period, beneath whose shade flourished the lesser ferns and associated plants.

The fruit of the living Club-mosses is an oval or cylindrical cone, which in some species forms an imbricated spike at the extremity of the branches; and there are numerous fossil fruits of this kind found together with the stems and leaves of the Lepidodendra, and in some instances attached to the branches; they have received the name of Lepidostrobi, or scaly-cones.*

Besides being preeminently a coal-plant, the Lepidodendron is found in the Devonian strata of the United States, of Caithness, and Thuringia; and in the Mountainlimestone of Northumberland.† It occurs also in strata of Carboniferous or Devonian age, both in Australia and South Africa.

LIGN. 178.-Transverse section of a

portion of the stem of a recent Pine (Pinus strobus,, highly mag

nified.

Long narrow branches, covered with numerous small leaves or bracts, occur in the coal-measures, which are regarded as being fossil forms of club-mosses, and are termed Lycopodites. Similar plant-remains have been found in the Tertiary and Oolitic strata, and some of these have been correctly referred to the Coniferæ. Indeed, the Dacrydium cupressinum of New Zealand, with its long pendant lycopodial branches and regularly scarred stem, and other similar conifers, should remind us that the

* Pict. Atlas, pl. ix. f. 1, and pl. xxxiii.; and Medals of Creation, Lign. 40. The structure aud affinities of the Lepidostrobi are well worked out and illustrated by Dr. Hooker, in the Mem. Geol. Surv. vol. ii., where Lepidodendron, Sigillariæ, and Calamites, &c., are also made the subjects of elucidation.

Tate, Fossil Flora of the Mountain Limestone, p. 297.

external form of one family of plants is imitated by another. It is from the fructification that the most decided characters of plants can alone be drawn.

39. CARBONIFEROUS TREES AND PLANTS.*-It was formerly supposed that no vestiges of coniferous plants and trees, which occur so abundantly in the secondary formations, were present in the coal; but Mr. Witham, by microscopical examination, ascertained that trees of this type constituted no inconsiderable portion of the flora of the carboniferous epoch; and remains of this order have since been detected in the Devonian and every formation of later origin. The recent coniferæ are arborescent, dividing into numerous branches, which are disposed in most genera with considerable regularity. The transverse sections of the wood exhibit concentric annual lines of growth (as in Lign. 178), and the vertical show the sides of the woody fibres studded with little pores or spots (Lign. 179).

00000000

Some of the fossil trees resemble

the European pines in their internal structure: but the greater number belong to the Araucarian type, which is characterized by the rows of spots being disposed, when double, not side by side, as in Lign. 179, but alternately, as we have

LIGN. 179.—Longitudinal section of previously explained (p. 713).†

pine-wood, parallel to a medullary

ray; showing the rows of spots or pores.

The coniferous trees of the coal have but few and slight appearances

of the lines by which the annual layers are separated, and resemble in this respect the existing species of tropical regions;

* Medals, p. 164, &c.

In the Royal Gardens at Kew, there are several flourishing trees of the A. excelsa, and other kinds of Araucaria.

Witham, op. cit.; and Quekett, Catalog. Foss. Veget. Hunterian Museum, pp. 27 and 28.

we may therefore infer that the seasons of the countries where the coal-plants flourished were subject to but little diversity, and that the changes of temperature were not abrupt.

In a quarry at Craigleith, near Edinburgh, at a depth of 140 feet, part of the trunk of a very large coniferous tree was discovered: its length was thirty-six feet, and the circum. ference of the base nine feet. Polished sections of this stem beautifully display the coniferous structure. A tree fiftynine feet long, traversing twelve beds of sandstone, has since been exposed; and, as is commonly the case, the bark was carbonized, and the woody stem was in some parts in the state of sandstone, and in others silicified.

Numerous seed-vessels have been found in the coal-measures, and are known as Cardiocarpon, Rhabdocarpos, Carpolites, and Trigonocarpon. The relations of these fruits are mostly very obscure.* The Trigonocarpa have been referred by some to palms, and by others to Cycads; but Dr. Hooker has shown † that, although certainly having characters of structure as closely related to the Cycads as to the Conifers, yet it is to the latter that the weight of the evidence tends to refer them; and he especially points to the peculiar coniferous genus Salisburia (a native of China), as presenting a fructification similar to that found in Trigonocarpon. Dr. Hooker mentions also that, as Dr. Lindley has pointed out, the foliage of Salisburia also affords a modern analogy, for the fossil leaves called Næggerathia, which, with some Trigonocarpon-like bodies, M. Brongniart has referred to the Cycadaceæ.

Dr. Hooker has described a fragment of cycadeous wood from the Durham coal-field; ‡ and in 1844, M. Goeppert had recognised in the carboniferous rocks of Europe four species of fossil plants which he considered referable to the Cycadaceæ.§

No well-authenticated remains of palms occur in the coalstrata.

* Fiedler; Foss. Frücht. &c. 1857. † Proc. Roy. Soc. vol. vii. p. 28. Mem. Geol. Survey, vol. ii. part 2, p. 421.

§ Annals Nat. Hist. vol. xv. p. 442. For figures and descriptions of recent and fossil cycadeous plants, see Buckland's Bridg. Treat. p. 494, and Medals, p. 150

40. FLORA OF THE COAL. A more extended notice of the fossil plants of the carboniferous system is not within the scope of these Lectures, and we will now take a brief review of the principal facts that have been submitted to our notice. We have seen that the most remarkable character of the flora of that remote epoch, is the immense numerical ascendance of certain peculiar tribes of cryptogamic plants, which amount to at least two-thirds of the whole of the species

Fig. 1. Araucaria (Gymnogen). 2. Pandanus (Endogen). 3. Arborescent Fern (Acrogen). 4. Lepidodendron (fossil).

hitherto determined. With these are associated some coniferæ, a few cycadaceæ, and some rare phanerogamic plants. The vast preponderance and magnitude of the vegetables bearing an analogy to the tribes both of acrogens and of gymnogens, but differing from existing species and genera, constitute,

therefore, the most important botanical feature. Thus we have plants related to the horsetail (Calamites), eighteen inches in circumference, and from thirty to forty feet high; arborescent club-mosses (Lepidodendra) attaining an altitude of sixty or seventy feet; other great lycopodiaceous trees (Sigillaria) fifty feet in height; besides tree-ferns, and a multitude of minor acotyledonous plants, with comparatively few coniferous trees. The contrast which such a flora presents to that afforded by the woods and forests of dicotyledonous trees, and the verdant turf, which now grow on the surface of the carboniferous districts of England, is as striking as the discrepancy between the zoology of the palæozoic formations and that of the present day. In Lign. 180, figs. 1, 3, and 4 represent some of the chief tree-like forms which flourished in the carboniferous era, namely, the coniferous Araucaria or Norfolk Island Pine (which is at the present day the best representative we have of some of the woody trees of the Carboniferous and Permian periods), the cryptogamic Tree-fern, and the lycopodiaceous Lepidodendron (no longer represented by living species). The Screw-palm or Pandanus, introduced in the sketch (Lign. 180, fig. 2) as an example of our endogenous tree, appears to have its earliest progenitors in the Jurassic period.

To arrive at any satisfactory conclusions as to the nature of the countries which supported the plants of the coal, we must consider, 1st, the geographical distribution of the related existing genera of plants, and the circumstances which conduce to their full development; and 2ndly, the probable hydrographical conditions of the earth's surface at the coalperiod. It is well known that a hot climate, humid atmosphere, and the unvarying temperature of the sea are the circumstances which exert the most favourable influence on the growth of Ferns and other cryptogamic plants; low islands in tropical latitudes being the localities where these forms of vegetation flourish most luxuriantly. From the relative proportion of land and water then probably existing in this region, we may infer that the countries in which the "carboniferous" flora grew were