Lign. 41. Stems from the Coal Formation.
| Fig. | 1.— | Halonia regularis. Coalbrook Dale. |
| 2.— | Knorria Taxina. Roof of the High-main Coal seam, Jarrow Colliery. (Brit. Foss. Flor.) |
Halonia.—The specimens usually seen are mere sandstone casts having a thin carbonaceous crust; the stem is branched and beset with large elevated knobs, or subcortical protuberances, as shown in [fig. 1, Lign. 41]. These plants appear to be closely related to the Lepidodendra; their mode of branching is shown in a beautiful specimen (in the museum of the Leeds Philos. Soc.) figured and described by Mr. Denny, which is also remarkable because it indicates the probability that the Haloniæ, and the fossil stems, termed Knorriæ, are identical; for the specimen in question, which in its branches is unquestionably of the former type, has the base of the stem impressed with the leaf-scars of the latter.
Knorria.—To this genus the authors of the Fossil Flora of Great Britain referred those stems which have projecting leaf-scars, arranged spirally. The beautiful specimen figured as Knorria taxina, [Lign. 41, fig. 2], closely resembles a young branch of Yew (Taxus), and perhaps might be more correctly named Taxites.
Bothrodendron and Ulodendron.—These genera, together with Megaphyton, are stems of a very remarkable character, and are easily distinguished by the vertical rows of large and distant scars. The two first have two series of very deep oval depressions on opposite sides of the stems, arranged alternately in the specimens I have examined: from the size and form of these obliquely-oval cavities, it is supposed that they were formed by the attachment of cones, and not by petioles; but their real nature is involved in obscurity.[115]
[115] Figured in Bd. pl. lvi.
In Megaphyton, the large ovate scars indicate the attachment of deciduous branches or gigantic leaves, which did not grow all round the stem, but in a regular order of superposition on each side.[116]
[116] Figured in Pict. Atlas, pl. xxv.