Fig. 108.—Odontopteris Schlotheimii. Carboniferous, Europe and North America. Firs, and possibly by the Cycads or "false palms."[18] Amongst the "Cryptogams," there is no more striking or beautiful group of Carboniferous plants than the Ferns. Remains of these are found all through the Carboniferous, but in exceptional numbers in the Coal-measures, and include both herbaceous forms like the majority of existing species, and arborescent forms resembling the living Tree-ferns of New Zealand. Amongst the latter, together with some new types, are examples of the genera Psaronius and Caulopteris, both of which date from the Devonian. The simply herbaceous ferns are extremely numerous, and belong to such widely-distributed and
Fig. 109.—Calamites cannœformis. Carboniferous Rocks, Europe and North America. largely-represented genera as Neuropteris, Odontopteris (fig. 108), Alethopteris, Pecopteris, Sphenopteris, Hymenophyllites, &c.
[Footnote 18: Whilst the vegetation of the Coal-period was mainly a terrestrial one, aquatic plants are not unknown. Sea-weeds (such as the Spirophyton cauda-Galli) are common in some of the marine strata; whilst coal, according to the researches of the Abbé Castracane, is asserted commonly to contain the siliceous envelopes of Diatoms.]
The fossils known as Calamites (fig. 109) are very common in the Carboniferous deposits, and have given occasion to an abundance of research and speculation. They present themselves as prostrate and flattened striated stems, or as similar uncompressed stems growing in an erect position, and sometimes attaining a length of twenty feet or more. Externally, the stems are longitudinally ribbed, with transverse joints at regular intervals, these joints giving origin to a whorl or branchlets, which mayor may not give origin to similar whorls of smaller branchlets still. The stems, further, were hollow, with transverse partitions at the joints, and having neither true wood nor bark, but only a thin external fibrous shell. There can be little doubt but that the Calamites are properly regarded as colossal representatives of the little Horse-tails (Equisetaceœ) of the present day. They agree with these not only in the general details of their organisation, but also in the fact that the fruit was a species of cone, bearing "spore-cases" under scales. According to Principal Dawson, the Calamites "grew in dense brakes on the sandy and muddy flats, subject to inundation, or perhaps even in water; and they had the power of budding out from the base of the stem, so as to form clumps of plants, and also of securing their foothold by numerous cord-like roots proceeding from various heights on the lower part of the stem."
The Lepidodendroids, represented mainly by the genus Lepidodendron itself (fig. 110), were large tree-like plants, which attain their maximum in the Carboniferous period, but which appear to commence in the Upper Silurian, are well represented in the Devonian, and survive in a diminished form into the Permian. The trunks of the larger species of Lepidodendron at times reach a length of fifty feet and upwards, giving off branches in a regular bifurcating manner. The bark is marked with numerous rhombic or oval scars, arranged in quincunx order, and indicating the points where the long, needle-shaped leaves were formerly attached. The fruit consisted of cones or spikes, carried at the ends of the branches, and consisting of a central axis surrounded by overlapping scales, each of which supports a "spore-case" or seed-vessel. These cones have commonly been described under the name of Lepidostrobi. In the structure of the trunk there is nothing comparable to what is found in existing trees, there being a thick bark surrounding a zone principally composed of "scalariform" vessels, this in turn enclosing a large central pith. In their general appearance the Lepidodendra bring to mind the existing Araucarian Pines; but they are true "Cryptogams," and are to be regarded as a gigantic extinct type of the modern Club-mosses (Lycopodiaceœ). They are amongst the commonest and most characteristic of the Carboniferous
Fig. 110.—Lepidodendron Sternbergii, Carboniferous, Europe. The central figure represents a portion of the trunk with its branches, much reduced in size. The right-hand figure is a portion of a branch with the leaves partially attached to it; and the left-hand figure represents the end of a branch bearing a cone of fructification. plants; and the majority of the "spore-cases" so commonly found in the coal appear to have been derived from the cones of Lepidodendroids.
The so-called Sigillanoids, represented mainly by Sigillaria itself (fig. 111), were no less abundant and characteristic of the Carboniferous forests than the Lepidodendra. They commence their existence, so far as known, in the Devonian period, but they attain their maximum in the Carboniferous; and—unlike the Lepidodendroids—they are not known to occur in the Permian period. They are comparatively gigantic in size, often attaining a height of from thirty to fifty feet or more; but though abundant and well preserved, great divergence of opinion prevails as to their true affinities. The name of Sigillarioids (Lat. sigilla, little seals or images) is derived from the fact that the bark is marked with seal-like impressions or leaf-scars (fig. 111).