Introduction to the Study of Palæontological Botany

by John Hutton Balfour

Fig. 49. Fig. 50.

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.

The fossils of this period, referred to as Antholithes,[15] have just been shown by Mr. Carruthers to be the inflorescence of Cardiocarpum (Geol. Mag. Feb. 1872), and he proposes to set aside the former name, confining it to the tertiary fossils to which it was originally given by Brongniart, and to use the latter name. The main axis of the inflorescence is simple, stout, and marked externally with interrupted ridges. The axis bears in a distichous manner sub-opposite or alternate bracts of a linear-lanceolate form and with decurrent bases. In the axils of the bracts were developed flower-like leaf-bearing buds, and from them proceeded three or four linear pedicels, which terminated upwards in a somewhat enlarged trumpet-shaped apex. To this enlarged articulating surface was attached the fruit, to which has been given the generic name Cardiocarpum[16] (Fig. 51). The place of attachment is indicated by the short straight line which separates the cordate lobes at the base of the fruit. The fruit is flattish, broadly ovate, with a cordate base and sub-acute apex. It consists of an outer pericarp, inclosing an ovate-acute seed. That the pericarp was of some thickness, and formed probably a sub-indurated rind, is shown by a specimen preserved in the round, and figured (Fig. 53 a). The pericarp is open at the apex; and the elongated tubular apex of the spermoderm passes up to this opening. The seed forms a distinct swelling in the centre of the fruit, and a slight ridge passes up the middle to the base of the apical opening.

Fig. 51. Fig. 52.

Fig. 51. Cardiocarpum Lindleyi, Carr. Fig. 52. Do., Coal-measures, Falkirk.

These fossils are believed to be an extinct form of Gymnosperms. Two species have been described, of both of which we are able to give figures. The first figure is from the specimens collected by Mr. Peach at Falkirk. It is Cardiocarpum Lindleyi (Figs. 51, 52); it has a primary axis with sub-opposite axillary axes, bearing four to six lanceolate leaves and three or four pedicels. Primary bracts short and arcuate. Fruit ovate-cordate, with an acute bifid apex, and a ridge passing up the middle of the fruit.