2dly, that among these Cryptogamic plants, the Equisetaceæ attained a gigantic size; 3dly, that Dicotyledonous plants, which compose nearly two-thirds of living Vegetables, formed but a small proportion of the Flora of these early periods.* 4thly, that although many extinct genera, and certain families have no living representatives, and even

* The value to be attached to numerical proportions of fossil Plants, in estimating the entire condition of the Flora of these early periods, has been diminished by the result of a recent interesting experiment made by Prof. Lindley, on the durability of Plants immersed in water. (See Fossil Flora No. xvii. vol. iii. p. 4.) Having immersed in a tank of fresh-water, during more than two years, 177 species of plants, including representatives of all those which are either constantly present in the coal measures or universally absent, he found:

1. That the leaves and bark of most dicotyledonous Plants are wholly decomposed in two years, and that of those which do resist it, the greater part are Conifera and Cycadeœ.

2. That Monocotyledons are more capable of resisting the action of water, particularly Palms and Scitamineous Plants; but that Grasses and Sedges perish.

3. That Fungi, Mosses, and all the lowest forms of Vegetation disappear. 4. That Ferns have a great Power of resisting water if gathered in a green state, not one of those submitted to the experiment having disappeared, but that their fructification perished.

Although the results of this experiment in some degree invalidate the certainty of our knowledge of the entire Flora of each of the consecutive Periods of Geological History, it does not affect our information as to the number of the enduring Plants which have contributed to make up the Coal formation; nor as to the varying proportions, and changes in the species of Ferns and other plants, in the successive systems of vegetation that have clothed our globe.

It may be farther noticed, that as both trunks and leaves of Angiospermous dicotyledonous Plants have been preserved abundantly in the Tertiary formations, there appears to be no reason why, if Plants of this Tribe had existed during the Secondary and Transition Periods, they should not also occasionally have escaped destruction in the sedimentary deposites of these earlier epochs.

In Loudon's Mag. Nat. Hist. Jan. 1834, p. 34, is an account of some interesting experiments by Mr. Lukis, on successive changes in the form of the cortical and internal parts of the stems of succulent plants, (e. g. Sempervivum arboreum) during various stages of decay, which may illus trate analogous appearances in many fossil plants of the coal formation. VOL. I.-31

ceased to exist after the deposition of the Coal formation, yet are they connected with modern vegetables by common principles of structure, and by details of organization, which show them all to be parts of One grand, and consistent, and harmonious Design.

We may end our account of the Plants to which we have traced the origin of Coal, with a summary view of the various Natural changes, and processes in Art and Industry, through which we can follow the progress of this curious and most important vegetable production.

Few persons are aware of the remote and wonderful Events in the economy of our Planet, and of the complicated applications of human Industry and Science, which are involved in the production of the Coal that supplies with fuel the Metropolis of England. The most early stage to which we can carry back its origin, was among the swamps and forests of the primeval earth, where it flourished in the form of gigantic Calamites, and stately Lepidodendra, and Sigillariæ. From their native bed, these plants were torn away, by the storms and inundations of a hot and humid climate, and transported in some adjacent Lake, or Estuary, or Sea. Here they floated on the waters, until they sank saturated to the bottom, and being buried in the detritus of adjacent lands, became transferred to a new estate among the members of the mineral kingdom. A long interment followed, during which a course of Chemical changes, and new combinations of their vegetable elements, have converted them to the mineral condition of Coal. By the elevating force of subterranean Fires, these beds of Coal have been uplifted from beneath the waters, to a new position in the hills and mountains, where they are accessible to the industry of man. From this fourth stage in its adventures, our Coal has again been moved by the labours of the miner, assisted by the Arts and Sciences, that have co-operated to produce the Steam Engine and the Safety Lamp. Returned once more to the

light of day, and a second time committed to the waters, it has, by the aid of navigation, been conveyed to the scene of its next and most considerable change by fire; a change during which it becomes subservient to the most important wants and conveniences of Man. In this seventh stage of its long eventful history, it seems to the vulgar eye to undergo annihilation; its Elements are indeed released from the mineral combinations they have maintained for ages, but their apparent destruction is only the commencement of new successions of change and of activity. Set free from their long imprisonment, they return to their native Atmosphere, from which they were absorbed to take part in the primeval vegetation of the Earth. To-morrow, they may contribute to the substance of timber, in the Trees of our existing forests; and having for a while resumed their place in the living vegetable kingdom, may, ere long be plied a second time to the use and benefit of man. And when decay or fire shall once more consign them to the earth, or to the atmosphere, the same Elements will enter on some farther department, of their perpetual ministration, in the economy of the material world.

Fossil Coniferæ.*

ap

The Coniferæ form a large and very important tribe among living plants, which are characterized, not only by peculiarities in their fructification (as Gymnospermous phanerogamiæ,t) but also by certain remarkable arrangements

* See Pl. 1. Figs. 1. 31. 32. 69.

+ We owe to Mr. Brown, the important discovery, that Coniferæ and Cycadeæ are the only two families of plants that have their seeds originally naked, and not enclosed within an Ovary. (See Appendix to Captain King's Voyage to Australia.) They have for this reason been arranged in a distinct order, as Gymnospermous Phanerogamiæ. This peculiarity in the Ovulum is accompanied throughout both these families, by peculiarities in the internal structure of their stems, in which they differ from almost all dicotyledonous plants, and in some respects also from each other.

in the structure of their wood, whereby the smallest fragment may be identified.

Recent microscopic examinations of fossil woods have led to the recognition of an internal structure, resembling that of existing Coniferæ, in the trunks of large trees, both in the Carboniferous series,* and throughout the Secondary formations; and M. Ad. Brongniart has enumerated twenty species of fossil Coniferæ in strata of the Tertiary series. Many of these last approach more closely to existing Genera than those in the Secondary strata, and some are referable to them.

It has been farther shown by Nicol, (Edin. New Phil. Journal, January, 1834) that some of the most ancient fossil Coniferæ may be referred to the existing genus Pinus, and others to that of Araucaria; the latter of these comprehends some of the tallest among living trees, (See Pl. 1, Fig.

The recognition of these peculiar characters in the structure of the stem, is especially important to the Geological Botanist, because the stems of plants are often the only parts which are found preserved in a fossil

state.

* The occurrence of large coniferous trees in strata of the great Coal formation, was first announced in Mr. Witham's Fossil Vegetables, 1831. It was here stated that the higher and more complex organizations of Coniferæ exists in the Coal fields of Edinburgh and Newcastle, in strata which till lately have been supposed to contain only the simpler forms of vegetable

structure.

In the lower region of the Secondary strata, M. Ad. Brongniart has enumerated, among the fossil plants of the New red sand-stone of the Vosges, four species of Voltzia, a new genus of Coniferæ, having near affinities to the Araucaria and Cunninghamia. Branches, leaves, and cones of this genus are most abundant at Sultz les Bains, near Strasburgh.

Mr. Witham reckons eight species of Coniferæ among the fossil woods of the Lias; and five species, of which four are allied to the existing genus Thuia, occur in the Oolite formation of Stonesfield. (See Ad. Brongniart's Prod. p. 200.) For figures of Cones from the Lias and Greensand near Lyme Regis, and the Inferior oolite of Northamptonshire, see Lindly and Hutton's Fossil Flora, Plates 89, 135, 137.

"

Dr. Fitton has described and figured two very beautiful and perfect cones, one from Purbeck? and one from the Hastings sand. Geol. Trans. 2d. Series, Vol, iv. Pl. 22, Figs. 9, 10, p. 181 and 230.

1) and is best known in the Araucaria excelsa, or Norfolk Island Pine.

These discoveries are highly important, as they afford examples among the earliest remains of vegetable life, of identity in minute details of internal organization, between the most ancient trees of the primeval forests of our globe, and some of the largest living Coniferæ.*

The structure of Araucarias alone has been as yet iden

• The transverse section of any coniferous wood in addition to the radiating and concentric lines represented Pl. 56a, Fig. 7, exhibits under the microscope a system of reticulations by which coniferæ are distinguishable from other plants. The form of these reticulations magnified 400 times is given in Pl. 56a, Figs. 2, 4, 6. These apertures are transverse sections of the same vessels, which are seen in a longitudinal section at Pl. 56a; Fig. 8, cut from the centre towards the bark, and parallel to the medullary rays. These vessels exhibit a characteristic and beautiful structure, whereby a distinction is marked between the true Pines and Araucarias. In such a section the small and uniform longitudinal vessels, (Pl. 56a, Fig. 8) which constitute the woody fibre, present at intervals a remarkable appearance of small, nearly circular figures disposed in vertical rows (See Pl. 56a, Figs. 1, 3, 5.) These objects under the name of glands or discs, are differently arranged in different species; they are generally circular, but sometimes elliptical, and when near each other, become angular. Each of these discs has near its centre a smaller circular areola. Pl. 56a, Fig. 1, represents their appearance in the Pinus strobus of North America.

In some Coniferæ, the discs are in single rows; in others, in double as well as single rows, e. g. in Pinus strobus, Pl. 56a, Fig. 1.

Throughout the entire genus of the living Pines, when double rows of discs occur in one vessel, the discs of both rows are placed side by side, and never alternate, and the number of the rows of discs is never more than two.

In the Araucarias the groups of discs are arranged in single, double, triple and sometimes quadruple rows, see Pl. 56, Fig, 3. 5. They are much smaller than those in the true Pines, scarcely half their size, and in the double rows they always alternate with each other, and are sometimes circular, but mostly polygonal. Mr. Nicol has counted a row of not less than fifty discs in a length the twentieth part of an inch, the diameter of each disc not exceeding the thousandth part of an inch; but even the smallest of these are of enormous size, when compared with the fibres of the partitions bounding the vessels in which they occur.