Chapter 9

SIGILLARLÆ AND STIGMARIÆ.

Among the most common and striking objects that arrest the attention of a person who visits a coal-mine for the first time, and examines the numerous vegetable relics that are profusely dispersed among the heaps of slate, coal, and shale, are long flat slabs, from half an inch to an inch thick, having both surfaces longitudinally fluted, and uniformly pitted with deep symmetrical imprints; these are disposed with such perfect regularity between the grooves, that the specimens are often supposed, by persons not conversant with palæontology, to be engraven stones, and not natural productions. These fossils are the flattened trunks of gigantic trees covered by the bark in the state of coal; the regular imprints on the surface, being the scars left by the separation of the petioles or leaf-stalks, as in the arborescent ferns previously examined. The nameSigillaria, commonly applied to these fossils, is derived fromsigillum, a seal, and alludes to the regular and uniform pattern of the imprints on the surface. These stems are from a few inches to several feet in diameter, and the largest attain a height of sixty feet; they are generally found lying in a horizontal position in the strata, and quite flat, from the pressure produced by the superincumbent rocks; but when the trunks are in an erect position, and at right angles to the plane of the beds, the cylindrical form of the original is preserved.

A remarkable instance, in which five stems of Sigillaria were standing upright, with their roots in the soil below, apparently in the position in which they grew, was brought to light a few years since, in forming the Bolton and Manchester railway.[94]They stand on the same plane, and nearto each other. Their roots are branched, and spread out in the bed of impure coal in which they are implanted. The trunks are surrounded by a soft blue shale. The largest tree is eleven feet high, and seven and a half feet in circumference at the base; its trunk is gnarled and knotted, and has many decorticated prominences, like those in barked timber of our old dicotyledonous trees; the roots, too, partake of the same character.[95]The others are respectively from three to five feet in height. A sketch of one of the short stems is subjoined. All the trees were broken off as if by violence, and no traces of the upper part of the stems or branches were detected.

[94]These trees still remainin situ, and, thanks to the scientific zeal of Mr. Hawkshaw, have been carefully preserved. They are situated at Dixon Fold, Clifton, near Manchester. Instructive models of these highly interesting relics of the carboniferous forests may be obtained.An excellent Memoir on this discovery, with illustrations, by Mr. Hawkshaw, is given in Geol. Trans, vol. vi. pl. xvii. See Pict. Atlas, p. 198; and Petrifactions, p. 36.

An excellent Memoir on this discovery, with illustrations, by Mr. Hawkshaw, is given in Geol. Trans, vol. vi. pl. xvii. See Pict. Atlas, p. 198; and Petrifactions, p. 36.

[95]See Mr. Bowman's Memoir, Geol. Proc. vol. iii. p. 270.

Lign. 32. Base of a Trunk of a Sigillaria. with roots,standing erect with five other stems, in Carboniferous strata.(The original is four feet high.)

In the stratum through which the roots extend, a considerable quantity of the fossil cones, calledLepidostrobi, hereafter described, were imbedded (seeLign.40). A thin layer of coal which invested the stems, was evidently thecarbonized bark. All the stems were filled with blue clay, or shale, a proof that they were hollow when submerged in the mud, which is now consolidated into the shale in which they are imbedded. But it is not probable that they were originally tubular, like a reed: on the contrary, there is evidence to show that they were highly organized. Their internal structure may have decayed, or been destroyed by insects or other depredators; as is often the case in tropical climates, where the trunks of timber trees are speedily excavated after their fall, and afford shelter to innumerable insects and reptiles, as the weary traveller often finds to his surprise and annoyance.[96]The late Mr. Bowman affirmed[97]that these trees were dicotyledonous, and stated that medullary rays and coniferous structure could be detected; an opinion, which the researches of M. Brongniart on the Sigillariæ have fully corroborated.

[96]Mr. Hawkshaw, Geol. Proc. p. 269.[97]Geol. Proc. vol. iii. p. 270.

[96]Mr. Hawkshaw, Geol. Proc. p. 269.

[97]Geol. Proc. vol. iii. p. 270.

ERECT STIGMARIÆ.

Many other instances have been noticed of Sigillariæ standing more or less erect in the strata. In forming the railway tunnel at Claycross, five miles south of Chesterfield, through the middle portion of the Derbyshire coal-measures, in 1838, a group of nearly forty trees (Sigillariæ) was discovered, standing not more than three or four feet apart, at right angles to the plane of the strata.[98]On the coast of Northumberland, within the length of half a mile, twenty trees were observed by Mr. Trevelyan, in 1816 (Bd.p. 470). The coal-pit at St. Etienne, in France, described by M. Alex. Brongniart, is celebrated for affording an example of this phenomenon (Wond.p. 673); but the positions of many of those stems are inclined at various angles, and their roots implanted in different beds, so that the perpendicularity of the erect trees is probably accidental (Bd.p. 471).

[98]Ibid. p. 272.

The most remarkable instance hitherto observed, is on thesouthern shore of the Bay of Fundy, in Nova Scotia, where the cliffs, which are about two hundred feet high, are composed of carboniferous strata, consisting of coal, clay, grit, and shale, in which numerous erect trees, probably Sigillariæ, are seen on the face of the cliff; there are ten rows one above another, indicating, in the opinion of Sir C. Lyell, repeated subsidences of the land, so as to allow of the growth often successive forests![99](Wond.p. 674).

[99]"On the Coal Strata of Nova Scotia." Amer. Journ. Oct. 1841 and Travels in America, vol. ii. p. 180.

Lign. 33. Sigillariæ;in Coal-shale.Fig.1.—A specimen deprived of its carbonaceous bark, except in the interstices of the channels, and showing pits left by the external scars.2.—The markings ofS. Defrancii. (Vég. Foss. Br.)

SIGILLARLÆ.

The stems of Sigillariæ vary in size from a few inches to five feet in diameter; and in length from five to sixty feet; they gradually taper from the base to the summit. A specimen measured by M. Brongniart was forty feet long, one foot in diameter at the base, and but six inches at the top, where it divided into two equal branches. These stems may be readily distinguished from those of other trees withwhich they are associated, by the fluted surface produced by the deep longitudinal grooves, and the regularly disposed imprints between the channels.[100]The carbonized bark, in large specimens, is often an inch thick, but in small examples is a mere pellicle, and being extremely brittle, flakes off with the slightest touch, leaving the inner surface exposed, with the coal remaining in the deep furrows and pits, as inLign. 33, fig. 1. No traces of leaves, or fruit, in connexion with the stems, have been observed. The subjoined sketches (Lign.33, and34,) illustrate the usual aspect of these fossils. The difference between the imprints on the outside of the bark, and those on the exposed surface of the stem, from the removal of the cortical covering, is well marked inLign. 34.

[100]The stems of some recent dicotyledonous trees from New Zealand, in the possession of Dr. Robert Brown, possess similar longitudinal ribs and furrows, both on the bark and alburnum, or naked wood.

Lign. 34. Sigillaria Saullii.Carb. Manchester.a.The imprints of the petioles on the external surface of the carbonized cortical investment.b.The inner surface, exposed by the removal of the crust or bark.

Internal Structure of Sigillariæ.—Our knowledge of the structure of this numerous tribe of plants, has received an important accession by the discovery of the silicified fragment of a stem, which, fortunately for the advancement of science, was placed at the disposal of M. Adolphe Brongniart. It has been described and illustrated by that eminent botanist, in a memoir which is one of the most valuable contributions to fossil botany that has hitherto appeared.[101]

[101]The reader intending to make fossil botany his particular study, should refer to the original memoir, and become familiar with the facts and inferences so admirably enunciated by the author; not only for the illustration of the structure of the tribe of plants under consideration, but as a valuable exemplification of the manner in which all such inquiries should be conducted. SeeArchives du Muséum d'Histoire Naturelle, tom. i. Paris, 1839.

Lign. 35. Silicified Stem of Sigillaria elegans.Autun. France.(M. Adolphe Brongniart.)Fig.1.—A transverse section of the silicified stem, from Autun;nat.a.Situation of the medullary tissue, occupied by coloured silex.b.Zone composed of bundles of vessels, forming the woody tissue.c.Band of cellular tissued.Space between the ligneous cylinder and the bark, with no evident structure, but originally occupied by the external cellular tissue.e.Zone of indistinct cellular substance.f.External cortical envelopment, or bark.2.—Portion of one of the vessels of the medullary tissue, as seen in a longitudinal section, (× ×.)3.—Portion of a spiral vessel of the same tissue. (× ×.)

Autun. France.(M. Adolphe Brongniart.)

The annexed figure (Lign.35) is an outline of the specimen, of the natural size; but this sketch is a mere plan ordiagram, for it is impossible without the aid of colour to convey a faithful idea of the original. The student should observe, that when mineral matter has permeated the stems of plants, the vascular tissue is often so well preserved, that one such specimen affords more important information, than hundreds of examples in which the form alone remains.

SIGILLARLA ELEGANS.

The external surface of this specimen possesses the characteristic markings of the insertion of the leaf-stalks ofSigillaria elegans. The internal organization, as seen in the transverse section, is as follows:—

a.The centre, filled with silex; it exhibits no traces of structure.

b.The zone which surrounds the interspace on which this letter is placed, is composed of bundles of vascular tissue. A portion of one of these bundles, highly magnified, is represented inPlate V. fig. 7.

Theinnercircle of this zone, indicated by theconvex undulating line, is made up of medullary vascular tissue; the external circle is divided by rays, and is composed of woody fibre, constituting a ligneous cylinder. One of the spiral vessels (fig. 3), and another showing a remarkable difference of structure in a short space (fig.2), as seen in a longitudinal section of the medullary tissue, are figured inLign.35.

The ligneous cylinder is surrounded by a band of cellular tissue, and the space between this and the cortical integument is occupied by silex, in which there are but obscure traces of structure.

The inner layer of bark,f, is composed of elongated cells,disposed in a radiating manner, and traversed by fibro-vascular bundles, which pass towards the leaves.

Upon instituting a comparison between the fossil and the stems of those recent plants which present the closest analogy to it, M. Brongniart was led to conclude that the Sigillariæ constituted a peculiar extinct family, belonging to the great division of gymnospermous dicotyledons.

The Sigillariæ were tall erect trees, with a regular and cylindrical stem, without side branches, but dichotomous towards the summit. Their superficial bark was hard and durable, channelled longitudinally, bearing leaf-scars that are of a rounded form above and below, and angular at the sides, often oblong in relation to the stem, and having three vascular pits, one central and small, and two lateral of a larger size. The internal structure bears most analogy to that of the Cycadeæ, and the foliage consisted of long linear carinated leaves. The Sigillariæ, therefore, differ essentially from the arborescent cryptogamia, which they somewhat approach in having scalariform vascular tissue, symmetrical and regular leaf-scars, and branchless trunks. More than fifty species have been determined.[102]

[102]For figures of Sigillariæ, see Pictorial Atlas, pl. xix. xx, xxiv.

STIGMARIA.

Stigmaria.Lign. 36.—This extended notice of the structure of the Sigillariæ,.will enable us to understand the nature of the fossil vegetables termed Stigmariæ, or spotted-stems, which abound in the beds of under-clay of most coal-fields, as stated in a former part of this work (ante,p. 81.). These bodies when uncompressed are of a cylindrical form, from one to six or seven inches in diameter, and of considerable length—sometimes upwards of twenty feet—and gradually diminish in size towards their termination. The surface is marked with distinct pits or areolæ, of a circular or oval form, with a small tubercle in the centre of each, disposed around the stem in a quincunx and somewhat regular order.When broken transversely, a small cylindrical axis is seen to extend in a longitudinal direction through the stem, like a medullary column; it seldom occupies the centre, but lies near to one side, and parallel with a depression on the outer surface of the fossil. This internal body is often loose, and removable; its surface is covered with interrupted, irregular, longitudinal, ridges, which leave corresponding depressions on the walls of the cavity in which it was inclosed.Lign.36, represents a fragment exhibiting the characters above described.

Lign. 36. Stigmaria ficoides.Carboniferous. Derbyshire.—1/4nat.Fig.1.—Portion of a stem, with some of the rootlets (formerly considered as leaves) extending into the surrounding clay. The internal axis is seen ata; and the corresponding groove on the portion of external surface that remains.2.—An outline of one of the rootlets, with a tubercle to show the mode of its attachment by a ball and socket joint to the root.

When Stigmariæ are observed in the under-clay, to which stratum they are principally confined, long, tapering, subcylindrical fibres, often several feet in length, are seen affixed to the tubercles with which the surface is covered; their form and mode of attachment are shown inLign.36. Instances occur in which several Stigmariæ spring from a common centre, of a dome-like form, whence they radiate in every direction (Bd.pl. lvi.fig.8), and the main branches divide and subdivide till they are lost in the surrounding rock.

The nature of these fossil vegetables was long a perplexing question, for no specimens had been found in connexion with any of the stems, branches, or foliage, that abound in the coal deposits. At length, the discovery of a dome-shaped mass, to which were attached numerous Stigmariæ, seemed to afford a clue to the solution of this botanical problem; and it was concluded by the eminent authors of the "Fossil Flora of Great Britain," that the original belonged to a tribe of plants which inhabited swamps, or still and shallow lakes, and were characterized by a low truncated stem, having long horizontal branches beset with cylindrical, and, probably, succulent leaves, that either trailed on the surface of the swamp, or floated in the water.

But within the last few years, the occurrence in various carboniferous deposits of erect stems of Sigillariæ, has shown that the Stigmariæ are nothing more than the roots of these and other congenerous trees; an opinion maintained by the Rev. H. Steinhaur more than thirty years ago, and subsequently affirmed by M. Adolphe Brongniart, who found, on examining microscopically the internal structure of a silicified specimen in which the vascular tissue was preserved, that it bore as close an analogy to that of the Sigillariæ, as exists between the roots and trunks of certain dicotyledonous trees.

The annexed figure,Lign.37, represents the transverse section of a small Stigmaria, with the axis displaced from its natural situation; this circumstance, as well as the corresponding external groove, has arisen from compression, by which the tough cylinder has been forced from its original position in the middle of the soft cellular tissue, to one side.

Lign. 37. Transverse Section of Stigmaria ficoides;nat.(M. Adolphe Brongniart.)This specimen shows that the cylinder (ainLign.36) is formed of bundles of vascular tissue, disposed in rays.

The central axis is thus shown to be a cylinder composed of bundles of vessels, disposed in a radiating manner, and separated from each other by medullary rays; the whole constituting a ligneous zone resembling that of Sigillaria (seeLign.35); but the inner circle of medullary tissue seen in the latter is altogether wanting. This difference is similar to that observable in 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, seenby a high power and transmitted light, is figuredPl. V. fig. 6; the smooth interspaces are composed of cellular tissue.

Lign. 38. Erect Stem of a Sigillaria, with roots.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.

ERECT SIGILLARLA WITH ROOTS.

This opinion of M. Brongniart was confirmed by the discovery, in 1843, at St. Helen's, near Liverpool, of an upright trunk of a Sigillaria, nine feet high, with ten roots eight or nine feet in length, still attached, and extending in their natural position.These roots are undoubted Stigmariæ of the usual species, S. ficoides; and the radicles, formerly considered leaves, are spread out in all directions, to the extent of several feet.[103]To the sagacity and perseverance of Mr. Binney, of Manchester, science is indebted for this importantdiscovery; the same gentleman laid bare, on the floor of the mine at Dunkinfold, near Manchester, a large erect trunk of a Sigillaria, with numerous Stigmariæ roots.

[103]From a communication to the British Association at Cork, 1843.

In the Pictou coal-field of Cape Breton, in Nova Scotia, similar facts have been brought to light; the remarkable phenomena existing in that locality, of successive carboniferous deposits containing scores of erect trees with roots spreading into their native soil, presenting peculiar facilities for verifying the observations made in England. In an interesting memoir on the coal-fields of Nova Scotia, Mr. Richard Brown has given a detailed account of numerous examples of stems of Sigillariæ, and of Lepidodendra, (a tribe of gigantic club-mosses of which we shall presently treat,) with the roots attached; these roots, in every instance, had the characters and structure of Stigmariæ. In one instance, the stem of the tree was broken off close to the roots, and the hollow cylinder of bark was bent down and doubled over by the pressure of the surrounding mud, so as effectually to close up the aperture, and leave only a few irregular cicatrices converging near the apex; this fossil explains the true nature of the "dome-shaped" plant figured in the Fossil Flora, and in Dr. Buckland's Essay.[104]

[104]See Pictorial Atlas, p. 200: and Petrifactions, pp. 37, 38.

LEPIDODENDRON.

Lepidodendron(scaly-tree).Lign. 39.—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.

Lign. 39.Fig.1.—A terminal Branch of a Lepidodendron;nat.2.—Leaf-scars on the stem of a Lepidodendron;nat.In Coal-shale, Newcastle.

In Coal-shale, Newcastle.

The remains of this tribe of plants abound in the coal formation, and rival in number and magnitude the Calamites and Sigillariæ previously described. These trees have received the name ofLepidodendra, from the scaly character of their stems, occasioned by the angular scars left by the separation of the foliage, as is the case in arborescent ferns: the term, however, simply indicates the appearance, for the surface is not imbricated. Some of these trees have been found almost entire, from the roots to their topmostbranches. 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.[105]The foliage 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 scars produced by the attachment of the petioles were persistent; and the twigs and branches are generally found covered with foliage, as inLign.39. The roots are Stigmariæ, like those of the Sigillariæ, as proved by specimens in the Pictou coal-field, discovered by Mr. Brown.[106]

[105]Wond, p. 722. This specimen is figured and described in Foss. Flor.[106]Petrifactions, p. 39.

[105]Wond, p. 722. This specimen is figured and described in Foss. Flor.

[106]Petrifactions, p. 39.

The internal organization of the stem of Lepidodendron differs from that of Sigillaria, in the absence of the woody cylinder and medullary rays which constitute so peculiar and important a character in the latter. The Lepidodendra have only an eccentric, vascular, medullary zone, the interval between which and the bark is filled up by cellular tissue.[107]In their structure, external configuration, mode of ramification, and disposition of the leaves, they accord so closely with theLycopodiaceæ, that, notwithstanding the disparity in size, M. Brongniart, Dr. Joseph Hooker, and other eminent botanists, concur in regarding them as gigantic arborescent club-mosses[108]The living species of Lycopodiaceæ amount to nearly two hundred, the greater number of which, like the arborescent ferns, inhabit the islands of intertropical regions. They are diminutive plants, with delicate foliage, none exceeding three feet in height; mostof them trail on the ground, but there are a few erect species, one of which (Lycopodium densum) is abundant in New Zealand.

[107]See M. Ad. Brongniart, Archives du Museum d'Hist. Nat. torn. i. (for 1839), pl. XXX.[108]Figures of Lepidodendra inWond.p. 718. Pict. Atlas, pl. i. iii. ix. xxvi. xxvii. xxxiii.

[107]See M. Ad. Brongniart, Archives du Museum d'Hist. Nat. torn. i. (for 1839), pl. XXX.

[108]Figures of Lepidodendra inWond.p. 718. Pict. Atlas, pl. i. iii. ix. xxvi. xxvii. xxxiii.

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 in masses of their foliage, and in some instances attached to the extremities of the branches, are numerous oblong, or sub-cylindrical, scaly cones, garnished with leaves. These have received the names ofLepidostrobi(scaly-cones), and are unquestionably the fruit of the trees with which they are imbedded.

LEPIDOSTROBUS.

Lepidostrobus.Lign. 40.—A cylindrical strobilus or cone, imbricated from above downwards, composed of winged scales, terminating in rhomboidal discs: the axis traversed by a longitudinal cavity or receptacle.

These fossils have long been known to collectors, and are figured by Martin (Petrif. Derbiensia), Parkinson (Org. Rem.vol. i. pl. ix.), and others. They are cylindrical imbricated bodies, rounded at both extremities, from two to six or seven inches in length, and one or two inches in circumference. When broken asunder, a cylindrical cavity is exposed, which is sometimes hollow, but commonly filled with mineral matter; and when specimens are found imbedded in shale, the cone is fringed with linear-lanceolate bracteæ, as inLign. 40, fig. 3. These fruits, like the fronds of ferns, often form the nuclei of ironstone nodules, and the leaves are frequently replaced either by a white hydrate of alumine, or by the mineral called galena, or sulphuret of lead, and the receptacles filled with the same substances. The specimens from Coalbrook Dale are generally in this state of mineralization, and possess great brilliancy; they are interesting examples of the electro-chemical changeswhich these fruits of the carboniferous forests have undergone.[109]

[109]These fossil cones are not liable to decompose, like the pyritous fruits from the Isle of Sheppey; they require no preparation for the cabinet; washing injures their lustre; a soft brush will safely remove any extraneous matter. There is a fine collection of Lepidostrobi in the British Museum; see Petrifactions, p. 42.

Lign. 40. Lepidostrobi, the fruit of Lepidodendra;nat.Coalbrook Dale.Fig.1.—A portion of a cone, showing the imbricated structure and internal cavity.2.—The upper part of a cone, displaying the imbricated surface.3.—A young specimen attached to the extremity of a branch.

The figures inLign.40, represent the usual characters of these fruits. Of the young specimen, (fig. 3,) situated at the termination of a branch, M. Brongniart observes, "qu'il est impossible de ne pas reconnaître pour un Lepidostrobusjeune, fixé à l'extrémité d'un rameau."[110]As it is only in their young state that the spikes are found attached to the branches, it is probable they were shed as soon as they arrived at maturity.

[110]Hist. Vég. Foss. tom. ii. p. 47.

Triplosporite.—Additional light has recently been thrown on the structure of the Lepidostrobi, by Dr. Robert Brown's examination of a silicified specimen of the upper part of a strobilus, in which the internal organization is beautifully displayed. The reader specially interested in this department of fossil botany should refer to the original memoir by the illustrious President of the Linnæan Society, with the accompanying plates that admirably exhibit the microscopic analysis of the structure of this remarkable fossil; a slice of which was shown me some years since by the late Marquis of Northampton.[111]The external surface of the specimen is covered with hexagonal areolæ; the transverse sections exhibit the appearance of the bracteæ and sporangia. The strobilus is formed of a central axis of relatively small diameter, from which proceed bracteæ, about thirteen in number, that are densely approximated, and much imbricated; and of an equal number of sporangia, filled with innumerable microscopic sporules, originally connected in threes. This triple composition of sporules (which differs from the constant quadruple union in the tribes of existing plants presumed to be most nearly allied to the fossil, namely theOphioglosseæandLycopodiaceæ) is expressed by the nameTriplosporite, adopted by Dr. Brown to indicate this peculiarity of structure, and the class or primary division to which the original plant is supposed to belong.[112]

[111]The specimen brought to England was but two inches of the upper end of the cone; it was purchased conjointly by Lord Northampton, Dr. Brown, and the British Museum, for 30l.![112]See Trans. Linnæan Society of London, vol. xx. p. 469.

[111]The specimen brought to England was but two inches of the upper end of the cone; it was purchased conjointly by Lord Northampton, Dr. Brown, and the British Museum, for 30l.!

[112]See Trans. Linnæan Society of London, vol. xx. p. 469.

Lycopodites.—Species of true Lycopodiaceæ occur in tertiary marls; a beautiful specimen, from Germany,LycopoditesBenettiæ, is figuredWond.p. 723.

HALONIA. KNORRIA.

Halonia; Knorria.Lign. 41.—Associated with the plants already described from the coal-measures, there are trunks and branches of other trees, presenting peculiar and but imperfectly known characters, which it will be convenient to notice in this place. Fragments of these stems are to be seen in most public collections of the carboniferous flora, and should be examined by the student, for figures and descriptions can convey but an imperfect idea of their nature.

Mr. Denny, the intelligent and indefatigable Curator of the Leeds Philosophical Society, has given the following admirable summary of the distinctive characters of the stems of most frequent occurrence in the Coal,[113]which will be found a useful guide to the collector.

[113]On the Fossil Flora of the Carboniferous Epoch, with especial reference to the Yorkshire Coal-field. By Mr. Henry Denny, A.L.S. Proceedings of the Polytechnic Society of Yorkshire; for 1850.

1.Sigillaria.—Stem furrowed, not branched, leaf-scars small, round, much narrower than the ridges of the stem.

2.Favularia.—Stem furrowed, not branched, leaf-scars small, square, and as broad as the ridges of the stem.

3.Lepidodendron.—Stem not furrowed, branched, covered with lozenge-shaped scars in quincuncial order, each having a papilla in the upper part; the upper portion of the stem and branches with simple linear leaves; the lower portion destitute of leaves.

4.Halonia.—Stem not furrowed, branched, covered with indistinct rhomboidal marks, and tubercular projections disposed in quincunx.

5.Knorria.—Stem not furrowed, branched, marked with projecting scars of petioles disposed spirally.

6.Megaphyton.—Stem dotted, neither furrowed nor branched, leaf-scars very large, of a horse-shoe figure.[114]

[114]Pictorial Atlas, pl. xxv.

7.Bothrodendron.—Stem pitted, neither furrowed nor branched, scars of cones (?) obliquely oval.

8.Ulodendron.—Stem neither furrowed nor branched, covered with rhomboidal marks; scars of cones (?) circular.

The characters of the roots called Stigmariæ (ante,p. 134.), and of the stems namedCalamities(ante,p. 107.), andEquisetites(ante,p. 106.), are sufficiently distinct from the above to be easily recognized, I will briefly notice those not previously described.

Lign. 41. Stems from the Coal Formation.Fig.1.—Halonia regularis.Coalbrook Dale.2.—Knorria Taxina.Roof of the High-main Coal seam, Jarrow Colliery.(Brit. Foss. Flor.)

Halonia.—The specimens usually seen are mere sandstone casts having a thin carbonaceous crust; the stem is branched and beset with large elevated knobs, or subcortical protuberances, as shown infig. 1, Lign. 41. Theseplants appear to be closely related to the Lepidodendra; their mode of branching is shown in a beautiful specimen (in the museum of the Leeds Philos. Soc.) figured and described by Mr. Denny, which is also remarkable because it indicates the probability that the Haloniæ, and the fossil stems, termed Knorriæ, are identical; for the specimen in question, which in its branches is unquestionably of the former type, has the base of the stem impressed with the leaf-scars of the latter.

Knorria.—To this genus the authors of the Fossil Flora of Great Britain referred those stems which have projecting leaf-scars, arranged spirally. The beautiful specimen figured asKnorria taxina,Lign. 41, fig. 2, closely resembles a young branch of Yew (Taxus), and perhaps might be more correctly namedTaxites.

Bothrodendron and Ulodendron.—These genera, together withMegaphyton, are stems of a very remarkable character, and are easily distinguished by the vertical rows of large and distant scars. The two first have two series of very deep oval depressions on opposite sides of the stems, arranged alternately in the specimens I have examined: from the size and form of these obliquely-oval cavities, it is supposed that they were formed by the attachment of cones, and not by petioles; but their real nature is involved in obscurity.[115]

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