Chapter VI: Fossil Vegetables (2)

An excellent work ("_Dendrolithen_") on these fossils, in which thirty species are described, has been published at Dresden by M. Cotta; who arranges them under the genus _Psaronius_ or _Psarolites_. The stem is composed of two distinct parts; an outer zone, consisting of a great number of nearly cylindrical bundles of vessels, supposed to have been roots which proceeded from the stem near its base; and an inner part or axis. In the outer portion, the fossil _air-roots_ have a vascular tissue, but there is often a delicate cellular tissue interposed. In the axis the vessels form zigzag or wavy bands, resembling those of ferns.[90] These flexuous and vermiform bands are entirely composed of barred or scalariform vessels, similar to those of ferns and club-mosses. The Psarolites are therefore considered by M. Ad. Brongniart to be the bases of the trunks of lycopodiaceous trees, while M. Cotta and other botanists regard them as true arborescent ferns.[91]

[90] Pict. Atlas, pl. viii.

[91] See M. Brongniart's "_Tableau des Genres de Végét. Foss._" p. 44.

Dr. Buckland has discovered in the New Bed sandstone formation at Allesley, near Coventry, silicified trunks of coniferous trees, and it is not improbable that further research in that locality may bring to light fern-stems like those of Chemnitz.[92] Dr. Lloyd, of Warwick, has recently obtained leaves of several coniferæ from the same locality.[93]

[92] Vide Geol. Proc. vol. ii. p. 438.

[93] Geol. Society, June 1852. Dr. Lloyd's specimens are probably referable to the genus _Walchia_: see _Lign. 60._

[Sidenote: SIGILLARLÆ AND STIGMARIÆ.]

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 name _Sigillaria_, commonly applied to these fossils, is derived from _sigillum_, 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 near to 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 remain _in 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.

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

(_The original is four feet high._)]

In the stratum through which the roots extend, a considerable quantity of the fossil cones, called _Lepidostrobi_, hereafter described, were imbedded (see _Lign. 40_). A thin layer of coal which invested the stems, was evidently the carbonized 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.

* * * * *

[Sidenote: 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 the southern 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.

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 of S. Defrancii. (_Vég. Foss. Br._)
]

[Sidenote: 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 with which 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 in _Lign. 33, fig. 1_. No traces of leaves, or fruit, in connexion with the stems, have been observed. The subjoined sketches (_Lign._ 33, and 34,) 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 in _Lign. 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.

_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. See _Archives du Muséum d'Histoire Naturelle_, tom. i. Paris, 1839.

_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 tissue
_d._ 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. (× ×.)
]

The annexed figure (_Lign. 35_) is an outline of the specimen, of the natural size; but this sketch is a mere plan or diagram, 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.

[Sidenote: SIGILLARLA ELEGANS.]

The external surface of this specimen possesses the characteristic markings of the insertion of the leaf-stalks of _Sigillaria 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 in _Plate V. fig. 7_.

The _inner_ circle of this zone, indicated by the _convex 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 in _Lign. 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.

[Sidenote: 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.

_Carboniferous. Derbyshire._--1/4 _nat._

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 at _a_; 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 in _Lign. 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.

(_M. Adolphe Brongniart._)

This specimen shows that the cylinder (_a_ in _Lign. 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 (see _Lign. 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, seen by a high power and transmitted light, is figured _Pl. V. fig. 6_; the smooth interspaces are composed of cellular tissue.

_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.
]

[Sidenote: 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 important discovery; 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.[CZ]

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

[Sidenote: 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.

Fig. 1.--A terminal Branch of a Lepidodendron; _nat._

2.--Leaf-scars on the stem of a Lepidodendron; _nat._

_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 of _Lepidodendra_, 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 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.[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 in _Lign. 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.

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 the _Lycopodiaceæ_, 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; most of 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 in _Wond._ 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 of _Lepidostrobi_ (scaly-cones), and are unquestionably the fruit of the trees with which they are imbedded.

[Sidenote: 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 in _Lign. 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 changes which 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.

_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 in _Lign. 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 Lepidostrobus jeune, 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 the _Ophioglosseæ_ and _Lycopodiaceæ_) is expressed by the name _Triplosporite_, 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 30_l._!

[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, _Lycopodites_ _Benettiæ_, is figured _Wond._ p. 723.

[Sidenote: 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 named _Calamities_ (ante, p. 107), and _Equisetites_ (_ante_, p. 106), are sufficiently distinct from the above to be easily recognized, I will briefly notice those not previously described.

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 in _fig. 1, Lign. 41_. These plants 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 as _Knorria taxina_, _Lign. 41, fig. 2_, closely resembles a young branch of Yew (_Taxus_), and perhaps might be more correctly named _Taxites_.

_Bothrodendron and Ulodendron._--These genera, together with _Megaphyton_, 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]

[115] Figured in Bd. pl. lvi.

In _Megaphyton_, the large ovate scars indicate the attachment of deciduous branches or gigantic leaves, which did not grow all round the stem, but in a regular order of superposition on each side.[116]

[116] Figured in Pict. Atlas, pl. xxv.

[Sidenote: ASTEROPHYLLITES.]

Asterophyllites.--I shall conclude this notice of some of the most characteristic trees of the Carboniferous Flora, with an account of a tribe of plants whose remains are so common in the coal-shales and grits, that there are but few large slabs with vegetable remains that do not exhibit examples of the elegant verticillate foliage of one or more species. The term _Asterophyllites_, (expressive of the star-like form of the leaves,) applied to this family by M. Ad. Brongniart, includes several fossil plants which are known to geologists under different generic names; the following concise account may be useful to the student.[117]

[117] Consult _Tableau des Genres de Végétaux Fossiles_, par M. Ad. Brongniart. Diet. d'Hist. Nat. Paris, 1849.

1. _Calamodendron._--These are arborescent stems, ligneous internally, and covered with a smooth carbonaceous crust, without regular longitudinal striæ, and not articulated; but the woody axis covered by this bark is deeply striated and articulated, resembling in this respect the true Calamites. These stems have a large central pith, or medullary column, surrounded by a ligneous zone, which is formed of radiated bands, without circles of growth: the structure of the carbonized bark is unknown.

2. _Asterophyllites._--These are supposed to be the branches and foliage of the stems above described.

3. _Sphenophyllum._--Plants, differing in the form of the leaves, but analogous in structure and mode of fructification to the Asterophyllites.

4. _Annularia._--Herbaceous aquatic plants, distinct from the preceding.

5. _Volkmannia._--These fossil plants are Asterophyllites in fructification.

The _Asterophyllites_ (_Lign. 42_) had branched articulated stems, with verticillate leaves, arranged perpendicularly to the branches which supported them: but as the foliage is in most instances partially concealed, the natural form is but seldom observable.

The original plants are supposed to have been a tribe of flowering dicotyledons, for small seed-vessels resembling those of the Cypress are often found with the foliage.

Asterophyllites equisetiformis; _nat._

_Coal-shale._ (_Foss. Flor._)]

[Sidenote: ANNULARIA CARDIOCARPON.]

The _Annulariæ_ were herbaceous plants with verticillate foliage like the former, but the whorls were arranged on the same plane with the stems on which they grew, and their remains have a very elegant appearance when expanded in the coal schists. It is supposed that they were aquatic plants, and that the stems and leaves floated on the surface of the water.[118]

[118] _Wond._ p. 717. Petrifactions, pp. 27, 43, &c. For coloured figures see Pictorial Atlas, pl. v.

Sphenophyllum (_wedge-shaped leaf_). _Lign. 43._--The fossil vegetables thus named, though somewhat resembling in their elegant verticillate foliage the Asterophyllites, differ essentially, and are regarded by M. Brongniart as herbaceous plants related to the _Marsiliaceæ_, or Pepper-worts. The leaves are triangular, truncated at the summit, and very deeply lobed and dentated. The fructification consists of sessile axillary or terminal spikes, composed of verticillate bracteæ, covering the receptacles. This mode of fructification resembles that of the Asterophyllites.[119]

[119] For details consult _Tab. des Genres de Vég. Foss._ p. 52.

Cardiocarpon.--_Lign. 44. fig. 1._--These are small fossil fruits or seed-vessels, which much resemble those of the Thuja or _Arbor-vitæ_, and are so often found imbedded with masses of the foliage of Asterophyllites, that it is conjectured they belong to those plants. They occur in groups of from five to twenty, and evidently were _didymous_, _i.e._ grew in pairs. _Fig. 1a_. is an enlarged view, to show the surface left by the attachment of the twin-seed.

Fig. 1.--Sphenophyllum Schlotheimii; _nat._
2.--Sphenophyllum erosum.

_Coal-Shale._]

Trigonocarpum. _Lign. 44. figs. 3. 4._--These fruits, which resemble those of certain Palms, are often met with in the coal-mines of Leicestershire and Yorkshire; frequently occurring in groups of thirty or forty, as if they were the scattered seeds of a raceme of a Palm: they are referred to the genus Nœggerathia, a tree of the carboniferous formation allied to the Palms.

[Sidenote: FOSSIL FRUITS.]

A figure of a fossil fruit from the Oolite--Carpolithes Bucklandi, is introduced in _Lign. 44, fig. 2_, and will be described hereafter.

Fig. 1.--Cardiocarpon acutum. _Snibstone Coal-mine, Leicestershire._

1_a_.--One of the above magnified.

2.--Carpolithes Bucklandii. _Coralline Oolite, Malton._

3.--Trigonocarpum olivæforme. _Snibstone Colliery._

4.--Trigonocarpum Nöggerathi.
]

The reader will observe that the fossil vegetables hitherto described belong, with but few exceptions, to the Carboniferous flora; and that the remains of Ferns, Calamites, Sigillariæ, and Lepidodendra, compose in a great measure those prodigious accumulations of mineral fuel, or coal, which supply the luxuries and necessities created by civilization.

Our review of fossil plants will now assume somewhat of a botanical arrangement, and we proceed to notice some of the most characteristic vegetable forms of the secondary and tertiary formations. We commence our examination with those remarkable tribes of gymnosperms, the Cycadaceæ, which comprise the Zamiæ and Cycadeæ.

Fossil Cycadaceæ.

The plants of this subdivision of the vegetable kingdom, from their singular structure and mode of growth, their simple cylindrical stems, and coronets of pinnated foliage, resembling that of certain palms, their usually gyrate vernation like that of the ferns, and their anomalous inflorescence and fructification, are objects of great interest to the scientific botanist; while the abundance of their fossil remains in the secondary formations renders them of the highest importance to the geologist.

Foliage and upper part of the Stem of Cycas revoluta 1/12 _nat._

_In Kew Conservatory._]

As many kinds of Zamia[120] and Cycas are cultivated in our hot-houses, the general appearance of the plants of this order must be familiar to the reader: the annexed figure of a beautiful living Cycas in the Royal Gardens at Kew, will serve to illustrate the general aspect of these exotics.

[120] The Linnæan genus Zamia is now separated into five or six genera, as Encephalartos, Macrozamia, Dion, &c.

The Zamiæ are short plants, with stout cylindrical stems, beset with thick scales, which are the bases of the petioles that have been shed: towards the summit the stem is garnished with a crown of elegant leaves; the fruit resembles the cones of pines. The leaves are pinnated, and very tough; their venation is either parallel as in endogens, or dichotomous as in ferns, but never reticulated as in exogens: in a young state they are coiled up like a crosier, as in ferns.

The Cycadeæ have the general aspect of the Zamiæ, but differ in their fructification and other characters; and some species have the stem bifurcated towards the top, and attain a height of upwards of twenty feet; for example, _C. circinalis_.

The stem in its internal structure[121] bears a close analogy to that of the Coniferæ; it has a central medullary column surrounded by a ligneous cylinder, divided by cellular medullary rays, each composed of bundles of vessels, and a thick cellular cortical investment or false-bark,[122] composed of the persistent scales that formed the bases of the petioles. (See _Pl. V. fig. 5._)

[121] See _Bd._ pl. lxii.

[122] See _Bd._ vol. i. pp. 494-498, for detailed description of structure in recent and fossil Zamiæ and Cycadeæ.

The existing species of Cycadaceæ are exclusively natives of hot regions, and chiefly inhabit the West Indies, South Africa, Equinoctial America, Japan, New Holland, &c.; not one species is known in Europe: a fact in striking contrast with the abundance of fossil plants of this order, which occur throughout the secondary formations of England and the continent.[123]

[123] The most interesting collection of living Cycadeæ and Zamiæ near London, is that of James Yates, Esq., of Lauderdale House, Highgate; it comprises choice examples of several of the sub-genera into which these plants are now divided by botanists.

No true cycads have hitherto been discovered in the carboniferous deposits; it is in the floras of the secondary epochs, from the new Red to the Cretaceous inclusive, that this tribe of plants forms an important feature. The foliage, stems, and fruits, occur in a fossil state; and as these organs cannot be referred with certainty to their respective plants, distinct genera are formed for their reception.

_Foliage._--From the tough and durable nature of the leaves, the foliage of the Cycadeæ occurs in a fine state of preservation; and in the fluvio-marine deposits of the Oolite of Yorkshire, many specimens of great beauty have been collected. I know not another locality in England so rich in fossils of this kind, as the cliffs along the coast near Scarborough; Gristhorpe Bay is well known to collectors. Not only the leaves, but also the fruits or cones occur, and of these, examples are to be seen in most public museums.[124] The leaves are carbonized, but the venation is well preserved.

[124] British Museum: see Petrifactions, p. 54, Room 1, Case F.

_Oolite, Scarborough._]

The leaflet of the recent Cycas is distinguished by a strong nervure, which runs along the middle; that of Zamia has no midrib, but fine parallel veins that pass direct to the margin.

Pterophyllum comptum. _Lign. 46._--The general aspect of these fossils is shown in this figure of a leaf, referred to the genus _Pterophyllum_, which is characterized by leaflets, often slightly united at their base, truncated at the summit, of a quadrangular or oblong form, and having fine, straight, parallel veins. The leaves are ten or twelve inches long, and have fine lanceolate leaflets; they are abundant in the same beds, and are often associated with the cones or fruit[125] figured in _Lign. 48_.

[125] Brit. Mus. Petrifactions, p. 55.

[Sidenote: ZAMITES PECTINATUS.]

Zamites pectinatus. _Lign. 47._--In the Stonesfield slate, collocated with remains of reptiles, fishes, insects, and mollusks, leaves and fruits of cycads are occasionally met with. A portion of a leaf nine inches long is here figured. The Lias of Dorsetshire has yielded many beautiful relics of this family[126]

[126] In the carboniferous strata of Eastern Virginia, United States, which are referred by Professor Rogers to the Oolitic epoch, leaves of Cycadeous plants are abundant. See Trans. American Geol p. 298.

_Oolite, Stonesfield._]

But few vestiges of the foliage of Cycads have been observed in the Wealden formation of England; one elegant leaf, however, of an undescribed species, was obtained some years since, from a sandstone quarry in Surrey, and is figured in my Geology of the South-east of England, p. 238; it is named in honour of my distinguished friend, M. Ad. Brongniart, _Cycadites Brongniarti_. The Wealden of the north of Germany is very rich in fossil Cycadeæ; my friend. Dr. Dunker, has figured and described twelve species in his admirable work on the organic remains of that formation.[127]

[127] Mon. Norddeutschen Weald, tab. i. to vii.

_Fruits._--The cones or fruits which occur with the foliage of Zamiæ in the carbonaceous shales and marls of the Oolite of the Yorkshire coast, are very fine, and have been described under the various names of _Zamites Mantelli_, _Z. gigas_, and _Z. lanceolatus_.

An interesting memoir on the structure of these fossils, by James Yates, Esq. (a gentleman distinguished for his knowledge of the recent Cycadaceæ), is published in the Proceedings of the Yorkshire Philosophical Society for 1849, p. 37; and another communication on the same subject by my friend Professor Williamson, of Manchester, in _York. Phil. Trans._ 1819, p. 45; to these papers I must refer for a detailed account of all that is at present known respecting their organization.

_From near Scarborough._

The surface of the cone is concealed by the bracteæ.]

Zamites Mantelli.[128] _Lign. 48._--The leaves associated with the fruit here figured, have lanceolate leaflets that insensibly contract at the base, and are inserted obliquely into the rachis; thus resembling the foliage of the recent _Encephalartos_. With these leaves, and the ovate cones (_Lign. 48_), are occasionally found a circle of leaves or elongated scales, locally termed "_collars_," which Professor Williamson has shown to be a zone formed by a scaly bud in which the germ of the plants was inclosed. In the progress of development, the fruit burst through the upper part of the investing sheath, and, as it grew to maturity, rose above the incurved elongated bracteæ, till the latter formed a zone or "collar" around the pedicle of the cone.[129] These fossils have been mistaken for flowers.[130]

[128] _Podozamites_ of Braun.

[129] Proc. Yorkshire Philos. Soc. 1849, p. 45.

[130] Bird's Yorkshire, tab. i. figs. 1 and 7.

It does not appear that the structure of the cone has been preserved in any of the specimens, so as to demonstrate the characters of the original; in all those I have examined, the surface of the fruit is concealed by the elongated bracteæ, which are pressed flat, and adhere so firmly to the inclosed body, as to render it impossible to ascertain its nature.[131] Mr. Williamson is of opinion that the plant resembled the recent _Cycas circinalis_, in its great height, and lax habits; and states, that he had seen portions of leaves that were three feet in length.

[131] Brit. Mus. Petrif. p. 55.

Zamites crassus. _Lign. 49, fig. 1._--In Sandown Bay, on the south coast of the Isle of Wight, where the Wealden beds rise to the surface from beneath the lowest strata of Greensand on the east and west, several cones have been found, associated with other vegetable remains, and bones of the Iguanodon, &c. A fossil cone from this locality is here figured; it bears considerable resemblance to the fruit of the recent _Encephalartos_.

[Sidenote: ZAMITES OVATUS.]

Zamites ovatus. _Lign. 49, fig. 2._--A few examples of cycadeous fruits have been collected from the Greensand of Kent and Sussex. The beautiful fossil represented, _Lign. 49, fig. 2_, from Foss. Flor. is referred to the Zamiæ, by the eminent authors of that work; but it presents in its imbricated character a greater analogy to a pine cone.

Fig. 1.--Zamites Crassus. _Wealden, Isle of Wight._

2.--Zamites Ovatus. _Greensand, Kent._
]

Zamites Sussexiensis.--At Willingdon, near Eastbourn, in Sussex, a cone nearly six inches long was discovered in a bed of Greensand, which abounds in fossil coniferous wood: it is of an elongated cylindrical form, and covered with hexagonal scales. I have provisionally named it _Zamites Sussexiensis_ (Geol. Proc. 1843), as it presents a nearer resemblance to the fruit of Zamiæ than to that of Conifers.

Trunks and Stems of Cycadaceæ.--In this section I shall notice the fossil plants which occur so abundantly in the fresh-water deposits that overlie the marine oolitic limestone of the Isle of Portland, and which must be familiar to my readers, from the graphic account of the circumstances under which they occur, by Mr. Webster, and subsequently by Dr. Buckland, and Sir H. De la Beche. In my Wonders of Geology, p. 387, and Geol. Isle of Wight, p. 395, the geological phenomena of that most interesting locality, the Isle of Portland, are so fully described, that it will not be necessary to dwell upon them; the structure and affinities of the fossil vegetables are the especial objects of our present inquiry.

[Sidenote: MANTELLIA NIDIFORMIS.]

(_Cycadites megalophyllus._ _Bd._)

_Wealden. Isle of Portland._

_a._ Central mass of cellular tissue, _b._ Circle of ligneous plates, _c._ Zone of cellular tissue, _d._ False-bark.]

Mantellia. _Lign. 50, 51._--The fossil Cycadeæ of the Isle of Portland were first described botanically by Dr. Buckland, (Geol. Trans, vol. ii. 2d Series,) under the name of _Cycadeoidea_; of which Memoir the account in _Bd._ p. 404, is an abstract. M. Ad. Brongniart, considering these plants as a peculiar type, referred them to a new genus, which he did me the honour to name _Mantellia_ (_Prod. Veg. Foss._). These stems or trunks are from one to two feet in height; the circumference of the largest not exceeding three feet. The stem is subcylindrical, and the external surface covered with the rhomboidal scars formed by the attachment of the leaf-stalks, and which are widest in their transverse diameter.

There are two species, which are readily distinguished by the form of the stems, and the difference in the size of the cicatrices left by the petioles.

The most common kind is short, and spheroidal, and the leaf-scars are relatively large; its shape has caused it to be named "_Crows' nest_," by the quarrymen, who believe these plants to be nests that were built by crows in the trees of the petrified forest with which they are imbedded. The specific name (_nidiformis_) adopted by M. Brongniart, expresses this popular notion.

_Lign. 50._ represents a fine example from the Portland Dirt-bed, which exhibits a structure altogether similar to that which characterizes the stems of recent cycadeous plants; namely, (_a_) a central mass of cellular tissue surrounded by circles of laminated ligneous rays or plates (_b_); then a zone of cellular tissue (_c_), and an external cylinder of false-bark (_d_). The mode of increase by buds, from germs in the axillæ of the petioles, as in the living plants, is also distinctly seen.

(_Brongn._); 1/8 _nat._

(_Cycadites microphyllus. Bd._)

_Wealden. Petrified Forest of the Isle of Portland._]

The other species is subcylindrical, and the leaf-scars are much smaller and more regular than in _M. nidiformis_, indicating a more delicate foliage, as expressed by Buckland's specific name: that of M. Brongniart refers to the cylindrical form of the stem. This plant was higher and more slender than its associate. Numerous buds are seen in the axillæ of the petioles in the specimen figured.

These fossils present, both externally and internally, a close relation to the bulbiform stems of the recent Cycadeæ, named _Encephalartos_, of South Africa.[132]

[132] The fossil Cycads of the Isle of Portland are admirably described and illustrated in Dr. Buckland's Bridgewater Essay, (p. 497, and pl. lx. lxi.), and their internal structure is fully explained.

Neither the leaves nor the fruit are known: a cone found in the Dirt-bed of Portland, and attributed to these plants, appears to belong to the coniferæ of the petrified forest. Examples of Mantelliæ have been found in the quarry of Portland-stone at Swindon, Wilts.

[Sidenote: CLATHRARIA LYELLII.]

_Wealden._

A branched example of the inner axis: the original 3-1/2 feet high.]

Clathraria[133] Lyellii. _Lign. 52-57._--The fossil plants to which I would next direct attention were first discovered by me in the Wealden strata of Sussex, in 1820, and were figured and described under the name they still bear, in my Fossils of Tilgate Forest, in 1827. The specimens figured in that work are the most illustrative hitherto discovered, with but one exception.[134]

[133] EC C lathraria, _i.e._ _lattice stem_, from the scars left by the petioles.

[134] They are now in the British Museum; see Petrifactions, p. 45. _Room_ I. _Case_ E.

From the imperfect state of the remains of these plants, the structure and affinities of the originals were very ambiguous, and the fossils have been placed by some eminent botanists with the Liliaceæ, and by others with the Asphodeleæ; their true botanical position is doubtless with the Cycadaceæ; for in some points they resemble the Zamiæ, in others the Cycadeæ.

The stem of the Clathraria is composed of a solid internal axis, the surface of which is covered with reticulated fibres; the large branched specimen of this part, figured in _Lign. 52_, is the finest example hitherto obtained: it was discovered, with bones of the Iguanodon, in a quarry near Cuckfield, Sussex, in 1820. The axis is invested with a very thick false-bark, formed of the consolidated bases of the leaf-stalks, the insertions of which are rhomboidal and transverse. The outer surface of the bark is consequently marked with elevated lozenge-shaped cicatrices (_Lign. 53_), separated from each other by a marginal furrow, which is surrounded by a parallel ridge or band of a fibrous structure.

1/4 _nat._

A stem, with rhomboidal transverse scars, left by the petioles; broken transversely and separated, to show the internal axis at _a_, which, if the pieces were united, would be received in the cavity below the depression, or cicatrix, on the middle of the upper portion, _b_, was probably the situation of a resinous secretion, like the dragon-blood in the Dracæna.]

The cortical zone is generally converted into a cylinder of stone, which in some examples separates from the axis. In a beautiful specimen of this kind, _Lign. 54_, the axis projects and is surrounded by the false-bark.

The axis is solid, and has its surface strongly marked with interrupted ridges. This surface has generally patches of vascular tissue adhering to it; and there are here and there deep pits, or lacunæ, which probably contained a resinous secretion. Thin transverse sections of the axis, prepared with Canada balsam, and examined under the microscope, only give faint traces of cellular tissue.

Clathraria Lyellii; 1/4 _nat._

_Wealden Sandstone._

_Tilgate Forest._

Portion of a stem, scored by the cicatrices of the petioles; showing the Axis _a_, surrounded by the cortical cylinder.]

I have spared neither trouble nor expense in endeavouring to detect the organization of this plant; numerous sections of stems have been cut, and examined microscopically, but very few exhibit any traces of structure; and in those which retain some vestiges of organization, the siliceous mass which permeates the vascular tissue, is not sufficiently transparent to yield satisfactory results. It can only be inferred that in their internal organization, as in their external characters, the Clathrariæ were most nearly allied to the Cycadeæ or Zamiæ. A remarkable specimen, (_Lign. 56_,) discovered in a stratum of Chalk-marl, near Bonchurch, confirms this view, and throws much light on the nature and relations of these vegetables.

Petiole of Clathraria Lyellii;

_a._ External aspect.

_b._ Inner surface.

_c._ Vascular pits left by the separation of the leaf.
]

This fossil is a portion of the summit of a stem garnished with persistent petioles, or leaf-stalks; it is fifteen inches in length, and nearly perfect at the top; and at the lower end, which has been broken off transversely, the inner axis (_Lign. 56 a_.), surrounded by the false-bark formed by the confluence and consolidation of the bases of the petioles, is exposed. The stem has been stript of the leaf-stalks at the lowermost part, and exhibits the characteristic lattice-like scars. The petioles are for the most part entire; some of them are abortive, and others, which have supported leaves, are marked on the summits with vascular pits, indicating that the foliage was shed naturally; as shown in _Lign. 55 a_. These petioles were probably persistent for some years, as in the existing Cycads. The opposite side of the stem to that represented is covered with elongated and flattened petioles.

Clathraria Lyellii; 1/4 _nat._

_Chalk-marl. Bonchurch, Isle of Wight._

The summit of a stem garnished with petioles; the lower part shows the cicatrices left by the removal of some of the petioles: _a_, the internal axis.]