between the stems or branches of a dicotyledonous tree, in which the woody cylinder is associated internally with bundles of medullary tissue, and the roots of the same tree that are destitute of them. Part of a vascular bundle from the woody tissue of a Stigmaria, seen by a high power and transmitted light, is figured Plate V. fig. 6; the smooth interspaces are composed of cellular tissue.

LIGN. 29.

STEM AND ROOTS OF A SIGILLARIA.

Coal mine, near Liverpool.

a. The trunk of the tree, traversing a bed of coal.

b. The roots (Stigmariæ) spreading out in the under-clay.

This opinion of the eminent French savant, has very recently been confirmed by the discovery, at St. Helen's, near Liverpool, in Coal strata, of an

upright trunk of a Sigillaria, nine feet high, with its roots eight or nine feet in length, still attached, and extending in their natural position. These roots are undoubted Stigmaria of the usual species, S. ficoides; and the radicles, formerly considered leaves, spread out in all directions to the extent of several feet.* I have obtained no further particulars of this highly interesting discovery, and therefore insert the sketch, Lign. 29, to render it clear to the student.

I need only add, that upwards of forty species of Sigillariæ are described; and that their fossil remains have been found in every locality of the carboniferous strata.

LEPIDODENDRON (scaly-tree). See Bd. pl. 55.

Stems cylindrical, covered towards their extremities with simple, linear, or lanceolate leaves, which are attached to elevated, rhomboidal spaces, or papillæ ; papillæ marked in the upper part with a large transverse triangular scar; lower part of the stem destitute of leaves.

This is a tribe of plants whose remains abound in the coal formation, and rival in number and magnitude the Calamites and Sigillariæ above described: they are named Lepidodendra, from the imbricated or scaly appearance of their surface, occasioned by the

* From a communication to the British Association at Cork, 1843, reported in the Athenæum weekly paper.

little angular scars left by the removal of the leaves. Some of these trees have been found almost entire, from their roots to their topmost branches. One specimen, forty feet high, and thirteen feet in diameter at the base, divided towards the summit into fifteen or twenty branches, was discovered in the Jarrow coal-mine.* The foliage of these trees consists of simple, linear leaves, spirally arranged around the stem, and appears to have been shed from the base of the tree with age. The markings produced by the attachment of the leaves are never obliterated; and the twigs and branches are generally found covered with foliage, as in the specimen here figured (Lign. 30.).

The internal organization of the stems of the Lepidodendra differs from that of the Sigillariæ, in the absence of the woody cylinder and medullary rays, which constitute so peculiar and important a character in those plants. The Lepidodendra have only an eccentric, vascular, medullary zone, the interval between which and the bark is filled up by cellular tissue. In their structure, external configuration, mode of ramification, and disposition of the leaves, these trees accord so closely with the Lycopodiacea, that, notwithstanding the disparity

* Wond. p. 658. This specimen is figured and described in Foss. Flor.

+ See M. Ad. Brongniart, Archives du Muséum d'Hist. Nat. Tom. I. (for 1839) Pl. XXX.

L

in size, M. Brongniart asserts they must be considered as gigantic arborescent club-mosses.* *

* M. Corda, the able continuator of Count Sternberg's beautiful work (Flora der Vorwelt), is of opinion that the

The living species of this family amount to nearly two hundred, the greater number of which, like the ferns, inhabit the islands of intertropical regions. They are diminutive plants, with delicate foliage, none exceeding three feet in height. Most of them trail on the ground, but there are a few erect species, one of which (Lycopodium densum) is a native of New Zealand (Ly. p. 116.).

The fruit of the club-mosses is an oval or cylindrical cone, which in some species is situated at the extremity of the branches, and constitutes an imbricated spike. Now associated with the stems of the Lepidodendra, and very often imbedded in masses of their foliage, and in some instances apparently attached to the extremities of the branches, are numerous oblong, or cylindrical, scaly cones, garnished with leaves. These have received the names of Lepidostrobi (scaly-cones), and are believed to be the fruit of the trees with which they are usually collocated.

LEPIDOSTROBUS.-Cylindrical cones composed of winged scales, their axis traversed by a longitudinal cavity or receptacle, and terminating in rhomboidal disks, imbricated from above downwards.

Lepidodendra were more nearly related, both in form and structure, to the Crassulaceæ (house-leek tribe), than to the club-mosses; but we think M. Brongniart has satisfactorily shown the contrary.