Chapter Iii, Which See.

The other forms most frequently occurring in the Carboniferous are Caulopteris, Palæopteris, and Megaphyton Stems showing merely masses of aërial roots are known by the name Psaronius.

See my "Acadian Geology," also below.

With reference to the classification of Palæozoic ferns, this has hitherto been quite arbitrary, being based on mere form and venation of fronds, but much advance has recently been made in the knowledge of their fructification, warranting a more definite attempt at classification. The following are provisional genera usually adopted:

1. Cyclopteris, Brongniart.--Leaflets more or less rounded or wedge-shaped, without midrib, the nerves spreading from the point of attachment. This group includes a great variety of fronds evidently of different genera, were their fructification known; and some of them probably portions of fronds, the other parts of which may be in the next genus.

2. Neuropteris, Brongniart.--Fronds pinnate, and with the leaflets narrowed at the base; midrib often not distinct, and disappearing toward the apex. Nervures equal, and rising at an acute angle. Ferns of this type are among the most abundant in the coal-formation.

3. Odontopteris, Brongniart.--In these the frond is pinnate, and the leaflets are attached by their whole base, with the nerves either proceeding wholly from the base, or in part from an indistinct midrib, which soon divides into nervures.

4. Dictyopteris, Gutbier.--This is a beautiful style of fern, with leaflets resembling those of Neuropteris, but the veins arranged in a network of oval spaces. Only a few species are known in the coal-formation.

5. Lonchopteris, Brongniart.--Ferns with netted veins like the above, but with a distinct midrib, and the leaflets attached by the whole base. Of this, also, we can boast but few species.

6. Sphenopteris, Brongniart.--These are elegant ferns, very numerous in species, and most difficult to discriminate. Their most distinctive characters are leaflets narrowed at the base, often lobed, and with nervures dividing in a pinnate manner from the base.

7. Phyllopteris, Brongniart.--These are pinnate, with long lanceolate pinnules, having a strong and well-defined midrib, and nerves proceeding from it very obliquely, and dividing as they proceed toward the margin. The ferns of this genus are for the most part found in formations more recent than the Carboniferous; but I have referred to it, with some doubt, one of our species.

8. Alethopteris, Brongniart.--This genus includes many of the most common coal-formation ferns, especially the ubiquitous A. lonchitica, which seems to have been the common brake of the coal-formation, corresponding to Pteris aquilina in modern Europe and America. These are brake-like ferns, pinnate, with leaflets often long and narrow, decurrent on the petiole, adherent by their whole base, and united at base to each other. The midrib is continuous to the point, and the nervures run off from it nearly at right angles. In some of these ferns the fructification is known to have been marginal, as in Pteris.

9. Pecopteris, Brongniart.--This genus is intermediate between the last and Neuropteris. The leaflets are attached by the whole base, but not usually attached to each other; the midrib, though slender, attains to the summit; the nervures are given off less obliquely than in Neuropteris. This genus includes a large number of our most common fossil ferns.

10. Beinertia, Goeppert.--A genus established by Goeppert for a curious Pecopteris-like fern, with flexuous branching oblique nervures becoming parallel to the edge of the frond.

11. Hymenophyllites, Goeppert.--These are ferns similar to Sphenopteris, but divided at the margin into one-nerved lobes, in the manner of the modern genus Hymenophyllum.

12. Palæopteris, Geinitz.--This is a genus formed to include certain trunks of tree-ferns with oval transverse scars of leaves.

13. Caulopteris, Lindley and Hutton.--Is another genus of fossil trunks of tree-ferns, but with elongate scars of leaves.

14. Psaronius, Cotta.--Includes other trunks of tree-ferns with alternate scars or thick scales, and ordinarily with many aërial roots grouped round them, as in some modern tree-ferns.

15. Megaphyton, Artis.--Includes trunks of tree-ferns which bore their fronds, which were of great size, in two rows, one on each side of the stem. These were very peculiar trees, less like modern ferns than any of the others. My reasons for regarding them as ferns are stated in the following extract from a recent paper:

"Their thick stems, marked with linear scars and having two rows of large depressed areoles on the sides, suggest no affinities to any known plants. They are usually ranked with Lepidodendron and Ulodendron, but sometimes, and probably with greater reason, are regarded as allied to tree-ferns. At the Joggins a very fine species (M. magnificum) has been found, and at Sydney a smaller species (M. humile); but both are rare and not well preserved. If the large scars bore cones and the smaller bore leaves, then, as Brongniart remarks, the plant would much resemble Lepidophloios, in which the cone-scars are thus sometimes distichous. But the scars are not round and marked with radiating scales as in Lepidophloios; they are reniform or oval, and resemble those of tree-ferns, for which reason they may be regarded as more probably leaf-scars; and in that case the smaller linear scars would indicate ramenta, or small aërial roots. Further, the plant described by Corda as Zippea disticha is evidently a Megaphyton, and the structure of that species is plainly that of a tree-fern of somewhat peculiar type. On these grounds I incline to the opinion of Geinitz that these curious trees were allied to ferns, and bore two rows of large fronds, the trunks being covered with coarse hairs or small aërial roots. At one time I was disposed to suspect that they may have crept along the ground; but a specimen from Sydney shows the leaf-stalks proceeding from the stem at an angle so acute that the stem must, I think, have been erect. From the appearance of the scars it is probable that only a pair of fronds were borne at one time at the top of the stem; and, if these were broad and spreading, it would be a very graceful plant. To what extent plants of this type contributed to the accumulation of coal I have no means of ascertaining, their tissues in the state of coal not being distinguishable from those of ferns and Lycopodiaceæ."

16. For descriptions of the genus Archæopteris and other Erian ferns, see Chapter III.