stem figured in _Lign. 15, fig. 1_, is produced by the zone of leaves which surrounded the joint: this character is entirely distinct from the sheath of the Equisetum shown in _Lign. 12_. This specimen points out the importance of carefully examining and preserving the stone around fossil stems; had this precaution been lost sight of in this instance, no knowledge would have been obtained of this important botanical character. It is rarely that any traces of the roots remain; the fossil figured (_fig. 2_) is from the _Foss. Flor._ A beautiful example of the foliage of a species of Calamites is represented in _Lign. 59, fig. 2_. Upright stems of Calamites occur in the Coal formation near Pictou, in North America; and in one example a group of ten or twelve stems, covering an area of two square feet, sprung from one root.[80] [80] Dawson, Geol. Proc. vol. vii. p. 195. See Sir C. Lyell's Travels in North America, vol. ii. p. 195. * * * * * [Sidenote: FOSSIL FERNS.] Filicites, or Ferns. We now arrive at the consideration of one of the most interesting families of the vascular cryptogamia that adorned the Flora of the ancient world, and the living species of which impart beauty and elegance to the scenery of the countries where they prevail. The most essential character of these vegetables, is that of developing their fructification on the leaves; a fact familiar to every one who has even but cursorily examined the Polypody growing on our walls, or the Brake of our hedge-rows and commons. The largest species of British ferns scarcely exceed four or five feet in height; but the arborescent or tree-ferns, of warm climates, attain an altitude of from thirty to forty feet. There is too this peculiarity in the arborescent forms, that while in our indigenous species the leaves surround the stem, and incline towards the upper part of the plant, the foliage of the former bends downwards, and spreads out from the crown, or summit, into an elegant canopy. [Illustration: Lign. 16. Pecopteris Sillimani; _nat._