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be rejected from the equation." True, but infinitely small quantities accumulating through infinite ages become finite, in fact, become very important; for it is these very same infinitely small residual quantities, rejected by astronomy as of no value, which, by their accumulation, constitute the progressive development of the earth and solar system. Without such small uncompensated forces history, whether geological, national, or individual, would be impossible. An insect philosopher, the span of whose life is a single day, attentively observing the daily cycle of the healthy human body, might rationally assert the stability of the human system. The body, at the end of twenty-four hours, has come back to the same spot whence it started. At least the variation, if any, must be infinitely small, and therefore, for all purposes of insect life, may be rejected as of no value. And yet it is the accumulation of this same infinitely small variation which constitutes the growth and progressive development of the body. This is not an exaggerated illustration, for 2,000 years, the whole age of astronomy, is but one day, yea, but a small fraction of a day, in the geological history of the earth.

I

The flora of the coal period is more complete than that of any previous or succeeding geological epoch. The whole number of fossil species of plants known is probably not far from 2,000. Of these, according to estimates made more than ten years ago, about 816 are from the "coal measures." The constant additions which have been made since that time, particularly by Dr. Newberry and others, from an examination of the coal fields of our own country, would probably bring the number up to at least 900. Probably, therefore, nearly if not quite one-half of all known fossil plants belong to this period. have already said that a coal seam is made up of the remains of such plants, yet it is not in the coal seams themselves that we find the best preserved specimens of coal plants. On the contrary, the vegetable matter is here so thoroughly disorganized that it is only by means of the microscope that we are able to detect its original structure. It is rather in the associated shale strata that the most beautiful impressions occur, particularly in the overlying black slate. Between the thin sheets of this slate the stems and leaves are as perfectly preserved, every vein and nerve, as between the leaves of the botanist's herbarium. This fact, viz: that the well-preserved plants are always found in abundance in this position, and never in the coal seam proper has, as it seems to me, an important bearing upon the theory of coal deposit. But of this we shall speak again in another place. You have here before you a magnificent slab of black slate, profusely covered with beautiful impressions of leaves and stems of ferns and calamites. In this case, as perhaps in most others, the impressions, though welldefined, are not conspicuous at a distance, because the color of the ground and of the figures are so nearly alike, but in some cases, when the shale background is light-colored, the relief of the coal-black impressions is very beautiful. The newly exposed roof of a coal mine has been compared by Dr. Buckland to the most magnificent fresco painted ceilings of Italian buildings.

But although the number of species of coal plants is so great, yet

coal is supposed to be composed principally of the remains of four families only, viz: Ferns, Sigillarice, Lepidodendrons, and Calamites. The abundance of individuals belonging to these families is so great, and their size so enormous, that they must have given character to the vegetation of this period, and may therefore be taken as representatives of its flora. As such, therefore, I shall consider them, and it will be our object in this lecture to give you some idea of their appearance and affinities.

There are certain periods in the history of our race upon which we are apt to gaze with peculiar interest and admiration-when the human mind, awakening from its sleep of barbarism, rejoices in the ostentatious display of its strength and its beauty, so in the history of our earth, the period of the coal stands out beyond all others as the "heroic age," when nature seemed to delight herself in the fantastic exercise of power, and to exhaust her strength in the production of vegetable giants and monsters. It will be my object to show that this age, although to the popular mind it may appear a mythological age, an age of wonders and prodigies, an age to which ordinary principles of reasoning are inapplicable; that this age is but one chapter, a page, in a connected history, one step in the accomplishment of the unvarying plans of Deity.

A glance at these drawings of coal plants will give you some general idea of the strange forms which constituted the flora of this period. But it is not only a vague general idea of external form which I wish to give you; we have already had too much of this in popular lectures on geology. If we would grasp the real thought expressed in the vegetation of this period; if we would understand the true significance of the coal flora in the Divine economy; if we would catch the keynote of this Divine harmony, we must take more than a superficial glance we must look deeply, thoughtfully, reverently. But, in order to make myself understood, I find it necessary to step a little out of the way, to give you a sketch of the great divisions of the vegetable kingdom and the characteristics of each, so that, by comparison, we may be able to determine the position of the coal plants. Whatever is noble and elevating in science must be equally interesting to every intelligent mind; but in order to appreciate it, it is absolutely necessary to master in some degree uninteresting technicalities. The jewel is inclosed always in an unattractive casket of lead; we must find the key before we can gain the prize.

The vegetable kingdom, then, is divided into two great classes: the Phænogams, or flowering plants, and the Cryptogams, or flowerless. The Cryptogams may be again divided into cellular and vascular Cryptogams. The cellular Cryptogams, such as the mosses, fungi lichens, sea weeds, &c., consist entirely of cellular tissue, while the vascular Cryptogams, such as ferns, club-mosses, equisetaceæ, (horse-tails,) combine the vascular tissue with the cellular. The Phonogams may also be divided into two sub-classes, viz: the Gymnosperms, or naked seeded plants, and the Angiosperms, or covered seeded plants. The Gymnosperms bear their seeds naked or exposed, either near the base of an open capillary leaf, as in the pine family, (Conifers,) fig. 12, or else

on its edges, as in the cycas family. Figs. 12 and 13 represent cross

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sections of the capillary leaves of naked seeded plants. The Angiosperms, on the contrary, bear their seeds enfolded within the capillary leaf or seed vessel, (figs. 14 and 15,) as in all the ordinary flowering plants. The Angiosperms are again subdivided into Monocotyledons, (one cotyledon or seed leaf in the embryo,) fig. 16, and Dicotyledons, (two seed leaves in the embryo,) fig. 17.

Fig. 17.

Dicotyledons,

Phænogams, Monocotyledons,

Angiosperms.

Conifers & Cycadæ, Gymnosperms.
Vascular Cryptogams.

Cryptogams, Cellular Cryptogams.

Now, the most important means of determining the families of coal plants are the internal structure of the stem and the venation of the leaves. Generally, indeed, these are the only means at our command. Let us inquire, then, how the great divisions of the vegetable kingdom are characterized in these respects.

Among Phænogams there are two very distinct types or plans of internal structure of the stem, viz: the Exogenous, or outside-growing, and the Endogenous, or inside-growing; the one represented by the hard-wood trees and shrubs, the other by the palms, canes, grasses, &c. On cross section of an exogen (fig. 18) we find three distinct zones of tissue. In the centre a zone of cellular tissue, the pith; exterior to this a zene of wood, and around this again a zone of cellular tissue, the bark. The zone of wood is, moreover, subdivided into concentric rings, which represent the annual layers of growth, and separated into wedges by radiating lines of cellular tissue (silver grain) connecting the cellular tissue of the pith with the cellular tissue of

Fig. 18.

Fig. 19.

the bark. In the Endogens, on the contrary, we have the woody tissue in the form of thread-like bundles, irregularly interspersed amongst the cellular. The dry stalk of an Indian corn is a familiar illustration of this structure. If such a stalk is broken across and the two parts carefully separated, the

thread-like bundles of woody and vascular tissue are observed to draw

out from the softer cellular tissue. Here we observe no distinct pith; on distinct bark separable from the wood; the wood not collected into a distinct zone; not arranged into concentric layers, nor divided by medullary rays. The exogenous plan of structure includes the Dicotyledons and the pine and cycas families; while endogen may be considered synonymous with monocotyledon.

In the vascular Cryptogams the woody and vascular tissue is still differently arranged. The stem of a club-moss, for instance, consists of a mass of cellular tissue inclosed in a rind of the same tissue more condensed, with a single central thread of vascular tissue. Sometimes there seems to be in the centre of this something like a very imperfect pith. The cellular Cryptogams, as their name indicates, consist entirely of cellular tissue.

Fig. 20.

It will be observed that, in the general structure and mode of growth, the family of pines (Gymnosperms) is allied to the highest order of plants, viz: the Dicotyledons, while in its reproduction it is below the Monocotyledons. This latter position is beyond doubt the true one; and a more attentive examination of the wood of pine in comparison with that of Dicotyledons will confirm us in this view. As this is a very important point, and as much false theorizing on the subject of the plants of the coal has been the result of a misconception of the true position of conifers, I will dwell a little more minutely than I should have otherwise considered it necessary to do. The wood of Dicotyledons consists of two distinct tissues, viz: the woody tissue proper and the vascular tissue. The woody tissue proper is composed of elongated cells, too small to be distinguished by the naked eye, while the vascular tissue is composed of very much larger cells or tubes. The visible pores in such wood as oak, chestnut, vine, &c., belong to this tissue. Fig. 20 represents cross section of two wooden wedges, with their medullary rays. The comparative size of the wood cells and the vessels is well shown. difference is often much greater than in the figure.

The

In pine wood, on the contrary, there is no distinction of woody and vascular tissue; but the so-called wood consists entirely of an open, thin-walled tissue, intermediate in every respect between the vascular and the woody layer and thinner walled than the true woody, but smaller than the true vascular. This is shown in the cross section, (fig. 21.) On a longitudinal section, (fig. 22,) the cells of pine wood are marked by large disc-like elliptical plates, which are entirely characteristic of this family. The smallest fragment is sufficient to distinguish it with the utmost certainty.

Now, if we trace the development of the tissues, either by passing from the lowest to the highest plants, or from the earliest embryonic to the mature condition of one of the higher plants, we shall find that all the different kinds of tissue are modifications of the cellular; that there is a more and more complete differentiation of form and special

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ization of function as development progresses. The longitudinal system is first formed by modification of the cellular, and then this is again differentiated into the two forms of woody and vascular tissue. Now, in the pine family, this last differentiation has not taken place. So far as its tissues are concerned, therefore, this family should rank below all other flowering plants.

Let us next examine the different classes of plants with respect to the venation of their leaves. With respect to their venation the leaves of plants are divided into three distinct kinds, viz: the reticulated, or netted veined, the parallel veined, and the dicholomously veined. In the first the veins branch and again run together, forming an inextricable net-work. (Fig. 23, a.) In the second the veins run parallel from one end of the leaf to the other, connected only by slender transverse bars, so that the leaf may be torn into

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d

a

Fig. 23.

b

parallel ribbons. (Fig. 23, b.) In the third the veins branch, but do not run together again. (Fig. 23, cand d.) The first is characteristic of the Dicotyledons; the second of the Monocotyledons; and the

third of the Ferns-perhaps of the vascular Cryptogams generally. The leaves of cellular Cryptogams are veinless. In this enumeration it will be observed I have not mentioned the Conifers. To which class, then, do the leaves of the pine family belong? Undoubtedly to the third. This fact cannot be easily demonstrated upon leaves of ordinary pines, for their cylindrical leaves show no veins, or, if visible, they seem to be parallel. But there are a few broadleaved Conifers, and these always show the dichotomous branching of the veins in the most unmistakable manner. In the Salisburia, for instance, we have as beautiful an instance of this mode of branching as can be found among the Ferns. The leaves of this Conifer are about two or three inches broad, the shape and venation very similar to that represented in Fig. 23, c, but much more beautiful. This close alliance in the venation of the leaves between the pines and the ferns is another evidence of the low position of the former among flowering plants. Thus it appears that this remarkable family of plants is allied to the highest Phænogams

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