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the stems, had undergone decomposition, during the interval in which they were floating between their place of growth, and that of their final submersion.

M. Ad. Brongniart enumerates forty-two species of Sigillaria, and considers them to have been nearly allied to arborescent Ferns, with leaves very small in proportion to the size of the stems, and differently disposed from those of any living Ferns. He would refer to these stems many of the numerous fern leaves of unknown species, which resemble those of existing arborescent genera of this family. Lindley and Hutton show reasons for considering that Sigillariæ were Dicotyledonous plants, entirely distinct from Ferns, and different from any thing that occurs in the existing system of vegetation.*

Favularia. Megaphyton. Bothrodendron.. Ulodendron.†

The same group of fossil plants to which Lindley and Hutton have referred the genus Sigillaria, contains four other extinct genera, all of which exhibit a similar disposition of scars arranged in vertical rows, and indicating. the places at which leaves, or cones, were attached to the trunk. The names of these are Favularia, Megaphy

* "There can be no doubt," say they, (Foss. Flora, vol. i. p. 155) "that as far as external characters go, Sigillaria approached Euphorbia and Cacteæ more nearly than any other plants now known, particularly in its soft texture, in its deeply channelled stems, and what is of more consequence in its scars, placed in perpendicular rows between the furrows. It is also well known that both these modern tribes, particularly the latter, arrive even now at great stature; farther, it is extremely probable, indeed almost certain, that Sigillaria was a dicotyledonous plant, for no others at the present day have a true separable bark. Nevertheless, in the total absence of all knowledge of the leaves and flowers of these ancient trees, we think it better to place the genus among other species, the affinity of which is at present doubtful."

t Pl. 56, Figs. 3. 4. 5. 6. 7..

ton, Bothrodendron, Ulodendron.*

Our figures Pl. 56,

Figs. 3, 4, 5, 6, represent portions of the trunk and scars of some of these extraordinary Coniferæ.

Among existing vegetables, there are only a few succulent plants which present a similar disposition of leaves, one exactly above another in parallel rows; but in the fossil Flora of the Coal formation, nearly one-half, out of eighty known species of Arborescent plants, have their leaves growing in parallel series. The remaining half are Lepido

* The genera composing this group are thus described, Foss, Flora, vol. ii. p. 96.

1. Sigillaria. Stem furrowed. Scars of leaves small, round, much narrower than the ridges of the stem. See Pl. 56, Figs. 1, 2, 2'.

2. Favularia. Stem furrowed. Scars of leaves small, square, as broad as the ridges of the stem. See Pl. 56, Fig. 7.

Scars of leaves very large,

3. Megaphyton. Stem not furrowed, dotted.
of a horse-shoe figure, much narrower than the ridges.

4. Bothrodendron. Stem not furrowed, covered with dots. Scars of cones, obliquely oval.

5. Ulodendron. Stem not furrowed, covered with rhomboidal marks, Scars of cones circular. See Pl. 56, Figs. 3, 4, 5, 6, 6'.

In the first three genera of this group, the scars appear to have given origin to leaves; in the latter two they indicate the insertion of large cones.

In the genus Favuluria (Pl. 56, Fig. 7) the trunk was entirely covered with a mass of densely imbricated foliage, the bases of the leaves are nearly square, and the rows of leaves separated by intermediate grooves; whilst in Sigillaria the leaves were placed more loosely, and at various intervals in various species. (Foss. Flora, Pl. 73. 74. 75.)

In the genus Megaphyton the stem is not furrowed, and the leaf scars are very large, and resemble the form of horse-shoes disposed in two vertical rows, one on each side of the trunk. The minor impressions resembling horse-shoes, in the middle of these scars, appear to indicate the figure of the woody system of the leaf-stalk. (Foss. Flora, Pl. 116, 117.)

In the genus Bothrodendron (Foss. Flora, Pl. 80, 81) and the genus Ulodendron, (Foss. Flora, Pl. 5. 6.) the stems are marked with deep oval or circular concavities, which appear to have been made by the bases of large cones. These cavities are ranged in two vertical rows, on opposite sides of the trunk, and in some species are nearly five inches in diameter. (Pl. 56. Figs. 3. 4. 5. 6.)

dendra, or extinct Coniferæ. (See Lindley and Hutton, Foss. Flora, vol. ii. p. 93.)

Stigmaria.*

The recent discoveries of Lindley and Hutton have thrown much light upon this very extraordinary family of extinct fossil plants. Our figure, Pl. 56, Fig. 8, copied from their engraving of Stigmaria ficoides, (Foss. Flora, Pl. 31, Fig. 1) represents one of the best known examples of the genus.†

The centre of the plant presents a dome-shaped trunk or stem, three or four feet in diameter, the substance of which was probably yielding and fleshy; both its surfaces were slightly corrugated, and covered with indistinct circular spots. (Pl. 56, Figs. 8. 9.)

From the margin of this dome there proceed many horizontal branches, varying in number in different individuals from nine to fifteen; some of these branches become forked at unequal distances from the dome; they are all broken off short, the longest yet found attached to the stem, was four feet and a half in longth. The extent of these branches, when outstreched and perfect, was probably from twentyto thirty feet. The surface of each branch is covered with

* Pl. 56, Figs. 8. 9. 10. 11.

+ Seventeen specimens of this kind have been found within the space of 600 square yards, in the shale covering the Bensham seam of coal at Jarrow Colliery near Newcastle, at the depth of 1200 feet.

It appears from sections of a branch of Stigmaria, engraved by Lindley and Hutton, (Foss. Flora, Pl. 166,) that its interior was a hollow cylinder composed exclusively of spiral vessels, and containing a thick pith, and that the transverse section exhibits a structure something like that of Coniferæ, but without concentric circles, and with open spaces instead of the muriform tissue of medullary rays. No such structure is known among living plants. These cylindrical branches are usually depressed on one side, probably the inferior side (Pl. 56, Figs. 8. ab. and 10. b.;) adjacent to this depress

spirally disposed tubercles, resembling the papillæ at the base of the spines of Echini. From each tubercle there proceeded a cylindrical and probably succulent leaf; these extended to the length of several feet from all sides of the branches. (Pl. 56, Figs. 10. 11.) The leaves, usually, in a compressed state, are found penetrating in all directions into the sand-stone or shale which forms the surrounding matrix; they have been traced to the length of three feet, and have been said to be much longer.*

In many of the strata that accompany the coal, fragments of these plants occur in vast abundance; they have been long noticed in the sand-stone called Gannister and Crowstone, in the Yorkshire and Derbyshire coal fields, and have been incorrectly considered to be fragments of the stems of Cacti.

The discovery of the dome-shaped centres above described, and the length and forms of the leaves and branches render it highly probable that the Stigmariæ were aquatic plants, trailing in swamps, or floating in still and shallow lakes, like the modern Stratiotes and Isoetes. From such situations they may have been drifted by the same inundations, that transported the Ferns and other land vegetables, with which they are associated in the coal formation. The form of the trunk and branches shows that they could not have risen upwards into the air; they must therefore either have trailed on the ground, or have floated in water. The

sion there is found a loose internal eccentric axis, or woody core (Pl. 56. Fig. 10. a.) surrounded with vascular fasciculi that communicated with the external tubercles, and resembled the internal axis within the stems of certain species of Cactus.

* All these are conditions, which a Plant habitually floating with the leaves distended in every direction, would not cease to maintain, when drifted to the bottom of an Estuary, and there gradually surrounded by sediments of mud and silt.

† The place and form of the leaves, supposing them to have grown on all sides of branches suspended horizontally in water, would have been but little changed by being drifted into, and sinking to the bottom of, an

Stigmaria was probably dicotyledonous, and in its internal structure seems to have borne some analogies to that of the Euphorbiacea.

Conclusion.

Besides these Genera which have been enumerated, there are many others whose nature is still more obscure, and of which no traces have been found among existing vegetables, nor in any strata more recent than the Carboniferous series.* Many years must elapse before the character of these various remains of the primeval vegetation of the Globe can be fully understood. The plants which have contributed most largely to the highly-interesting and important formation of Coal, are referable principally to the Genera whose history we have attempted briefly to elucidate: viz. Calamites, Ferns, Lycopodiaceæ, Sigillariæ, and Stigmariæ. These materials have been collected chiefly from the carboniferous strata of Europe. The same kind of fossil plants are found in the coal mines of N. America, and we have reason to believe that similar remains occur in Coal formations of the same Epoch, under very different Latitudes, and in very distant quarters of the Globe, e. g. in India, and New Holland, in Melville Island, and Baffin's Bay.

The most striking conclusions to which the present state of our knowledge has led, respecting the vegetables which gave origin to coal are, 1st, that a large proportion of these plants were vascular Cryptogamiæ, and especially Ferns;

estuary or sea, and there becoming surrounded by sediments of mud or sand. This hypothesis seems supported by the observations made at Jarrow, that the extremities of the branches descend from the dome towards the adjacent bed of coal.

* Some of the most abundant of these have been classed under the names of Asterophyllites, (see Pl. 1, Figs. 4. 5.) from the stellated disposition of the leaves around the branches.

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