The Scottish specimens conform to these characters in so far as they are known, but not having as yet afforded fruit or internal structure, they cannot be specifically determined with certainty. More complete specimens should be carefully searched for, and will no doubt be found.
In Belgium, M. Crepin has described a new species from the Upper Devonian of Condroz under the name P. Condrusianum (1875). It wants, however, some of the more important characters of the genus, and differs in having a pinnate ramification, giving it the aspect of a fern. In a later paper (1876) the author considers this species distinct from Psilophyton, and proposes for it a new generic name Rhacophyton.
The characters given by Mr. Carruthers, in his paper of 1873, for the species P. Dechenianum, are very few and general: “Lower branches short and frequently branching, giving the plant an oblong circumscription.” Yet even these characters do not apply, so far as known, to Miller’s fucoids or Salter’s rootlets or Goeppert’s Haliserites. They merely express the peculiar mode of branching already referred to in Salter’s Lepidodendron nothum. The identification of the former plants with the Lepidodendron and Lycopodites, indeed, rests only on mere juxtaposition of fragments, and on the slight resemblance of the decorticated ends of the branches of the latter plants to Psilophyton. It is contradicted by the obtuse ends of the branches of the Lepidodendron and Lycopodites, and by the apparently strobilaceous termination of some of them.
Salter’s description of his Lepidodendron nothum is quite definite, and accords with specimens placed in my hands by Mr. Peach: “Stems half an inch broad, tapering little, branches short; set on at an acute angle, blunt at their terminations. Leaves in seven to ten rows, very short, not a line long, and rather spreading than closely imbricate.” These characters, however, in so far as they go, are rather those of the genus Lycopodites than of Lepidodendron, from which this plant differs in wanting any distinct leaf-bases, and in its short, crowded leaves. It is to be observed that they apply also to Salter’s Lycopodites Milleri, and that the difference of the foliage of that species may be a result merely of different state of preservation. For these reasons I am disposed to place these two supposed species together, and to retain for the species the name Lycopodites Milleri. It may be characterised by the description above given, with merely the modification that the leaves are sometimes nearly one-third of an inch long and secund ([Fig. 17], supra, lower figure).
Decorticated branches of the above species may no doubt be mistaken for Psilophyton, but are nevertheless quite distinct from it, and the slender branching dichotomous stems, with terminations which, as Miller graphically states, are “like the tendrils of a pea,” are too characteristic to be easily mistaken, even when neither fruit nor leaves appear. With reference to fructification, the form of L. Milleri renders it certain that it must have borne strobiles at the ends of its branchlets, or some substitute for these, and not naked spore-cases like those of Psilophyton.
The remarkable fragment communicated by Sir Philip Egerton to Mr. Carruthers,[BT] belongs to a third group, and has, I think, been quite misunderstood. I am enabled to make this statement with some confidence, from the fact that the reverse or counterpart of Sir Philip’s specimen was in the collection of Sir Wyville Thomson, and was placed by him in my hands in 1870. It was noticed in my paper on “New Devonian Plants,” in the “Journal of the Geological Society of London,” and referred to my genus Ptilophyton, as stated above under Section II., [page 86] et seq.
[BT] “Journal of Botany,” 1873.
Mr. Salter described, in 1857,[BU] fragments of fossil wood from the Scottish Devonian, having the structure of Dadoxylon, though very imperfectly preserved; and Prof. McNab has proposed[BV] the generic name Palæopitys for another specimen of coniferous wood collected by Hugh Miller, and referred to by him in the “Testimony of the Rocks.” From Prof. McNab’s description, I should infer that this wood may, after all, be generically identical with the woods usually referred to Dadoxylon of Unger (Araucarioxylon of Kraus). The description, however, does not mention the number and disposition of the rows of pores, nor the structure of the medullary rays, and I have not been able to obtain access to the specimens themselves. I have described five species of Dadoxylon from the Middle and Upper Erian of America, all quite distinct from the Lower Carboniferous species. There is also one species of an allied genus, Ormoxylon. All these have been carefully figured, and it is much to be desired that the Scottish specimens should be re-examined and compared with them.
[BU] “Journal of the London Geological Society.”