The Geological History of Plants

by Sir John William Dawson

The only species known to me in the Devonian of Europe is the Caulopteris Peachii of Salter, figured in the “Quarterly Journal of the Geological Society” for 1858. The original specimen of this I had an opportunity of seeing in London, through the kindness of Mr. Etheridge, and have no doubt that it is the stem of a small arborescent fern, allied to the genus Caulopteris, of the coal formation.

In my paper on the Devonian of Eastern America (“Quarterly Journal of the Geological Society,” 1862), I mentioned a plant found by Mr. Richardson at Perry, as possibly a species of Megaphyton, using that term to denote those stems of tree-ferns which have the leaf-scars in two vertical series; but the specimen was obscure, and I have not yet obtained any other.

More recently, in 1869, Prof. Hall placed in my hands an interesting collection from Gilboa, New York, and Madison County, New York, including two trunks surrounded by aërial roots, which I have described as Psaronius textilis and P. Erianus, in my “Revision of the Devonian Flora,” read before the Royal Society.[BF] In the same collection were two very large petioles, Rhachiopteris gigantea and R. palmata, which I have suggested may have belonged to tree-ferns.

[BF] Abstract in “Proceedings of the Royal Society,” May, 1870; also “Report on Erian Plants of Canada,” 1871.

My determination of the species of Psaronius, above mentioned, has recently been completely confirmed by the discovery on the part of Mr. Lockwood, of Gilboa, of the upper part of one of these stems, with its leaf-scars preserved and petioles attached, and also by some remarkable specimens obtained by Prof. Newberry, of New York, from the Corniferous limestone of Ohio, which indicate the existence there of three species of tree-ferns, one of them with aërial roots similar to those of the Gilboa specimens. The whole of these specimens Dr. Newberry has kindly allowed me to examine, and has permitted me to describe the Gilboa specimen, as connected with those which I formerly studied in Prof. Hall’s collections. The specimens from Ohio he has himself named, but allows me to notice them here by way of comparison with the others. I shall add some notes on specimens found with the Gilboa ferns.

It may be further observed that the Gilboa specimens are from a bed containing erect stumps of tree-ferns, in the Chemung group of the Upper Devonian, while those from Ohio are from a marine limestone, belonging to the lower part of the Middle Devonian.

1. Caulopteris Lockwoodi, Dawson.—Trunk from two to three inches in diameter, rugose longitudinally. Leaf-scars broad, rounded above, and radiatingly rugose, with an irregular scar below, arranged spirally in about five ranks; vascular bundles not distinctly preserved. Petioles slender, much expanded at the base, dividing at first in a pinnate manner, and afterwards dichotomously. Ultimate pinnæ with remains of numerous, apparently narrow pinnules.

This stem is probably the upper part of one or other of the species of Psaronius found in the same bed (P. Erianus, Dawson, and P. textilis, Dawson).[BG] It appears to have been an erect stem embedded in situ in sandstone, and preserved as a cast. The stem is small, being only two inches, or a little more, in diameter. It is coarsely wrinkled longitudinally, and covered with large leaf-scars, each an inch in diameter, of a horseshoe-shape. The petioles, five of which remain, separate from these scars with a distinct articulation, except at one point near the base, where probably a bundle or bundles of vessels passed into the petiole. They retain their form at the attachment to the stem, but a little distance from it they are flattened. They are inflated at the base, and somewhat rapidly diminish in size. The leaf-scars vary in form, and are not very distinct, but they appear to present a semicircular row of pits above, largest in the middle. From these there proceed downward a series of irregular furrows, converging to a second and more obscure semicircle of pits, within or below which is the irregular scar or break above referred to. The attitude and form of the petioles will be seen from [Fig. 24], supra.

[BG] Memoir on Devonian Flora, “Proceedings of the Royal Society,” May, 1870.

The petioles are broken off within a few inches of the stem; but other fragments found in the same beds appear to show their continuation, and some remains of their foliage. One specimen shows a series of processes at the sides, which seem to be the remains of small pinnæ, or possibly of spines on the margin of the petiole. Other fragments show the division of the frond, at first in a pinnate manner, and subsequently by bifurcation; and some fragments show remains of pinnules, possibly of fertile pinnules. These are very indistinct, but would seem to show that the plant approached, in the form of its fronds and the arrangement of its fructification, to the Cyclopterids of the sub-genus Aneimites, one of which (Aneimites Acadica), from the Lower Carboniferous of Nova Scotia, I have elsewhere described as probably a tree-fern,[BH] The fronds were evidently different from those of Archæopteris[BI] a genus characteristic of the same beds, but of very different habit of growth. This accords with the fact that there is in Prof. Hall’s collection a mass of fronds of Cyclopteris (Archæopteris) Jacksoni, so arranged as to make it probable that the plant was an herbaceous fern, producing tufts of fronds on short stems in the ordinary way. The obscurity of the leaf-scars may render it doubtful whether the plant above described should be placed in the genus Caulopteris or in Stemmatopteris; but it appears most nearly allied to the former. The genus is at present, of course, a provisional one; but I have thought it only justice to the diligent labours of Mr. Lockwood to name this curious and interesting fossil Caulopteris Lockwoodi.