The Annulariæ were small plants which floated on the surface of fresh-water lakes and ponds; their leaves were verticillate, that is, arranged in a great number of whorls, at each articulation of the stem with the branches. The Sigillariæ were, on the contrary, great trees, consisting of a simple trunk, surmounted with a bunch or panicle of slender drooping leaves, with the bark often channelled, and displaying impressions or scars of the old leaves, which, from their resemblance to a seal, sigillum, gave origin to their name. [Fig. 41] represents the bark of one of these Sigillariæ, which is often met with in coal-mines.
Fig. 42.—Stigmaria. One-tenth natural size.
The Stigmariæ ([Fig. 42]), according to palæontologists, were roots of Sigillariæ, with a subterranean fructification; all that is known of them is the long roots which carry the reproductive organs, and in some cases are as much as sixteen feet long. These were suspected by Brongniart, on botanical grounds, to be the roots of Sigillaria, and recent discoveries have confirmed this impression. Sir Charles Lyell, in company with Dr. Dawson, examined several erect Sigillariæ in the sea-cliffs of the South Joggins in Nova Scotia, and found that from the lower extremities of the trunk they sent out Stigmariæ as roots, which divided into four parts, and these again threw out eight continuations, each of which again divided into pairs. Twenty-one specimens of Sigillaria have been described by Dr. Dawson from the Coal-measures of Nova Scotia; but the differences in the markings in different parts of the same tree are so great, that Dr. Dawson regards the greater part of the recognised species of Sigillariæ as merely provisional.[43]
Two other gigantic trees grew in the forests of this period: these were Lepidodendron carinatum and Lomatophloyos crassicaule, both belonging to the family of Lycopodiaceæ, which now includes only very small species. The trunk of the Lomatophloyos threw out numerous branches, which terminated in thick tufts of linear and fleshy leaves.
Fig. 43.—Lepidodendron Sternbergii.
The Lepidodendrons, of which there are about forty known species, have cylindrical bifurcated branches; that is, the branches were evolved in pairs, or were dichotomous to the top. The extremities of the branches were terminated by a fructification in the form of a cone, formed of linear scales, to which the name of Lepidostrobus ([Fig. 45]) has been given. Nevertheless, many of these branches were sterile, and terminated simply in fronds (elongated leaves). In many of the coal-fields fossil cones have been found, to which this name has been given by earlier palæontologists. They sometimes form the nucleus of nodular, concretionary balls of clay-ironstone, and are well preserved, having a conical axis, surrounded by scales compactly imbricated. The opinion of Brongniart is now generally adopted, that they are the fruit of the Lepidodendron. At Coalbrookdale, and elsewhere, these have been found as terminal tips of a branch of a well-characterised Lepidodendron. Both Hooker and Brongniart place them with the Lycopods, having cones with similar spores and sporangia, like that family. Most of them were large trees. One tree of L. Sternbergii, nearly fifty feet long, was found in the Jarrow Colliery, near Newcastle, lying in the shale parallel to the plane of stratification. Fragments of others found in the same shale indicated, by the size of the rhomboidal scars which covered them, a still greater size. Lepidodendron Sternbergii ([Fig. 43]) is represented as it is found beneath the shales in the collieries of Swina, in Bohemia. [Fig. 46] represents a portion of a branch of L. elegans furnished with leaves. M. Eugene Deslongchamps has drawn the restoration of the Lepidodendron Sternbergii, represented in [Fig. 47], which is shown entire in [Fig. 44], with its stem, its branches, fronds, and organs of fructification. The Ferns composed a great part of the vegetation of the Coal-measure period.