Chapter 4

[AN]According to Newberry, lower part of Waverly group.

[AO]Traquariais to be distinguished from the calcareous bodies found in the corniferous limestone of Kelly’s Island, which I have described in the “Canadian Naturalist” asSaccamina Eriana, and believe to be Foraminiferal tests. They have since been described by Ulrich under a different name (Moellerina: contribution to “American Palæontology,” 1886). See Dr. Williamson’s papers in “Transactions of Royal Society of London.”

The true “Sporangites,” on the contrary, are round and smooth, with thick bituminous walls, which are punctured with minute transverse pores. In these respects, as already stated, they closely resemble the bodies found in the Australian white coal and Tasmanite. The precise geological age of this last material is not known with certainty, but it is believed to be Palæozoic.

With reference to the mode of occurrence of these bodies, we may note first their great abundance and wide distribution. The horizontal range of the bed at Kettle Point is not certainly known, but it is merely a northern outlier of the great belt of Erian shales referred to by Prof. Orton, and which extends, with a breadth of ten to twenty miles, and of great thickness, across the State of Ohio, for nearly two hundred miles. This Ohio black shale, which lies at the top of the Erian or the base of the Carboniferous, though probably mainly of Erian age, appears to abound throughout in these organisms, and in some beds to be replete with them. In like manner, in Brazil, according to Mr. Derby, these organisms are distributed over a wide area and throughout a great thickness of shale holdingSpirophyton, and apparently belonging to the Upper Erian. The recurrence of similar forms in the Tasmanite and white coal of Tasmania and Australia is another important fact of distribution. To thiswe may add the appearance of these macrospores in coals and shales of the Carboniferous period, though there in association with other forms.

It is also to be observed that the Erian shales, and the Forest of Dean beds described by Wethered, are marine, as shown by their contained fossils; and, though I have no certain information as to the Tasmanite and Australian white coal, they would seem, from the description of Milligan, to occur in distinctly aqueous, possibly estuarine, deposits. Wethered has shown that the discs described by Huxley and Newton in the Better-bed coal occur in the earthy or fragmentary layers, as distinguished from the pure coal. Those occurring in cannel coal are in the same case, so that the general mode of occurrence implies water-driftage, since, in the case of bodies so large and dense, wind-driftage to great distances would be impossible.

These facts, taken in connection with the differences between these macrospores and those of any known land-plant of the Palæozoic, would lead to the inference that they belonged to aquatic plants, and these vastly abundant in the waters of the Erian and Carboniferous periods.

It is still further to be observed that they are not, in the Erian beds, accompanied with any remains of woody or scalariform tissues, such as might be expected in connection with thedébrisof terrestrial acrogens, and that, on the other hand, we find them enclosed in cellular sporocarps, though in the majority of cases these have been removed by dehiscence or decay.

These considerations, I think, all point to the probability which I have suggested in my papers on this subject referred to above, that we have in these objects the organs of fructification of plants belonging to the orderRhizocarpeæ, or akin to it. The comparisons which I have instituted with the sporocarps and macrospores of these plants confirm this suggestion. Of the modernspecies which I have had an opportunity to examine,Salvinia natansof Europe perhaps presents the closest resemblance. In this plant groups of round cellular sporocarps appear at the bases of the floating fronds. They are about a line in diameter when mature, and are of two kinds, one containing macrospores, the other microspores or antheridia. The first, when mature, hold a number of closely packed globular or oval sporangia of loose cellular tissue, attached to a central placenta. Each of these sporangia contains a single macrospore, perfectly globular and smooth, with a dense outer membrane (exhibiting traces of lamination, and showing within an irregularly vacuolated or cellular structure, probably a prothallus). I cannot detect in it the peculiar pores which appear in the fossil specimens. Each macrospore is about one-seventieth of an inch in diameter when mature. The sporocarps of the microspores contain a vastly greater number of minute sporangia, about one two-hundredths of an inch in diameter. These contain disc-like antheridia, or microspores of very minute size.

The discs from Kettle Point and from the Ohio black shale, and from the shale boulders of the Chicago clays, are similar to the macrospores ofSalvinia, except that they have a thicker wall and are a little less in diameter, being about one-eightieth of an inch. The Brazilian sporocarps are considerably larger than those of the modernSalvinia, and the macrospores approach in size to those of the modern species, being one seventy-fifth of an inch in diameter. They also seem, like the modern species, to have thinner walls than those from Canada, Ohio, and Chicago. No distinct indication has been observed in the fossil species of the inner Sporangium ofSalvinia. Possibly it was altogether absent, but more probably it is not preserved as a distinct structure.

With reference to the microspores ofSalvinia, it is to be observed that the sporocarps, and the contained sporesor antheridia, are very delicate and destitute of the dense outer wall of the macrospores. Hence such parts are little likely to have been preserved in a fossil state; and in the Erian shales, if present, they probably appear merely as flocculent carbonaceous matter not distinctly marked, or as minute granules not well defined, of which there are great quantities in some of the shales.

The vegetation appertaining to the Sporangites has not been distinctly recognised. I have, however, found in one of the Brazilian specimens two sporocarps attached to what seems a fragment of a cellular frond, and numerous specimens of the supposed Algæ, namedSpirophyton, are found in the shales, but there is no evidence of any connection of this plant with theProtosalvinia.

Modern Rhizocarps present considerable differences as to their vegetative parts. Some, likePilularia, have simple linear leaves; others, likeMarsilea, have leaves in whorls, and cuneate in form; while others, likeAzollaandSalvinia, have frondose leaves, more or less pinnate in their arrangement. If we inquire as to fossils representing these forms of vegetation, we shall find that some of the plants to be noticed in the immediate sequel may have been nearly allied to the Rhizocarps. In the mean time I may state that I have proposed the generic nameProtosalviniafor these curious macrospores and their coverings, and have described in the paper in the “Bulletin of the Chicago Academy of Sciences,” already quoted, five species which may be referred to this genus.

These facts lead to inquiries as to the origin of the bituminous matter which naturally escapes from the rocks of the earth as petroleum and inflammable gas, or which may be obtained from certain shales in these forms by distillation. These products are compounds of carbon and hydrogen, and may be procured from recent vegetable substances by destructive distillation. Some vegetable matters, also, are much richer in carbon and hydrogenthan others, and it is a remarkable fact that the spores of certain cryptogamous plants are of this kind, as we see in the inflammable character of the dry spores of Lycopodium; and we know that the slow putrefaction of such material underground effects chemical changes by which bituminous matter can be produced. There is, therefore, nothing unreasonable in the supposition advanced by Prof. Orton, that the spores so abundantly contained in the Ohio black shales are important or principal sources of the bituminous matter which they contain. Microscopic sections of this shale show that much of its material consists of the rich bituminous matter of these spores (Fig. 16). At the same time, while we may trace the bitumen of these shales, and of some beds of coal, to this cause, we must bear in mind that there are other kinds of bituminous rocks which show no such structures, and may have derived their combustible material from other kinds of vegetable matter, whether of marine or of land plants. We shall better understand this when we have considered the origin of coal.

The macrospores above referred to may have belonged to humble aquatic plants mantling the surfaces of water or growing up from the bottom, and presenting little aërial vegetation. But there are other Erian plants, as already mentioned, which, while of higher structure, may be of Rhizocarpean affinities.

One of these is the beautiful plant with whorls of wedge-shaped leaves, to which the nameSphenophyllum(seeFig. 20) has been given. Plants referred to this genus have been described by Lesquereux from the upper part of the Siluro-Cambrian,[AP]and a beautiful little species occurs in the Erian shales of St. John, New Brunswick.[AQ]The genus is also continued, and is still moreabundant, in the Carboniferous. Many years ago I observed, in a beautiful specimen collected by Sir W. E. Logan, in New Brunswick, that the stem of this plant had an axis of reticulated and scalariform vessels, and an outer bark.[AR]Renault and Williamson have more recently obtained more perfect specimens, and the former has figured a remarkably complex triangular axis, containing punctate and barred vessels, and larger punctate vessels filling in its angles. Outside of this there is a cellular inner bark, and this is surrounded by a thick fibrous envelope. That a structure so complex should belong to a plant so humble in its affinities is one of the strange anomalies presented by the old world, and of which we shall find many similar instances. The fruit ofSphenophyllumwas borne in spikes, with little whorls of bracts or rudimentary leaves bearing round sporocarps.

[AP]“American Journal of Science.”

[AQ]Dawson, “Report on Devonian Plants,” 1870.

[AR]“Journal of the Geological Society,” 1865.

Fig. 17.—Ptilophyton plumosum(Lower Carboniferous, Nova Scotia). Natural size and magnified.

A second type of plant, which may have been Rhizocarpean in its affinities, is that to which I have given the namePtilophyton.[AS]It consists of beautiful featheryfronds, apparently bearing on parts of the main stem or petiole small rounded sporocarps. They are found abundantly in the Middle Erian of the State of New York, and also occur in Scotland, while one species appears to occur in Nova Scotia, as high as the Lower Carboniferous (Figs.17,18).

[AS]Plumalinaof Hall.

Fig. 18.—Ptilophyton Thomsoni(Scotland),a, Impression of plant in vernation,b, Branches conjecturally restored,c, Branches ofLycopodites Milleri, on same slab.

These organisms have been variously referred to Lycopods, to Algæ, or to Zoöphytes, but an extended comparison of American and Scottish specimens has led me to the belief that they were aquatic plants, more likely to have been allied to Rhizocarps than to any other group. Some evidence of this will be given in a note appended to this chapter.

Fig. 19.—Psilophyton princeps, restored (Lower Erian, Gaspé).a, Fruit, natural size.b, stem, natural size,c, Scalariform tissue of the axis, highly magnified. In the restoration, one side is represented in vernation and the other in fruit.

Another genus, which I have namedPsilophyton[AT](Figs.19,21), may be regarded as a connecting link between the Rhizocarps and the Lycopods. It is so named from its resemblance, in some respects, to the curious parasitic Lycopods placed in the modern genusPsilotum. Several species have been described, and they are eminently characteristic of the Lower Erian, in which they were first discovered in Gaspé. The typical species,Psilophyton princeps, which fills many beds of shale and sandstone in Gaspé Bay and the head of the neighbouring Bay des Chaleurs with its slender stems and creeping, cord-like rhizomes, may be thus described:

[AT]“Journal of the Geological Society,” vols, xv., xviii., and xix., “Report on Devonian Plants of Canada,” 1871.

Stems branchingdichotomously, and covered with interrupted ridges. Leaves rudimentary, or short, rigid, and pointed; in barren stems, numerous and spirally arranged; in fertile stems and branchlets, sparsely scattered or absent; in decorticated specimens, represented by a minute punctate scars. Young branches circinate; rhizomata cylindrical, covered with hairs or ramenta, and having circular areoles irregularly disposed, giving origin to slender cylindrical rootlets. Internal structure—an axis of scalariform vessels, surrounded by a cylinder of parenchymatous cells, and by an outer cylinder of elongated woody cells. Fructification consisting of naked oval spore-cases, borne usually in pairs on slender, curved pedicels, either lateral or terminal.

Fig. 20.—Sphenophyllum antiquum(Erian, New Brunswick). See pp.61,67.

This species was fully described by me in the papers referred to above, from specimens obtained from the rich exposures at Gaspé Bay, and which enabled me to illustrate its parts more fully, perhaps, than those of any other species of so great antiquity. In the specimens I had obtained I was able to recognise the forms of the rhizomata, stems, branches, and rudimentary leaves, and also the internal structure of the stems and rhizomata, and to illustrate the remarkable resemblance of the forms and structures to those of the modernPsilotum. The fructification was, however, altogether peculiar, consisting of narrowly ovate sporangia, borne usually in pairs, on curved and apparently rigid petioles. Under the microscope these sporangia show indications of cellular structure, and appear to have been membranous in character. In some specimens dehiscence appears to have taken place by a slit in one side, and, clay having entered into the interior, both walls of the spore-case can be seen. In other instances, being flattened, they might be mistakenfor scales. No spores could be observed in any of the specimens, though in some the surface was marked by slight, rounded prominences, possibly the impressions of the spores within. This peculiar and very simple style of spore-case is also characteristic of other species, and gives toPsilophytona very distinct generic character. These naked spore-cases may be compared to those of such lycopodiaceous plants asPsilotum, in which thescales are rudimentary. They also bear some resemblance, though on a much larger scale, to the spore-cases of some Erian ferns (Archæopteris), to be mentioned in the sequel. On the whole, however, they seem most nearly related to the sporocarps of the Rhizocarpeæ.

Fig. 21.—LepidodendronandPsilophyton(Erian, New Brunswick). A,Lepidodendron Gaspianum. B, C,Psilophyton elegans.

Arthrostigma, which is found in the same beds with Psilophyton, was a plant of more robust growth, with better-developed, narrow, and pointed leaves, borne in a verticillate or spiral manner, and bearing at the ends of its branches spikes of naked sporocarps, apparently similar to those ofPsilophytonbut more rounded in form. The two genera must have been nearly related, and the slender branchlets ofArthrostigmaare, unless well preserved, scarcely distinguishable from the stems ofPsilophyton.[AU]

[AU]Reports of the author on “Devonian Plants,” “Geological Survey of Canada,” which see for details as to Erian Flora of northeastern America.

If, now, we compare the vegetation of these and similar ancient plants with that of modern Rhizocarps, we shall find that the latter still present, though in a depauperated and diminished form, some of the characteristics of their predecessors. Some, likePilularia, have simple linear leaves; others, likeMarsilea, have leaves in verticils and cuneate in form; while others, like Azolla and Salvinia, have frondose leaves, more or less pinnate in their arrangement. The first type presents little that is characteristic, but there are in the Erian sandstones and shales great quantities of filamentous and linear objects which it has been impossible to refer to any genus, and which might have belonged to plants of the type ofPilularia. It is quite possible, also, that such plants asPsilophyton glabrumandCordaites angustifolia, of which the fructification is quite unknown, may have been allied to Rhizocarps. With regard to the verticillate type, we are at once reminded ofSphenophyllum(Fig. 20), whichmany palæobotanists have referred to theMarsiliacæ, though, like other Palæozoic Acrogens, it presents complexities not seen in its modern representatives.S. primævumof Lesquereux is found in the Hudson River group, and myS. antiquumin the Middle Erian. Besides these, there are in the Silurian and Erian beds plants with verticillate leaves which have been placed with the Annulariæ, but which may have differed from them in fructification.Annularia laxa, of the Erian, andProtannularia Harknessii, of the Siluro-Cambrian, may be given as examples, and must have been aquatic plants, probably allied to Rhizocarps. It is deserving of notice, also, that the two best-known species ofPsilophyton(P. princepsandP. robustius), while allied to Lycopods by the structure of the stem and such rudimentary foliage as they possess, are also allied, by the form of their fructification, to the Rhizocarps, and not to ferns, as some palæobotanists have incorrectly supposed. A similar remark applies toArthrostigma; and the beautiful pinnately leavedPtilophytonmay be taken to represent that type of foliage as seen in modern Rhizocarps, while the allied forms of the Carboniferous which Lesquereux has namedTrochophyllum, seem to have had sporocarps attached to the stem in the manner ofAzolla.

The whole of this evidence, I think, goes to show that in the Erian period there were vast quantities of aquatic plants, allied to the modern Rhizocarps, and that the so-calledSporangitesreferred to in this paper were probably the drifted sporocarps and macrospores of some of these plants, or of plants allied to them in structure and habit, of which the vegetative organs have perished. I have shown that in the Erian period there were vast swampy flats covered withPsilophyton, and in similar submerged tracts near to the sea theProtosalviniamay have filled the waters and have given off the vast multitudes of macrospores which, drifted by currents, have settled in themud of the black shales. We have thus a remarkable example of a group of plants reduced in modern times to a few insignificant forms, but which played a great role in the ancient Palæozoic world.

Leaving the Rhizocarps, we may now turn to certain other families of Erian plants. The first to attract our attention in this age would naturally be the Lycopods, the club-mosses or ground-pines, which in Canada and the Eastern States carpet the ground in many parts of our woods, and are so available for the winter decoration of our houses and public buildings. If we fancy one of these humble but graceful plants enlarged to the dimensions of a tree, we shall have an idea of aLepidodendron, or of any of its allies (Figs.15,21). These large lycopodiaceous trees, which in different specific and generic forms were probably dominant in the Erian woods, resembled in general those of modern times in their fruit and foliage, except that their cones were large, and probably in most cases with two kinds of spores, and their leaves were also often very long, thus bearing a due proportion to the trees which they clothed. Their thick stems required, however, more strength than is necessary in their diminutive successors, and to meet this want some remarkable structures were introduced similar to those now found only in the stems of plants of higher rank. The cells and vessels of all plants consist of thin walls of woody matter, enclosing the sap and other contents of these sacs and tubes, and when strength is required it is obtained by lining their interior with successive coats of the hardest form of woody matter, usually known as lignin. But while the walls remain thin, they afford free passage to the sap to nourish every part. If thickened all over, they would become impervious to sap, and therefore unsuited to one of their most important functions. These two ends of strength and permeability are secured by partial linings of lignin, leaving portions ofthe original wall uncovered. But this may be done in a great variety of ways.

The most ancient of these contrivances, and one still continued in the world of plants, is that of the barred or scalariform vessel. This may be either square or hexagonal, so as to admit of being packed without leaving vacancies. It is strengthened by a thick bar of ligneous matter up each angle, and these are connected by cross-bars so as to form a framework resembling several ladders fastened together. Hence the namescalariform, or ladder-like. Now, in a modern Lycopod there is a central axis of such barred vessels associated with simpler fibres or elongated cells. Even inSphenophyllumandPsilophyton, already referred to as allied to Rhizocarps,[AV]there is such a central axis, and in the former rigidity is given to this by the vascular and woody elements being arranged in the form of a three-sided prism or three-rayed star. But such arrangements would not suffice for a tree, and hence in the arboreal Lycopods of the Erian age a more complex structure is introduced. The barred vessels were expanded in the first instance into a hollow cylinder filled in with pith or cellular tissue, and the outer rind was strengthened with greatly thickened cells. But even this was not sufficient, and in the older stems wedge-shaped bundles of barred tissue were run out from the interior, forming an external woody cylinder, and inside of the rind were placed bundles of tough bast fibres. Thus, a stem was constructed having pith, wood, and bark, and capable of additions to the exterior of the woody wedges by a true exogenous growth. The plan is, in short, the same with that of the stems of the exogenous trees of modern times, except that the tissues employed are less complicated. The structures of these remarkabletrees, and the manner in which they anticipate those of the true exogens of modern times, have been admirably illustrated by Dr. Williamson, of Manchester. His papers, it is true, refer to these plants as existing in the Carboniferous age, but there is every reason to believe that they were of the same character in the Erian. The plan is the same with that now seen in the stems of exogenous phænogams, and which has long ceased to be used in those of the Lycopods. In this way, however, large and graceful lycopodiaceous trees were constructed in the Erian period, and constituted the staple of its forests.

[AV]First noticed by the author, “Journal of Geological Society,” 1865; but more completely by Renault, “Comptes Rendus,” 1870.

The roots of these trees were equally remarkable with their stems, and so dissimilar to any now existing that botanists were long disposed to regard them as independent plants rather than roots. They were similar in general structure to the stems to which they belonged, but are remarkable for branching in a very regular manner by bifurcation like the stems above, and for the fact that their long, cylindrical rootlets were arranged in a spiral manner and distinctly articulated to the root after the manner of leaves rather than of rootlets, and fitting them for growing in homogeneous mud or vegetable muck. They are the so-calledStigmariaroots, which, though found in the Erian and belonging to its lycopodiaceous plants, attained to far greater importance in the Carboniferous period, where we shall meet with them again.

Fig. 22.—Erian ferns (New Brunswick), A,Aneimites obtusa. C,Neuropteris polymorpha. F,Sphenopteris pilosa. N,Hymenophyllites subfurcatus.

There were different types of lycopodiaceous plants in the Erian. In addition to humble Lycopods like those of our modern woods and great Lepidodendra, which were exaggerated Lycopods, there were thick-stemmed and less graceful species with broad rhombic scars (Leptophleum), and others with the leaf-scars in vertical rows (Sigillaria), and others, again, with rounded leaf-scars, looking like the marks on Stigmaria, and belonging to the genusCyclostigma. Thus some variety was given to the arboreal club-mosses of these early forests. (SeeFig. 15.)

Another group of plants which attained to great development in the Erian age is that of the Ferns or Brackens. The oldest of these yet known are found in the Middle Erian. TheEopterisof Saporta, from the Silurian, at one time supposed to carry this type much further back, has unfortunately been found to be a mere imitative form, consisting of films of pyrites of leaf-like shapes, and produced by crystallisation. In the Middle Erian, however, more especially in North America, many species have been found (Figs.22to24).[AW]I have myself recorded more than thirty species from the Middle Erian of Canada, and these belong to several of the genera found in the Carboniferous, though some are peculiar to the Erian. Of the latter, the best known are perhaps those of the genusArchæopteris(Fig. 24), so abundant in the plant-beds of Kiltorcan in Ireland, as well as in North America. In this genus the fronds are large and luxuriant, with broad obovate pinnules decurrent, on the leaf-stalk, and with simple sac-like spore-cases borne on modified pinnæ. Another very beautiful fern found withArchæopterisis that which I have namedPlatyphyllum, and which grew on a creeping stem or parasitically on stems of other plants, and had marginal fructification.[AX]Another very remarkable fern, which some botanists have supposed may belong to a higher group than the ferns, is Megalopteris (Fig. 26).

[AW]For descriptions of these ferns, see reports cited above.

[AX]“Reports on Fossil Plants of the Devonian and Upper Silurian of Canada,” 1871, &c.

Fig. 23.—Erian ferns (New Brunswick), B,Cyclopteris valida, and pinnule enlarged, D,Sphenopteris marginata, and portion enlarged. E,Sphenopteris Harttii. G,Hymenophyllites curtilobus. H,Hymenophyllites Gersdorffii, and portion enlarged. I,Alethopteris discrepans, K,Pecopteris serrulata, L,Pecopteris preciosa. M,Alethopteris Perleyi.

Fig. 24.—Archæopteris Jacksoni, Dawson (Maine). An Upper Erian fern,a,b, Pinnules showing venation.

Fig. 25.—An Erian tree-fern.Caulopteris Lockwoodi, Dawson, reduced. (From a specimen from Gilboa, New York.)

Some of the Erian ferns attained to the dimensions of tree-ferns. Large stems of these, which must have floated out far from land, have been found by Newberry in the marine limestone of Ohio (Caulopteris antiquaandC. peregrina, Newberry),[AY]and Prof. Hall has found in the Upper Devonian of Gilboa, New York, the remains of a forest of tree-ferns standingin situwith their great masses of aërial roots attached to the soil in which they grew (Caulopteris Lockwoodi, Dn.).[AZ]

[AY]“Journal of the Geological Society,” 1871.

[AZ]Ibid.

Fig. 26.—Megalopteris Dawsoni, Hartt (Erian, New Brunswick),a, Fragment of pinna.b, Point of pinnule,c, Venation, (The midrib is not accurately given in this figure.)

These aërial roots introduce us to a new contrivance for strengthening the stems of plants by sending out into the soil multitudes of cord-like cylindrical roots fromvarious heights on the stem, and which form a series of stays like the cordage of a ship. This method of support still continues in the modern tree-ferns of the tropics and the southern hemisphere. In one kind of tree-fernstem from the Erian of New York, there is also a special arrangement for support, consisting of a series of peculiarly arranged radiating plates of scalariform vessels, not exactly like those of an exogenous stem, but doing duty for it (Asteropteris)[BA]Similar plants have been described from the Erian of Falkenberg, in Germany, and of Saalfeld, in Thuringia, by Goeppert and Unger, and are referred to ferns by the former, but treated as doubtful by the latter,[BB]This peculiar type of tree-fern is apparently a precursor of the more exogenous type ofHeterangium, recently described and referred to ferns by Williamson. Here, again, we have a mechanical contrivance now restricted to higher plants appropriated by these old cryptogams.

[BA]“Journal of the Geological Society,” London, 1881.

[BB]“Sphenopteris Refracta,” Goeppert; “Flora des Uebergangsgebirges.” “Cladoxylon Mirabile,” Unger; “Palæontologie des Thuringer Waldes.”

Fig. 27.—Calamites radiatus(Erian, New Brunswick).

Fig. 28.—Asterophyllites (Erian, New Brunswick),A, Asterophyllites latifolia. B, Do.,apex of stem (?) fruit,C, C1,A. scutigera.D,A. latifolia, larger whorl of leaves. D1, Leaf.

The history of the ferns in geological time is remarkably different from that of the Lycopods; for while the latter have long ago descended from their pristine eminence to a very humble place in nature, the former still, in the southern hemisphere at least, retain their arboreal dimensions and ancient dominance.

The family of theEquisetaceæ, or mare’s-tails, was also represented by large species ofCalamitesand byAsterophyllitesin the Erian; but, as its headquarters are in the Carboniferous, we may defer its consideration till the next chapter. (Figs.27,28.)

Passing over these for the present, we find that the flowering plants are represented in the Erian forests by at least two types of Gymnosperms, that ofTaxineæor yews, and an extinct family, that of theCordaites(Figs.30,31). The yew-trees are closely allied to the pines and spruces, and are often included with them in the family ofConiferæ. They differ, however, in the habit of producing berries or drupe-like fruits instead of cones, and there is some reason to believe that this was the habit of the Erian trees of this group, though their wood in some instances resembles rather that of the Araucaria, or NorfolkIsland pine, than that of the modern yews. These trees are chiefly known to us by their mineralised trunks, which are often found like drift-wood on modern sand-banks embedded in the Erian sandstones or limestones. It often shows its structure in the most perfect manner in specimens penetrated by calcite or silica, or by pyrite, and in which the original woody matter has been resolved into anthracite or even into graphite. These trees have true woody tissues presenting that beautiful arrangement of pores or thin parts enclosed in cup-like discs, which is characteristic of the coniferous trees, and which is a great improvement on the barred tissue already referred to, affording a far more strong, tough, and durable wood, such as we have in our modern pines and yews (Fig. 29).

Fig. 29.—Dadoxylon Ouangondianum, an Erian conifer, A, Fragment showing Sternberg pith and wood;a, medullary sheath;b, pith;c, wood;d, section of pith, B, Wood-cell;a, hexagonal areole;b, pore,c, Longitudinal section of wood, showing,a, areolation, andb, medullary rays, D, Transverse section, showing,a, wood-cells, andb, limit of layer of growth, (B, C, D, highly magnified.)

These primitive pines make their appearance in the Middle Erian, in various parts of America, as well as in Scotland and Germany, and they are represented by wood indicating the presence of several species. I have myself indicated and described five species from the Erian of Canada and the United States. From the fact that these trees are represented by drifted trunks embedded in sandstones and marine limestones, we may, perhaps, infer that they grew on the rising grounds of the Erian land, and that their trunks were carried by river-floods into the sea. No instance has yet certainly occurred of the discovery of their foliage or fruit, though there are some fan-shaped leaves usually regarded as ferns which may have belonged to such trees. These in that case would have resembled the modernGingkoof China, and some of the fruits referred to the genusCardiocarpummay have been produced by them. Various names have been given to these trees. I have preferred that given by Unger,Dadoxylon, as being more non-committal as to affinities than the others.[BC]Many of these trees had very long internal pith-cylinders, with curious transverse tubulæ, and which, when preserved separately, have been namedSternbergia.

[BC]Araucarites, Goeppert;Araucarioxylon, Kraus.

Allied to these trees, and perhaps intermediate between them and theCycads, were those known asCordaites(Fig. 30), which had trunks resembling those ofDadoxylon, but with still largerSternbergiapiths and an internal axis of scalariform vessels, surrounded by a comparatively thin woody cylinder. Some of them have leaves over a foot in length, reminding one of the leaves of broad-leaved grasses or iridaceous plants. Yet their flowers and fruit seem to have been more nearly allied to the yews than to any other plants (Fig. 31). Their stems were less woodyand their piths larger than in the true pines, and some of the larger-leaved species must have had thick, stiff branches. They are regarded as constituting a separate family, intermediate between pines and cycads, and, beginning in the Middle Devonian, they terminate in the Permian, where, however, some of the most gigantic species occur. In so far as the form and structure of the leaves, stems, and fruit are concerned, there is marvellously little difference between the species found in the Erian and the Permian. They culminated, however, in the Carboniferous period, and the coal-fields of southern France have proved so far the richest in their remains.

Fig. 30.—Cordaites Robbii(Erian, New Brunswick),a, Group of young leaves.b, Point of leaf,c, Base of leaf,d. Venation, magnified.

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