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trunk and scales, in our search for their distinguishing characters.
, 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 Cycadeae.f
* 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 Gycadites 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.
t 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 AxilleB of the leaf stalks.
The section given in PI. 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; (PI. 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, PI. 60, Fig. 1, A. B. C. D.
The Cycadites microphyllus, PI. 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 cirde 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
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, (PI. 59, Fig. 3.) This sectionwas 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 Cycadeae; and is figured in Geol. Trans. N. S. vol. ii. PI. 46.
* In PI. 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 PI. 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 PI. 62, Fig. 3, c'.
A similar arrangement of nearly all these parts exists in the transverse section of the leaf stalks of recent Cycadece. In Cycas circinalis, and C. revoluta, and Zamia furfuracca, 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 PI. 62, Fig. A shows the place of these bundles of vessels in a transverse section of the leaf stalk of Za mi a 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 Cycadeee 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 PI. 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 Cycadeffi. PI. 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 Cycadece.
The Cycas revoluta figured in PI. 58* possesses a peculiar interest in relation to both our fossil species, in consequence of its protruding a series of buds from the axillae of many of the scales around its trunk. These buds explain analogous appearances at the axillae of many fossil scales on Cycadites megalophyllus, and Cycadites microphyllus (see PI. 60, Fig. 1, and PI. 61, Fig. 1,) and form an important point of agreement in the Physiology of the living and fossil Cycadeae*
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, impervious to air and moisture.
A similar disposition is seen in the longitudinal section of the fossil Petiole of Cycadites microphyllus represented at PI. 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 Cycadese; 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 Cycadeffi and Coniferae, such as have been described in speaking of fossil Conifers, 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 Za. mia 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 drupoe, in Earl Fitzwilliam's hothouse at Wentworth, threw out a number of buds, from the axillffi of the leaf-scales soon after the Cone was cut off from its summit. Jin Linn. Transvol. vj. 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,
Thus, we see that our fossil Cycadites are closely allied by many remarkable characters of structure, to existing Cycadeae.
1. By the internal structure of the trunk, containing a radiating circle, or circles, of woody fibre, embedded in cellular tissue. 2. By the structure of their outer case, composed of persistent bases of petioles, in place of a bark; and by all the minute details in the internal organization of each Petiole. 3. By their mode of increase by Buds protruded from germs in the Axillae of the Petioles.
* In the fossil trunk of Cycadites microphyllus, PI. 61. Fig. 1, we see fourteen Buds protruding from the axillee of the leaf stalks, and in PI. 60, Fig. 1, we have three Buds in a similar position in Cycadites megalophyllus.
In PI. 61, Figs. 2, 3, exhibit transverse sections of three Buds of Cycadites mycrophyllus. The section of the uppermost bud, Fig. 3, g, passes only through the leaf stalks near its crown. The section of the bud. Fig. 3, 'd, being lower down in the embryo trunk, exhibits a double woody circle, arranged in radiating plates, resembling the double woody circle in the mature trunk, PI. 61,1, B,b. But in PI. 61, Fig. 2, the laminated circle within the embryo trunk near d, is less distinctly double, as might be expected in so young a state.
At PI. 62, Fig. 3, d, and d', we see magnified representations of a portion of the embryo circle within the Bud, PI. 61. Fig. 3, 'd. These woody circles within the buds, are placed hetween an exterior circle-of cellular tissue' interspersed with gum vessels, and a central mass of the same tissue, as in the mature stems.
On the right of the lower bud, PI. 61, Fig. 3, above b, and in the magnified representations of the same at PI. 62, Fig. 3, e, we have portions of a. small imperfect laminated circle. Similar imperfect circles occur also near the margin of the sections, PI. 61, Figs. 2. 3, at e% e', e"; these may be imperfectly developed Buds, crowded like the small Buds near the base of the living Cycas, PI. 58: or they may have resulted from the confluence of the bundles of vessels, in the Bases of leaves, forced together by pressure, connected with a diminution or decay of their cellular substance. The normal position of these bundles of vessels is seen magnified in PI. 62. Fig. 3. c. and in nearly all the Sections of Bases of petioles in PI. 61. Fig. 2,
However remote may have been the time when these Prototypes of the family of Cycadeee ceased to exist, the fact of their containing so many combinations of peculiarities identical with those of existing Cycadeae, connects these ancient arrangements in the Physiology of fossil Botany, with those which now characterize one of the most remarkable families among existing plants. In virtue of these peculiar structures, the living Cycadeae form an important link, which no other Tribe of plants supplies, connecting the great family of Coniferae, with the families of Palms and Ferns, and thus fill up a blank, which would otherwise have separated these three great natural divisions of dicotyledonous, monocotyledonous, and acotyledonous plants.
The full development of this link in the Secondary periods of Geological history, affords an important evidence of the Uniformity of Design which now pervades, and ever has pervaded, all the laws of vegetable life.
Facts like these are inestimably precious to the Natural Theologian; for they identify, as it were the Artificer, by details of manipulation throughout his work. They appeal to the Physiologist, in language more commanding than human Eloquence; the voice of very stocks and stones, that have been buried for countless ages in the deep recesses of the earth, proclaiming the universal agency of One all-directing, all-sustaining Creator, in whose Will and Power, these harmonious systems originated, and by whose Universal Providence, they are, and have at all times been maintained.
The Pandaneae, or Screw-Pines, form a monocotyledonous family which now grows only in the warmer zones, and chiefly within the influence of the sea; they abound in the Indian Archipelago, and the islands of the Pacific Ocean. Their aspect is that of gigantic Pine apple plants having arborescent stems, (See PI. 63, Fig. 1,)