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THE PALÆONTOLOGICAL HISTORY OF PLANTS.

Palæontology, or the science of ancient organisms, deals, as its subject, with all the plants and animals of all the geologic periods. It bears nearly the same sort of relation to the physical history of the past, that biography does to the civil and political history of the past. For just as a complete biographic system would include every name known to the historian, a complete palæontologic system would include every fossil known to the geologist. It enumerates and describes all the organic existences of all the extinct creations—all the existences, too, of the present creation that occur in the fossil or semi-fossil form; and, thus coextensive in space with the earth's surface—nay, greatly more than coextensive with the earth's surface—for in the vast hieroglyphic record which our globe composes, page lies beneath page, and inscription covers over inscription—coextensive, too, in time, with every period in the terrestrial history since being first began upon our planet—it presents to the student a theme so vast and multifarious, that it might seem but the result, on his part, of a proper modesty, conscious of the limited range of his powers, and of the brief and fleeting term of his life, were he to despair of being ever able effectually to grapple with it. "But," to borrow from one of the most ingenious of our Scottish metaphysicians, "in this, as in other instances in which nature has given us difficulties with which to cope, she has not left us to be wholly overcome." "If," says Dr. Thomas Brown, in his remarks on the classifying principle—"if she has placed us in a labyrinth, she has at the same time furnished us with a clue which may guide us, not, indeed, through all its dark and intricate windings, but through those broad paths which conduct us into day. The single power by which we discover resemblance or relation in general, is a sufficient aid to us in the perplexity or confusion of our first attempts at arrangement. It begins by converting thousands, and more than thousands, into one; and, reducing in the same manner the numbers thus formed, it arrives at last at the few distinctive characters of those great comprehensive tribes on which it ceases to operate, because there is nothing left to oppress the memory or the understanding."

But, is this all? Can the Palæontologist but say that that classifying principle, which in every other department of science yields such assistance to the memory, is also of use in his, or but urge that it enables him to sort and arrange his facts; and that, by converting one idea into the type and exemplar of many resembling ones, it imparts to him an ability of carrying not inadequate conceptions of the mighty whole in his mind? If this were all, you might well ask, Why obtrude upon us, in connection with your special science, a common semi-metaphysical idea, equally applicable to all the sciences—in especial, for example, to that botany which is the science of existing plants, and to that zoology which is the science of existing animals? Nay, I reply, but it is not all. I refer to this classifying principle because, while it exists in relation to all other sciences as a principle—to use the words of the metaphysician just quoted—"given to us by nature,"—as a principle of the mind within—it exists in Palæontological science as a principle of nature itself—as a principle palpably external to the mind. It is a marvellous fact, whose full meaning we can as yet but imperfectly comprehend, that myriads of ages ere there existed a human mind, well nigh the same principles of classification now developed by man's intellect in our better treatises of zoology and botany, were developed on this earth by the successive geologic periods; and that the by-past productions of our planet, animal and vegetable, were chronologically arranged in its history, according to the same laws of thought which impart regularity and order to the works of the later naturalist and phytologists.

I need scarce say how slow and interrupted in both provinces the course of arrangement has been, or how often succeeding writers have had to undo what their predecessors had done, only to have their own classifications set aside by their successors in turn. At length, however, when the work appears to be well nigh completed, a new science has arisen, which presents us with a very wonderful means of testing it. Cowley, in his too eulogistic ode to Hobbes—smit by the singular ingenuity of the philosophic infidel, and unable to look through his sophisms to the consequences which they involved—could say, in addressing him, that

"only God could know

Whether the fair idea he did show

Agreed entirely with God's own or no."

And he then not very wisely added—

"This, I dare boldly tell,

'T is so like truth, 't will serve our turn as well."

We now know, however, that no mere resemblance to truth will for any considerable length of time serve its turn. It is because the resemblances have, like those of Hobbes, been mere resemblances, that so much time and labor have had to be wasted by the pioneers of science in their removal; and, now that a wonderful opportunity has occurred of comparing, in this matter of classification, the human with the Divine idea—the idea embodied by the zoologists and botanists in their respective systems, with the idea embodied by the Creator of all in geologic history—we cannot perhaps do better, in entering upon our subject, than to glance briefly at the great features in which God's order of classification, as developed in Palæontology, agrees with the order in which man has at length learned to range the living productions, plant and animal, by which he is surrounded, and of which he himself forms the most remarkable portion. In an age in which a class of writers not without their influence in the world of letters would fain repudiate every argument derived from design, and denounce all who hold with Paley and Chalmers as anthropomorphists, that labor to create for themselves a god of their own type and form, it may be not altogether unprofitable to contemplate the wonderful parallelism which exists between the Divine and human systems of classification, and—remembering that the geologists who have discovered the one had no hand in assisting the naturalists and phytologists who framed the other—soberly to inquire whether we have not a new argument in the fact for an identity in constitution and quality of the Divine and human minds—not a mere fanciful identity, the result of a disposition on the part of man to imagine to himself a God bearing his own likeness, but an identity real and actual, and the result of that creative act by which God formed man in his own image.

The study of plants and animals seems to have been a favorite one with thoughtful men in every age of the world. According to the Psalmist, these great "works of the Lord are sought out of all them that have pleasure therein." The Book of Job, probably the oldest writing in existence, is full of vivid descriptions of the wild denizens of the flood and desert; and it is expressly recorded of the wise old king, that he "spake of trees, from the cedar tree that is in Lebanon, even unto the hyssop that springeth out of the wall; and also of beasts, and of fowl, and of creeping things, and of fishes." Solomon was a zoologist and botanist; and there is palpable classification in the manner in which his studies are described. It is a law of the human mind, as has been already said, that, wherever a large stock of facts are acquired, the classifying principle steps in to arrange them. "Even the rudest wanderer in the fields," says Dr. Brown, "finds that the profusion of blossoms around him—in the greater number of which he is able himself to discover many striking resemblances—may be reduced to some order of arrangement." But, for many centuries, this arranging faculty labored but to little purpose. As specimens of the strange classification that continued to obtain down till comparatively modern times, let us select that of two works which, from the literary celebrity of their authors, still possess a classical standing in letters—Cowley's "Treatise on Plants," and Goldsmith's "History of the Earth and Animated Nature." The plants we find arranged by the poet on the simple but very inadequate principle of size and show. Herbs are placed first, as lowest and least conspicuous in the scale; then flowers; and, finally, trees. Among the herbs, at least two of the ferns—the true maidenhair and the spleenwort—are assigned places among plants of such high standing as sage, mint, and rosemary: among the flowers, monocotyledons, such as the iris, the tulip, and the lily, appear among dicotyledons, such as the rose, the violet, the sunflower, and the auricula: and among trees we find the palms placed between the plum and the olive; and the yew, the fir, and the juniper, flanked on one side by the box and the holly, and on the other by the oak. Such, in treating of plants, was the classification adopted by one of the most learned of English poets in the year 1657.

Nor was Goldsmith,-who wrote more than a century later, much more fortunate in dealing with the animal kingdom. Buffon had already published his great work; and even he could bethink him of no better mode of dividing his animals than into wild and tame. And in Goldsmith, who adopted, in treating of the mammals, a similar principle, we find the fishes and molluscs placed, in advance of the sauroid, ophidian, and batrachian reptiles—the whale united in close relationship to the sharks and rays—animals of the tortoise kind classed among animals of the lobster kind, and both among shell fish, such as the snail, the nautilus, and the oyster. And yet Goldsmith was engaged on his work little more than eighty years ago. In fine, the true principles of classification in the animal kingdom are of well nigh as recent development as geologic science itself, and not greatly more ancient in even the vegetable kingdom. It would, of course, be wholly out of place to attempt giving a minute history here of the progress of arrangement in either department; but it can scarce be held that the natural system of plants was other than very incomplete previous to 1789, when Jussieu first enunciated his scheme of classification; nor did it receive its later improvements until so late as 1846, when, after the publication, in succession, of the schemes of De Candolle and Endlicher, Lindley communicated his finished system to the world. And there certainly existed no even tolerably perfect system of zoology until 1816, when the "Animal Kingdom" of Cuvier appeared. Later naturalists—such as Agassiz, in his own special department, the history of fishes, and Professor Owen in the invertebrate divisions—have improved on the classification of even the great Frenchman; but for purposes of comparison between the scheme developed in geologic history and that at length elaborated by the human mind, the system of Cuvier will be found, for at least our present purpose, sufficiently complete. And in tracing through time the course of the vegetable kingdom, let us adopt, as our standard to measure it by, the system of Lindley.

Commencing at the bottom of the scale, we find the Thallogens, or flowerless plants which lack proper stems and leaves—a class which includes all the algæ. Next succeed the Acrogens, or flowerless plants that possess both stems and leaves—such as the ferns and their allies. Next, omitting an inconspicuous class, represented by but a few parasitical plants incapable of preservation as fossils, come the Endogens—monocotyledonous flowering plants, that include the palms, the liliaceæ, and several other families, all characterized by the parallel venation of their leaves. Next, omitting another inconspicuous tribe, there follows a very important class—the Gymnogens—polycotyledonous trees, represented by the conifers; and cycadaceæ. And, last of all, come the Dicotyledonous Exogens—a class to which all our fruit, and what are known as our "forest trees," belong, with a vastly preponderating majority of the herbs and flowers that impart fertility and beauty to our gardens and meadows. This last class, though but one, now occupies much greater space in the vegetable kingdom than all the others united.

Such is the arrangement of Lindley, or rather an arrangement the slow growth of ages, to which this distinguished botanist has given the last finishing touches. And let us now mark how closely it resembles the geologic arrangement as developed in the successive stages of the earth's history.

Fig. 1.[4] THE GENEALOGY OF PLANTS.

The most ancient period of whose organisms any trace remains in the rocks seems to have been, prevailingly at least, a period of Thallogens. We must, of course, take into account the fact, that it has yielded no land plants, and that the sea is everywhere now, as of old, the great habitat of the algæ—one of the four great orders into which the Thallogens are divided. There appear no traces of a terrestrial vegetation until we reach the uppermost beds of the Upper Silurian System. But, account for the fact as we may, it is at least worthy of notice, that, alike in the systems of our botanists and in the chronological arrangements of our geologists, the first or introductory class which occurs in the ascending order is this humble Thallogenic class. There is some trace in the Lower Silurians of Scotland of a vegetable structure which may have belonged to one of the humbler Endogens, of which, at least, a single genus, the Zosteraceæ, still exists in salt water; but the trace is faint and doubtful, and, even were it established, it would form merely a solitary exception to the general evidence that the first known period of vegetable existence was a period of Thallogens. The terrestrial remains of the Upper Silurians of England, the oldest yet known, consist chiefly of spore-like bodies, which belonged, says Dr. Hooker, to Lycopodiaceæ—an order of the second or acrogenic class. And, in the second great geologic period—that of the Old Red Sandstone—we find this second class not inadequately represented. In its lowest fossiliferous beds we detect a Lycopodite which not a little resembles one of the commonest of our club mosses—Lycopodium clavatum—with a minute fern and a large striated plant resembling a calamite, and evidently allied to an existing genus of Acrogens, the equisetaceæ. In the Middle Old Red Sandstone there also occurs a small fern, with some trace of a larger; and one of its best preserved vegetable organisms is a lepidodendron—an extinct ally of the Lycopodiums; while in the upper beds of the system, especially as developed in the south of Ireland, the noble fern known as Cyclopteris Hibernicus is very abundant. This fern has been detected also in the Upper Old Red of our own country, mingled with fragments of contemporary calamites. With, however, these earliest plants of the land yet known, there occurs a true wood, which belonged, as shown by its structure, to a gymnospermous or polycotyledonous tree, and which we find associated with remains of Coccosteus and Diplacanthus.

Fig. 2. CYCLOPTERIS HIBERNICUS. (Nat. size.)

Fig. 3. CONIFER OF THE LOWER OLD RED SANDSTONE. Cromarty. (Mag. forty diameters.)

And here let me remark, that the facts of Palæontological science compel us to blend, in some degree, with the classification of our modern botanists, that of the botanists of an earlier time. In a passage already quoted, Solomon is said to have discoursed of plants, "from the cedar tree that is in Lebanon, to the hyssop that springeth out of the wall,"—from the great tree to the minute herb; and Cowley rose, in his metrical treatise, as has been shown, from descriptions of herbs and flowers to descriptions of fruit and forest trees. And as in every age in which there existed a terrestrial vegetation there seem to have been "trees" as certainly as "herbs," the palæontological botantist finds that he has, in consequence, to range his classes, not in one series, but in two—the Gymnogens, or cone-bearing trees, in a line nearly parallel with the Acrogens, or flowerless, spore-bearing herbs. But the arrangement is in no degree the less striking from the circumstance that it is ranged, not in one, but in two lines. It is, however, an untoward arrangement for the purposes of the Lamarckian, whose peculiar hypothesis would imperatively demand, not a double, but a single column, in which the ferns and club mosses would stand far in advance, in point of time, of the Coniferæ. In the Coal Measures, so remarkable for the great luxuriance of their flora, both the Gymnogens and Acrogens are largely developed, with a very puzzling intermediate class, that, while they attained to the size of trees, like the former, retained in a remarkable degree, as in the Lepidodendra and the Calamites, the peculiar features of the latter. And with these there appear, though more sparingly, the Endogens—monocotyledonous plants, represented by a few palm-like trees (Palmacites), a few date-like fruits (Trigonocarpum), and a few grass-like herbs (Poacites). In the great Secondary division, the true dicotyledonous plants first appear; but, so far as is yet known, no dicotyledonous wood. In the earlier formations of the division a degree of doubt attaches to even the few leaves of this class hitherto detected; but in the Lower Cretaceous strata they become at once unequivocal in their character, and comparatively abundant, both as individuals and species; and in the Tertiary deposits they greatly outnumber all the humbler classes, and appear not only as herbs, but also as great trees. Not, however, until shortly before the introduction of man do some of their highest orders, such as the Rosaceæ, come upon the scene, as plants of that great garden—including the fields of the agriculturist—which it has been part of man's set task upon earth to keep and to dress. And such seems to be the order of classification in the vegetable kingdom, as developed in creation, and determined by the geologic periods.

Fig. 4.[5] THE GENEALOGY OF ANIMALS.

The parallelism which exists between the course of creation, as exhibited in the animal kingdom, and the classification of the greatest zoologist of modern times, is perhaps still more remarkable. Cuvier divides all animals into vertebrate and invertebrate; the invertebrates consisting, according to his arrangement, of three great divisions—mollusca, articulata, and radiata; and the vertebrates, of four great classes—the mammals, the birds, the reptiles, and the fishes. From the lowest zone at which organic remains occur, up till the higher beds of the Lower Silurian System, all the animal remains yet found belong to the invertebrate divisions. The numerous tables of stone which compose the leaves of this first and earliest of the geologic volumes correspond in their contents with that concluding volume of Cuvier's great work in which he deals with the mollusca, articulata, and radiata; with, however, this difference, that the three great divisions, instead of occurring in a continnous series, are ranged, like the terrestrial herbs and trees, in parallel columns. The chain of animal being on its first appearance is, if I may so express myself, a threefold chain;—a fact nicely correspondent with the further fact, that we cannot in the present creation range serially, as either higher or lower in the scale, at least two of these divisions—the mollusca and articulata. In one of the higher beds of the Upper Silurian System—a bed which borders on the base of the Old Red Sandstone—the vertebrates make their earliest appearance in their fourth or ichthyic class; and we find ourselves in that volume of the geologic record which corresponds to Cuvier's volume on the fishes. In the many-folded pages of the Old Red Sandstone, till we reach the highest and last, there occur the remains of no other vertebrates than those of this fourth class; but in its uppermost deposits there appear traces of the third or reptilian class; and in passing upwards still, through the Carboniferous, Permian, and Triassic Systems, we find reptiles continuing the master existences of the time. The geologic volume in which these great formations are included corresponds to the Cuvierian one devoted to the Reptilia. Early in the Oolitic System, birds, Cuvier's second class of the vertebrata, make their first appearance, though their remains, like those of birds in the present time, are rare and infrequent; and, for at least the earlier periods of their existence, we know that they were—that they haunted for food the waters of the period, and waded in their shallows—only from marks similar to those by which Crusoe became first aware of the visits paid to his island by his savage neighbors—their footprints, left impressed on the sands over which they stalked of old. This early Oolitic volume corresponds in its contents to the section devoted by Cuvier, in his great work, to his second class, the birds. And in the Stonisfield slate—a deposit interposed between the "Inferior" and "Great Oolites," we detect the earliest indications of his first or mammaliferous class, apparently represented, however, by but one order—the Marsupiata, or pouched animals, to whose special place in the scale I shall afterwards have occasion to refer. Not until we reach the times of the Tertiary division do the mammals in their higher orders appear. The great Tertiary volume corresponds to those volumes of Cuvier which treat of the placental animals that suckle their young. And finally—last born of creation—man appears upon the scene, in his several races and varieties; the sublime arch of animal being at length receives its keystone; and the finished work stands up complete, from foundation to pinnacle, at once an admirably adjusted occupant of space, and a wonderful monument of Divine arrangement and classification, as it exists in time. Save at two special points, to which I shall afterwards advert, the particular arrangement unfolded by geologic history is exactly that which the greatest and most philosophic of the naturalists had, just previous to its discovery, originated and adopted as most conformable to nature: the arrangements of geologic history as exhibited in time, if, commencing at the earliest ages, we pursue it downwards, is exactly that of the "Animal Kingdom" of Cuvier read backwards.

Let us then, in grappling with the vast multiplicity of our subject, attempt reducing and simplifying it by means of the classifying principle; not simply, however—again to recur to the remark of the metaphysician—as an internal principle given us by nature, but as an external principle exemplified by nature. Let us take the organisms of the old geologic periods in the order in which they occur in time; secure, as has been shown, that if our chronology be correct, our classification will, as a consequence, be good. It will be for the natural theologians of the coming age to show the bearing of this wonderful fact on the progress of man towards the just and the solid, and on the being and character of man's Creator—to establish, on the one hand, against the undue depreciators of intellect and its results, that in certain departments of mind, such as that which deals with the arrangement and development of the scheme of organic being, human thought is not profitlessly revolving in an idle circle, but progressing Godwards, and gradually unlocking the order of creation. And, on the other hand, it will be equally his proper business to demand of the Pantheist how—seeing that only persons (such as the Cuviers and Lindleys) could have wrought out for themselves the real arrangement of this scheme—how, I say, or on what principle, it is to be held that it was a scheme originated and established at the beginning, not by a personal, but by an impersonal God. But our present business is with the fact of the parallel arrangements, Divine and human—not with the inferences legitimately deducible from it.

Fig. 5. OLDHAMIA ANTIQUA;—the oldest known Zoophyte. Wrae Head, Ireland.

Fig. 6. PALÆOCHORDA MINOR. (One half nat. size.)

Beginning with the plants, let us, however, remark, that they do not precede in the order of their appearance the humbler animals. No more ancient organism than the Oldhamia of the Lowest Irish Silurians, a plant-like zoophyte somewhat resembling our modern sertularia, has yet been detected by the geologist; though only a few months ago the researches of Mr. Salter in the ancient rocks of the Longmynd, Shropshire, previously deemed unfossiliferous, have given, to it what seem to be contemporary vegetable organisms, in a few ill-preserved fucoids. So far as is yet known, plants and animals appear together. The long upward march of the animal kingdom takes its departure at its starting point from a thick forest of algæ. In Bohemia, in Norway, in Sweden, in the British Islands, in North America, wherever, in fine, what appears to be the lowest, or at least one of the lowest, zones of life has yet been detected, the rocks are found to be darkened by the remains of algæ, so abundantly developed in some cases, that they compose, as in the ancient Lower Silurians of Dumfriesshire, impure beds of anthracite several feet in thickness. Apparently, from the original looseness of their texture, the individual plants are but indifferently preserved; nor can we expect that organisms so ancient should exhibit any very close resemblance to the plants which darken the half-tide rocks and skerries of our coasts at the present time. We do detect, however, in some of these primordial fossils, at least a noticeable likeness to families familiar to the modern algæologist. The cord-like plant, Chorda filum, known to our children as "dead men's ropes," from its proving fatal at times to the too adventurous swimmer who gets entangled in its thick wreaths, had a Lower Silurian representative, known to the Palæontologist as the Palæochorda, or ancient chorda, which existed apparently in two species—a larger and smaller. The still better known Chondrus crispus, the Irish moss or carrageen of our cookery-books, has likewise its apparent though more distant representative in Chondritis, a Lower Silurian algæ, of which there seems to exist at least three species. The fucoids, or kelp weeds, appear to have had also their representatives in such plants as Fucoides gracilis of the Lower Silurians of the Malverns; in short, the Thallogens of the first ages of vegetable life seem to have resembled, in the group, and in at least their more prominent features, the algæ of the existing time. And with the first indications of land we pass direct from the Thallogens to the Acrogens—from the sea weeds to the fern allies. The Lycopodiaceæ;, or club mosses, bear in the axils of their leaves minute circular cases, which form the receptacles of their spore-like seeds. And when, high in the Upper Silurian System, and just when preparing to quit it for the Lower Old Red Sandstone, we detect our earliest terrestrial organisms, we find that they are composed exclusively of those little spore receptacles. The number of land plants gradually increases as we ascend into the overlying system. Still, however, the Flora of even the Old Red is but meagre and poor; and you will perhaps permit me to lighten this part of my subject, which threatens too palpably to partake of the poverty of that with which it deals, by a simple illustration.

Fig. 7. LYCOPODIUM CLAVATUM.

Fig. 8. EQUISETUM FLUVIATILE.

We stand, at low ebb, on the outer edge of one of those iron-bound shores of the Western Highlands, rich in forests of algæ, from which, not yet a generation bygone, our Celtic proprietors used to derive a larger portion of their revenues than from their fields and moors. Rock and skerry are brown with sea weed. The long cylindrical lines of Chorda filum, many feet in length, lie aslant in the tideway; long shaggy bunches of Fucus serratus and Fucus nodosus droop heavily from the rock sides; while the flatter ledges, that form the uneven floor upon which we tread, bristle thick with the stiff, cartilaginous, many-cleft fronds of at least two species of chondrus—the common carrageen, and the smaller species, C. Norvegicus. Now, in the thickly-spread fucoids of this Highland shore we have not a very inadequate representation of the first, or thallogenic vegetation—that of the great Silurian period, as exhibited in the rocks, from the base to nearly the top of the system. And should we add to the rocky tract, rich in fucoids, a submarine meadow of pale shell sand, covered by a deep green swathe of zostera, with its jointed saccharine roots and slim flowers, unfurnished with petals, we would render it perhaps more adequately representative still.

Fig. 9. OSMUNDA REGALIS. (Royal Fern.)

We cross the beach, and enter on a bare brown moor, comparatively fertile, however, in the club mosses. One of the largest and finest of the species, Lycopodium clavatum, with its long scaly stems and upright spikes of lighter green—altogether a graceful though flowerless plant, which the herd-boy learns to select from among its fellows, and to bind round his cap—goes trailing on the drier spots for many feet over the soil; while at the edge of trickling runnel or marshy hollow, a smaller and less hardy species, Lycopodium inundatum, takes its place. The marshes themselves bristle thick with the deep green horse tail, Equisetum fluviatile, with its fluted stem and verticillate series of linear brandies. Two other species of the same genus, Equisetum sylvaticum and Equisetum arvense, flourish on the drier parts of the moor, blent with two species of minute ferns, the moonwort and the adder's tongue—ferns that, like the magnificent royal fern (Osmunda regalis), though on a much humbler scale, bear their seed cases on independent stems, and were much sought after of old for imaginary virtues, which the modern schools of medicine refuse to recognize. Higher up the moor, ferns of ampler size occur, and what seems to be rushes, which bear atop conglobate panicles on their smooth leafless stems; but at its lower edge little else appears than the higher Acrogens—ferns and their allies. There occurs, however, just beyond the first group of club mosses—a remarkable exception in a solitary pine—the advance guard of one of the ancient forests of the country, which may be seen far in the background, clothing with its shaggy covering of deep green the lower hill-slopes. And as we found in the Thallogens of that littoral zone over which we have just passed, representatives of the marine flora of the Silurian System, from the first appearance of organisms in its nether beds, to its bone-bed of the Upper Ludlow rocks, in which the Lycopodites first appear, so in the Acrogens of that moor, with its solitary coniferous tree, we may recognize an equally striking representative of the terrestrial flora which existed during the deposition of these Ludlow rocks, and of the various formations of the Old Red Sandstone, Lower, Middle, and Upper.