Imágenes de página
PDF
ePub

megalophyllus, and Cycadites microphyllus (see Pl. 60, F 1, and Pl. 61, Fig. 1,) and form an important point of agr ment in the Physiology of the living and fossil Cycadea

Thus, we see that our fossil Cycadites are closely all by many remarkable characters of structure, to exist Cycades.

1. By the internal structure of the trunk, containing a diating circle, or circles, of woody fibre, embedded in ce lar tissue. 2. By the structure of their outer case, compo of persistent bases of petioles, in place of a bark; and by the minute details in the internal organization of each tiole. 3. By their mode of increase by Buds protru from germs in the Axilla of the Petioles.

* In the fossil trunk of Cycadites microphyllus, Pl. 61. Fig. 1, we fourteen Buds protruding from the axilla of the leaf stalks, and in Pl. Fig. 1, we have three Buds in a similar position in Cycadites megalophyl

In Pl. 61, Figs. 2, 3, exhibit transverse sections of three Buds of C dites mycrophyllus. The section of the uppermost bud, Fig. 3, g, pa only through the leaf stalks near its crown. The section of the bud, 3, 'd, being lower down in the embryo trunk, exhibits a double woody cle, arranged in radiating plates, resembling the double woody circle in mature trunk, Pl. 61, 1, B, b. But in Pl. 61, Fig. 2, the laminated circle wi the embryo trunk near d, is less distinctly double, as might be expected i young a state.

At Pl. 62, Fig. 3, d, and d', we see magnified representations of a po of the embryo circle within the Bud, Pl. 61. Fig. 3, 'd. These woody cles within the buds, are placed hetween an exterior circle of cellular ti interspersed with gum vessels, and a central mass of the same tissue, the mature stems.

On the right of the lower bud, Pl. 61, Fig. 3, above b, and in the m fied representations of the same at Pl. 62, Fig. 3, e, we have portions small imperfect laminated circle. Similar imperfect circles occur also the margin of the sections, Pl. 61, Figs. 2, 3, at e, e', e"; these may be perfectly developed Buds, crowded like the small Buds near the base of living Cycas, Pl. 58: or they may have resulted from the confluence of bundles of vessels, in the Bases of leaves, forced together by pressure, nected with a diminution or decay of their cellular substance. The no position of these bundles of vessels is seen magnified in Pl. 62. Fig. 3. c in nearly all the Sections of Bases of petioles in Pl. 61. Fig. 2.

However remote may have been the time when these Prototypes of the family of Cycadeæ ceased to exist, the fact of their containing so many combinations of peculiarities identical with those of existing Cycadeæ, 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 Cycadeæ form an important link, which no other Tribe of plants supplies, connecting the great family of Coniferæ, 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.

Fossil Pandaneæ.

The Pandanes, 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 ar borescent stems. (See Pl. 63, Fig. 1.)

This family of Plants seems destined, like the Cocoa nut Palm, to be among the first vegetable Colonists of new lands just emerging from the ocean; they are found together almost universally by navigators on the rising Coral islands of tropical seas. We have just been considering the history of the fossil stems of Cycades in the Isle of Portland, from which we learn that Plants of that now extra-European family were natives of Britain, during the period of the Oolite formation. The unique and beautiful fossil fruit represented in our figures (Plate 63, Figs. 2, 3, 4,) affords probable evidence of the existence of another tropical family nearly allied to the Pandaneæ at the commencement of the great Oolitic series in the Secondary formations.*

In structure this fossil Fruit approaches nearer to Pandanus than to any other living plant, and viewing the peculiarities of the fruit of Pandaneæ,† in connexion with the office

* This fossil was found by the late Mr. Page, of Bishport near Bristol, in the lower region of the Inferior Oolite formation on the E. of Charmouth, Dorset, and is now in the Oxford Museum. The size of this Fruit is that of a large orange, its surface is occupied by a stellated covering or Epicarpium, composed of hexagonal Tubercles, forming the summits of cells, which occupy the entire circumference of the fruit. (Figs. 2, a. 3, a. 4, a. 8, a.)

Within each cell is contained a single seed, resembling a small grain of Rice more or less compressed, and usually hexagonal, Figs. 5, 6, 7, 8, 10. Where the Epicarpium is removed, the points of the seeds are seen, thickly studded over the surface of the fruit, (Fig. 2, 3, e.) The Bases of the cells (Fig. 3 and 10 c.) are separated from the receptacle, by a congeries of footstalks (d) formed of a dense mass of fibres, resembling the fibres beneath the base of the seeds of the modern Pandanus (Fig. 13, 14, 15, d.) As this position of the seeds upon foot-stalks composed of long rigid fibres, at a distance from the receptacle, is a character that exists in no other family than the Pandanex, we are hereby enabled to connect our fossil fruit with this remarkable tribe of plants, as a new genus, Podocarya. I owe the suggestion of this name, and much of my information on this subject, to the kindness of my friend, Mr. Robert Brown.

1

The large spherical fruit of Pandanus, hanging on its parent tree is represented at Pl. 63, Fig. 1. Fig. 11 is the summit of one of the many Drupes into which this fruit is usually divided. Each cell when not barren contains a single oblong slender seed; the cells in each drupe vary

assigned in the Economy of nature, to this family of sea-side plants, viz. to take the first possession of new-formed land, just emerging from the water, we see in the disposition of light buoyant fibres within the interior of these fruits, an arrangement peculiarly adapted to the office of vegetable colonization.* The sea-side locality of the Pandaneæ, causes many of their fruits to fall into the water, wherein they are drifted by the winds and waves, until they find a resting place upon some distant shore. A single drupe of Pandanus, thus charged with seeds, transports the elements of vegetation to the rising volcanic and coral islands of the modern Pacific. The seed thus stranded upon new-formed land, produces a plant which has peculiar provision for its support on a surface destitute of soil, by long and large aerial roots protruded above the ground around the lower part of its trunk. (See Pl. 63. Fig. 1.) These roots on reaching the ground are calculated to prop up the plant as buttresses surrounding the basis of the stem, so that it can maintain its erect position, and flourish in barren sand on newly elevated reefs, where little soil has yet accumulated.

from two to fourteen in number, and many of them are abortive, (Fig. 13.) The seeds within each drupe of Pandanus are enclosed in a hard nut, of which sections are given at Figs. 14, 15. These nuts are wanting in the Podocarya, whose seeds are smaller than those of Pandanex, and not collected into drupes, but dispersed uniformly in single cells over the entire circumference of the fruit. (See Pl. 63, Figs. 3, 8, 10.) The collection of the seeds into drupes surrounded by a hard nut, in the fruit of Pandanus, forms the essential difference between this genus, and our new genus, Podocarya.

In the fruit of Pandanus, Pl. 63, Figs. 11, 16, 17, the summit of each cell is covered with a hard cap or tubercle, irregularly hexagonal, and crowned at its apex with the remains of a withered stigma. We have a similar covering of hexagonal tubercles over the cells of Podocarya (Pl. 63, Figs. 2, a. 8, a. 10, a.) The remains of a stigma appear also in the centre of these hexagons above the apex of each seed. (Figs. 8, a. 10, a.)

* There is a similar provision for transporting to distant regions of the ocean, the seeds of the other family of sea-side plants which accompanies the Pandanus, in the buoyant mass of fibrous covering that surrounds the fruit of the Cocoa-nut,

380

VEGETABLES IN THE TERTIARY FORMATIONS.

We have as yet discovered no remains of the leaves, trunk of Pandaneæ in a fossil state, but the presence of o unique fruit in the Inferior Oolite formation near Charmou carries us back to a point of time, when we know fr other evidence that England was in the state of new-b land, emerging from the seas of a tepid climate; and sho that combinations of vegetable structure such as exist the modern Pandaneæ, adapted in a peculiar manner to office of vegetable colonization, prevailed also at the ti when the Oolite rocks were in process of formation.

This fruit also adds a new link to the chain of eviden which makes known to us the Flora of the Seconda periods of geology, and therein discloses fresh proofs Order, and Harmony, and of Adaptation of peculiar mea to peculiar ends; extending backwards from the actu condition of our Planet through the manifold stages change, which its ancient surface has undergone.*

SECTION IV.

VEGETABLES IN STRATA OF THE TERTIARY SERIES.†

Ir has been stated that the vegetation of the Tertiar period presents the general character of that of our exis ing Continents within the Temperate Zone. In Strata this Series, Dicotyledonous Plants assume nearly the sam proportions as at present, and are four or five times mor numerous than the Monocotyledonous; and the greate number of fossil Plants, although of extinct species, hav much resemblance to living Genera.

* Fruits of another genus of Pandaneæ, to which Mr. Ad. Brongniart has given the name of Pandanocarpum, (Prodrome, p. 138,) occur together with fruits of Cocoa-nut, at an early period of the Tertiary formations, among the numerous fossil fruits that are found in the London clay of the Isle of Shep pey.

+ See Pl. 1, Figs. 66 to 72.

« AnteriorContinuar »