[Sidenote: Fig. 48. Foliage and fruits of Calamites. 1 and 2. Asterophyllites; 3 and 4. Annularia; 5 and 6. Sphenophyllum.]
The different forms of foliage called Asterophyllites, Sphenophyllum, and Annularia, belong to the one genus Calamites, but they may form, perhaps, well-characterised sections when their fruits are better known. In woodcut 48 representations are given of the foliage and fruit of varieties of Calamites. In 1 and 2 we see the simplest form called Asterophyllites. The leaves are linear and slender, with a single rib. The form called Annularia (3 and 4) differs chiefly in having a larger amount of cellular tissue spread out on either side of the midrib. This form has a different aspect in a fossil state from the other, from its whorls of numerous broad leaves spread out on the surface of deposition, while the acicular leaves of Asterophyllites have penetrated the soft mud, and are generally preserved in the position they originally occupied in reference to the supporting branch. The third form (5 and 6) is called Sphenophyllum, and consists of whorls of wedge-shaped leaves, with one or more bifurcating veins. They occur like those of Annularia, spread out on the surface of the shale.
[Sidenote: Fig. 49. _Araucarioxylon Withami_, Krauss (_Pinites Withami_), from the Coal-measures, Craigleith, near Edinburgh, showing pleurenchyma with disks, and medullary rays. An excellent specimen of a stem of this pine may be seen in the Edinburgh Royal Botanic Garden.
Fig. 50. _Trigonocarpum olivæforme_, an ovate, acuminate, three-ribbed, and striated fruit or seed, which some suppose to be a sporangium of a Lepidodendron, others refer it to Cycadaceæ. Hooker refers it to Coniferæ like Salisburia.]
True Exogenous trees exist in the coal-fields both of England and Scotland, as at Lennel Braes and Allan Bank, in Berwickshire; High-Heworth, Fellon, Gateshead, and Wideopen, near Newcastle-upon-Tyne; and in quarries to the west of Durham; also in Craigleith quarry, near Edinburgh, and in the quarry at Granton, now under water. In the latter localities they lay diagonally athwart the sandstone strata, at an angle of about 30°, with the thicker and heavier part of their trunks below, like snags in the Mississippi. From their direction we infer that they have been drifted by a stream which has flowed from nearly north-east to south-west. At Granton, one of the specimens exhibited roots. In other places the specimens are portions of stems, one of them 6 feet in diameter by 61 feet in length, and another 4 feet in diameter by 70 feet in length. These Exogenous trees are Gymnosperms, having woody tissue like that of Coniferæ. We see under the microscope punctated woody tissue, the rows of disks being usually two, three, or more, and alternating. They seem to be allied in these respects to Araucaria and Eutassa (Fig. 61, p. 74) of the present flora. Araucarioxylon or Pinites Withami (Fig. 49) is one of the species found in Craigleith quarry; the concentric layers of the wood are obsolete; there are 2, 3, or 4 rows of disks on the wood, and 2-4 rows of small cells in the medullary rays. Along with it there have also been found Dadoxylon medullare, with inconspicuous zones, 2, 3, and 4 rows of disks, and 2-5 series of rows of cells in the rays. Pissadendron antiquum (Pitus antiqua) having 4-5 series of cells in the medullary rays, and P. primævum (Pitus primæva), with 10-15 series of cells in the medullary rays, occur at Tweedmill and Lennel Braes in Berwickshire; Peuce Withami (Fig. 1, p. 3) at Hilltop, near Durham, and at Craigleith. Sternbergia is considered by Williamson as a Dadoxylon, with a discoid pith like that seen now-a-days in the Walnut, Jasmine, and Cecropia peltata, as well as in some species of Euphorbia.[14] Sternbergia approximata is named by him Dadoxylon approximatum. Hooker believes from the structure of Trigonocarpum (Fig. 50) that it is a coniferous fruit nearly allied to Salisburia (Trans. Roy. Soc. 1854). Several species of Trigonocarpum occur in the Carboniferous rocks, such as T. olivæforme from Bolton (Plate II. Fig. 5), and T. sulcatum from Wardie, near Edinburgh (Plate II. Fig. 6). Noeggerathia and a few other plants, such as Flabellaria and Artisia, are referred by Brongniart to Cycadaceæ. Flabellaria borassifolia, according to Peach, has leaves like Yucca. Noeggerathia has pinnate leaves, cuneiform leaflets, sometimes fan-shaped; the veins arise from the base of the leaflets, are equal in size, and either remain simple or bifurcate, the nervation (venation) being similar to that of some Zamias.