sub-cylindrical block of sandstone, very smooth, and marked externally with small crescent-shaped spots, which are the terminations of bundles of vascular tissue.

A transverse section of this fossil proved it to be a portion of the stem of the Endogenites erosa, in a better state of preservation than any example previously obtained. The openings, instead of being empty, are for the most part occupied by the vessels; and an external band, or zone, of vascular tissue, disposed somewhat in festoons, is tolerably well preserved. Very thin slices, immersed in Canada balsam, to render them as transparent as the dull siliceous substance of which they are composed will admit of, examined under the microscope, indicate, in the opinion of Dr. Robert Brown, a nearer approach to the cycadeæ than to the endogenous tribes.

FOSSIL CYCADEOUS PLANTS.-Among the coniferæ, or cone-bearing plants, the Cycadea and Zamia are remarkably distinguished by the peculiarity of their fructification, their seeds being exposed; hence the name of the order in which these plants are arranged-gymnospermous, i.e., naked seeds. The organisation of their stems is also different from that of the other coniferæ.* As several species of zamia and cycas are cultivated in our greenhouses, their general aspect, which approaches that of the palms, must be familiar to the reader. Most of the zamiæ are short plants, with stout cylindrical stems, beset with thick scales, which are the petioles, or leaf stalks, left after the leaves have fallen off. On the summit of the stem is a crown of elegant pinnated leaves, with simple veins. The fruit bears some resemblance to the cones of the pines, but the seeds are not enclosed in receptacles. The cycadeæ resemble the zamiæ, but the trunk is in general longer; one species, Cycas circinnalis, attains a height of thirty feet. The stem is in most species simple, but in some it is dichotomous,

* See Dr. Buckland's "Bridgwater Essay," p. 490..

FOSSIL CYCADEOUS PLANTS.

213

dividing into two or more branches; the leaves are tough, and in the young state coiled up like a crosier, as in the ferns. These plants are inhabitants of hot and humid climates, and abound in the West Indies, Molucca Isles, &c. A few plants of this order have been detected in the carboniferous strata; and in the lias and oolite they appear in immense numbers; several species have been found in the Wealden and cretaceous formations. The discovery of cones of a species of zamia (Z. crassa, “Medals of Creation," p. 160), associated with bones of the iguanodon, in the Wealden strata in Sandown Bay, has already been mentioned (p. 99).

CLATHRARIA LYELLII.-But the most interesting fossil plant belonging to this tribe of coniferæ, of which any remains have been found in the Wealden, is that discovered by me in Sussex, and described in 1822; and subsequently in "The Fossils of Tilgate Forest," under the name of Clathraria Lyellii.*

This plant was formerly classed with the Liliaceae, by that eminent botanist M. Adolphe Brongniart; but the discovery of more illustrative specimens than those first obtained, indicate its affinity to the cycades, with which M. Brongniart has some years since arranged it. The stem of the clathrariat is composed of an axis having the surface covered with reticulated fibres, and of a false bark produced by the union of the consolidated bases of the petioles, the insertions of which are rhomboidal and transverse. The external surface of the stem is in consequence covered with lozenge-shaped elevated scars, separated by lateral depressions, which are surrounded by a parallel band of a fibrous appearance (see lign. 22). This outer portion is sometimes

* "Fossils of Tilgate Forest," Plates I. II. III., and "Geology of the South-East of England," Pl. I.

+ Clathraria, or latticed stem; so named from the scorings left on the stem by the attachment of the petioles.

consolidated into a compact cylinder of stone, which will separate from the central axis ("Fossils of Tilgate Forest," PI. II.): the latter is solid, and strongly marked externally

with reticulated interrupted ridges. This surface has generally patches of vascular tissue adhering to it, but these are in so friable a condition, that microscopical examination has thrown no light upon their structure.* On some parts of the internal axis there are deep pits, indicating the lacunæ in which a resinous secretion was contained.

The waterworn portion of a stem, figured in lign. 22, which I picked up on the sea-beach in Brook Bay, is the only specimen of the Clathraria I have seen from the Wealden of the Isle of Wight. This fragment is highly interesting, for the calcareo-siliceous earth, of which the stem now consists, is of a finer texture than in any of the Tilgate Forest specimens, and transverse sections display under

For other details I must refer to the "Medals of Creation," vol. i. p. 182. All the specimens figured in my previous works are in the British Musuem, in the room appropriated to fossil vegetables.

CLATHRARIA LYELII.

215

the microscope, more satisfactory indications of the organisation of the original. Without many figures, and more lengthened descriptions than our space will admit of, the peculiarities of structure exhibited in these slices could not be demonstrated; it must therefore suffice to state, that the organisation, so far as it can be determined, shows a near approach to that of the cycadeæ.

But additional and most important information as to the external form of the clathraria, has been afforded by the splendid specimen from the chalk marl of the Undercliff, mentioned in a previous chapter (Chap. VIII. p. 178), as having been discovered by Captain Ibbetson, and now exhibited in his collection of Isle of Wight fossils, in the Polytechnic Institution. This invaluable relic is admirably represented by Mr. Dinkel,* and engraved by Mr. Lee, in lign. 23, p. 217.

The

This specimen consists of the summit of the stem, and is fifteen inches in length; the appearance of the lower end shows that some portion has been broken off and lost. stem is compressed into an elliptical form; the figure exhibits the longest diameter, and the side on which the characters of the plant are best preserved. On the upper 10 inches, this trunk is covered by the petioles or leafstalks; and these appendages remain on one side almost to the lower extremity. The surface of the inferior portion, to the extent of four inches, is marked with transverse lozenge-shaped scars, produced by the separation of the petioles; the internal axis appears at the fractured end: see lign. 23, a. The leaf-stalks are from one to two inches

*This eminent artist now permanently resides in London, being engaged at the British Museum by Dr. Falconer, on the illustrations for the important work on the sub-Himalayan Fossils, which is now in progress of publication. For subjects requiring talent, accuracy, and knowledge of animal and vegetable organisation, for their successful delineation, the pencil of Mr. Dinkel will be found invaluable.

N

wide, rounded above, and contracted below, as shown in the detached petiole figured in lign. 24; they are traversed. by fine and nearly parallel longitudinal veins.

The

a

LIGN. 24.-A PETIOLE OF CLATHRARIA LYELLII, SEPARATED FROM THE STEM.

a, the external aspect;

b, the internal surface;

c, the vascular markings left on the summit of the petiole by the
separation of the leaf.

summits of those petioles from which the leaves appear to have been shed, not broken off, are marked by vascular pits disposed with great regularity, as shown at c, lign. 24; a structure which M. Adolphe Brongniart informs me partakes more of the character of the Ferns, than of the cycadeæ. The substance of this fossil is a sandy marl, and probably does not retain any traces of the internal structure of the original; still it is desirable that sections of the petioles and of the stem should be microscopically examined. M. Adolphe Brongniart, to whom I transmitted a sketch of this specimen of the natural size, immediately favoured me with his remarks on this interesting fossil. He considers the specimen to be the upper termination of a stem of the clathraria, garnished with persistent leaf-stalks; and that some of the uppermost petioles were broken off accidentally while the leaves were alive; but that in the lower ones, which possess vascular markings on their summits, the leaves were detached naturally, and these petioles remained, probably for some years, as is the case in the existing cycadeæ. The petioles having fallen from the exposed part of the stem, the surface is left bare, and is