the recognition of similar structures in fossil plants, referable to a family whose characters are so remarkable.

The figure of a Cycas revoluta (Pl. 58,*) represents the form and habit of plants belonging to this beautiful genus. In the magnificent crown of graceful foliage surrounding the summit of a simple cylindrical trunk, it resembles a Palm. The trunk in the genus Cycas, is usually long. That of C. circinalis rises to 30 feet. In the genus Zamia it is commonly short.

Our figure of a Zamia pungens,‡ (Pl. 59,) shows the mode of inflorescence in this Genus, by a single cone, rising like a Pine Apple, deprived of its foliaceous top, from within the crown of leaves at the summit of the stem.

The trunk of the Cycadea has no true bark, but is surrounded by a dense case, composed of persistent scales which have formed the basis of fallen leaves; these, together with other abortive scales, constitute a compact covering that supplies the place of bark. (See Pl. 58 and 59.)

In the Geol. Trans. of London (vol. iv. part 1. New Series) I have published, in conjunction with Mr. De la Beche, an account of the circumstances under which silicified fossil trunks of Cycadeæ are found in the Isle of Portland, immediately above the surface of the Portland stone, and below the Purbeck stone. They are lodged in the same beds of black mould in which they grew, and are accompanied by prostrate trunks of large coniferous trees, converted to flint, and by stumps of these trees standing erect with their roots still fixed in their native soil. Pl. 57, Fig. 1.§)

(See

* Drawn from a Plant in Lord Grenville's Conservatory at Dropmore, in 1832.

↑ In Curtis's Botanical Magazine, 1828, Pl. 2826, Dr. Hooker has published an Engraving of a Cycas circinalis which in 1827 flowered in the Botanic Garden at Edinburgh. See Pl. 1. Fig. 33.

Copied from an engraving published by Mr. Lambert, of a plant that bore fruit at Walton on Thames in the conservatory of Lady Tankerville,

§ The sketch, Pl. 57, Fig. 2, represents a triple series of circular undula.

Pl. 57, Fig. 3, exhibits similar stumps of trees rooted in their native mould, in the Cliff immediately east of Lulworth Cove. Here the strata have been elevated nearly to a angle of 45°, and the stumps still retain the unnatural inclination into which they have been thrown by this elevation.

The facts represented in these three last figures are fully described and explained in the paper above referred to; they prove that plants belonging to a family that is now confined to the warmer regions of the earth, were at a former period, natives of the southern coast of England.*

As no leaves have yet been found with the fossil Cycadeæ under consideration, we are limited to the structure of their

tions, marked in the stone, which surrounds a single stump, rooted in the dirt-bed in the Isle of Portland. This very curious disposition has apparently resulted from undulations, produced by winds, blowing at different times in different directions on the surface of the shallow fresh-water, from the sediments of which the matter of this stratum was supplied, while the top of this stem stood above the surface of the water. See Geol. Trans. Lond. N. S. vol. iv. p. 17.

* The structure of this district affords also a good example of the proofs which Geology discloses, of alternate elevations and submersions of the strata, sometimes gradually, and sometimes violently, during the formation of the crust of our planet.

First. We have evidence of the rise of the Portland stone, till it reached the surface of the sea wherein it was formed.

Secondly. This surface became for a time, dry land, covered by a temporary forest, during an interval which is indicated by the thickness of a bed of black mould, called the Dirt-bed, and by the rings of annual growth in large petrified trunks of prostrate trees, whose roots had grown in this mould.

Thirdly. We find this forest to have been gradually submerged, first beneath the waters of a fresh-water lake, next of an estuary, and afterwards beneath those of a deep sea, in which Cretaceous and Tertiary strata were deposited, more than 2000 feet in thickness.

Fourthly. The whole of these strata have been elevated by subterranean violence, into their actual position in the hills of Dorsetshire.

We arrive at similar conclusions, as to the alternate elevation and depressions of the surface of the earth, from the erect position of the stems of Calamites, in sand-stone of the lower Oolite formation on the eastern coast of Yorkshire. (See Murchison. Proceedings of Geol. Society of London, vol. i. p. 391.)

trunk and scales, in our search for their distinguishing cha

racters.

I have elsewhere (Geol. Trans. London, N. S. vol. ii. part iii. 1828) instituted a comparison between the internal structure of two species of these fossil trunks, and that of the trunks of a recent Zamia and recent Cycas.*

I must refer to the memoir, in which these sections are described, for specific details as to the varied proportions and numerical distribution of these concentric circles of laminated wood and cellular tissue, in the trunks of living and fossil species of Cycadeæ.

*M. Ad. Brongniart has referred these two fossil species to a new genus, by the name of Mantellia nidiformis and Mantellia cylindrica; in my paper just quoted, I applied to them the provisional name of Cycadeoidea megalophylla and Cydadeoidea microphylla; but Mr. Brown is of opinion, that until sufficient reasons are assigned for separating them from the genus Cycas or Zamia, the provisional name of Cycadites is more appropriate, as expressing the present state of our knowledge upon this subject. The name Mantellia is already applied by Parkinson (Introduction to Fossil Org. Rem. p. 53) to a genus of Zoophytes, which is figured in Goldfuss, T. vi. p. 14.

Plates 60, Fig. 1, and 61, Fig. 1, represent very perfect specimens of fossil Cycadites from Portland, now in the Oxford Museum; both having the important character of Buds protruding from the Axille of the leaf stalks.

The section given in Pl. 59, Fig. 2, of the trunk of a recent Zamia horrida, from the Cape of Good Hope, displays a structure similar to that in the section of the fossil Cycadites megalophyllus from the Isle of Portland; (Pl. 60, Fig. 2) each presents a single circle of radiating lamina of woody fibre, B, placed between a central mass of cellular tissue, A, and an exterior circle of the same tissue, C. Around the trunk, thus constituted of three parts, is placed a case or false bark, D, composed of the persistent bases of fallen leaves, and of abortive scales. The continuation of the same structure is seen at the summit of the stem, Pl. 60, Fig. 1, A. B. C. D. The Cycadites microphyllus, Pl. 61, Fig. 1, affords a similar approach to the internal structure of the stem in the recent Cycas. The summit of this fossil exhibits a central mass of cellular tissue (A,) surrounded by two circles of radiating woody plates, B. b., between these laminated circles, is a narrow circle of cellular tissue, whilst a broader circle of similar cellular tissue (C) is placed between the exterior laminated circle, (b) and the leaf scales (D.) This alternation of radiating circles of wood VOL. I.-32

374

STRUCTURE OF SCALES OR BASES OF LEAF STALKS.

A strict correspondence is also exhibited in the internal structure of the scales, or bases of leaf stalks surrounding the trunks of our fossil Cycadites, with that of the corresponding scales in the recent species.*

with circles of cellular tissue, is similar to the two laminated circles near the base of a young stem of Cycas revoluta, (Pl. 59, Fig. 3.) This section was communicated to me by Mr. Brown early in 1828, to confirm the analogy which had been suggested from the external surface, between these fossils, and the recent Cycadex; and is figured in Geol. Trans. N. S. vol. ii. Pl. 46.

* In Pl. 61, Figs. 2, 3, represent two vertical sections of a Cycadites microphyllus from Portland, converted to Calcedony. These slices are parallel to the axis of the trunk, and intersect transversely the persistent bases of the Petioles or Leaf stalks. In each rhomboidal Petiole, we see the remains of three systems of vegetable structure, of which magnified representations are given Pl. 62, Fig. 1, 2, 3. We have, first, the principal mass of cellular tissue (f;) secondly, sections of gum vessels (h) irregularly dispersed through this cellular tissue; thirdly, bundles of vessels, (c,) placed in a somewhat rhomboidal form, parallel to, and a little within, the integument of each petiole. These bundles of vessels are composed of vascular woody fibres proceeding from the trunk of the plant towards the leaf. See magnified section of one bundle at Pl. 62, Fig. 3, c'.

A similar arrangement of nearly all these parts exists in the transverse section of the leaf stalks of recent Cycades. In Cycas circinalis, and C. revoluta, and Zamia furfuracea, the bundles of vessels are placed as in our fossil, nearly parallel to the integument. In Zamia spiralis, and Z. horrida, their disposition within the Petiole, is less regular, but the internal structure of each bundle is nearly the same. In Pl. 62, Fig. A shows the place of these bundles of vessels in a transverse section of the leaf stalk of Zamia spiralis; Fig. A. c'. is the magnified appearance of one of the bundles in this section; Fig. B, c" is the magnified transverse section of a similar bundle of vessels in the petiole of Zamia horrida. In this species the vasculur fibres are smaller and more numerous than in Z. spiralis, and the opake lines less distinct. Both in recent and fossil Cycades the component vascular fibres of these bundles are in rows approximated so closely to each other, that their compressed edges give an appearance of opake lines between the rows of vascular fibres, (see Pl. 62, Fig. 1, c'. Fig. B, c' and Fig. 3, c'.) These bundles of vessels seem to partake of the laminated disposition of the woody circular within the trunk.

An agreement is found also in the longitudinal sections of the Petioles of recent and fossil Cycadem. Pl. 62, Fig. 1, is the longitudinal section of part of the base of a Petiole of Zamia spiralis, magnified to twice the natural size. It is made up of cellular tissue, (f) interspersed with gum vessels, and with long bundles of vascular fibres, (c) proceeding from the

Mode of increase by Buds the same in recent and fossil Cycadea.

The Cycas revoluta figured in Pl. 58* possesses a peculiar interest in relation to both our fossil species, in consequence of its protruding a series of buds from the axilla of many of the scales around its trunk. These buds explain analogous appearances at the axilla of many fossil scales on Cycadites

trunk towards the leaf. On the lower integument, (b') is a dense coating of minute curling filaments of down or cotton, (a) which being repeated on each scale, renders the congeries of scales surrounding the trunk, impervi ous to air and moisture.

A similar disposition is seen in the longitudinal section of the fossil Petiole of Cycadites microphyllus represented at Pl. 62, Fig. 2, and magnified four times. At f, we have cellular tissue interspersed with gum vessels, h. Beneath c, are longitudinal bundles of vessels; at be, is the integument; at a, a most beautiful petrifaction of the curling filaments of down or cotton, proceeding from the surface of this integument.

In the vascular bundles within the fossil Petioles, (c) Mr. Brown has recognised the presence of spiral, or scalariform vessels (Vasa scalariforma) such as are found in the Petioles of recent Cycades; he has also detected similar vessels, in the laminated circle within the trunk of the fossil Buds next to be described. The existence of vessels with discs peculiar to recent Cycades and Coniferæ, such as have been described in speaking of fossil Coniferæ, has not yet been ascertained.

* This plant has been living many years, in Lord Grenville's conservatory at Dropmore. In the autumn of 1827, the external part of the scales was cut away to get rid of insects: in the following spring the buds began to protrude. Similar buds appeared also in the same conservatory on a plant of the Zamia spiralis from New Holland. In vol. vi. p. 501, Horticult. Trans. leaves are stated to have protruded from the scales of a decayed trunk of Zamia horrida in a conservatory at Petersburgh.

I learn from Professor Henslow, that the trunk of a Cycas revoluta, which in 1830 produced a cone loaded with ripe drupæ, in Earl Fitzwilliam's hothouse at Wentworth, threw out a number of buds, from the axilla of the leaf-scales soon after the Cone was cut off from its summit. In Linn. Trans. vol. vi. tab. 29, is a figure of a similar cone which bore fruit at Farnham Castle, 1799.

It is stated in Miller's Gardener's Dictionary, that the Cycas-revoluta was introduced into England about 1758, by Captain Hutchinson; his ship was attacked, and the head of the plant shot off, but the stem being preserved, threw out several new heads, which were taken off, and produced as many plants,