“Here, however, an objection may be made to me, drawn from the physiological value of the vertebræ, the function of which, as is well known, is, on the one hand, to furnish a solid support to the muscular contractions which determine the movements of the trunk, and, on the other, to protect the centres of the nervous system, by forming a more or less solid case completely around them. The bodies of the vertebræ are particularly destined to the first of these offices; the neurapophyses to the second. What can be more natural than to admit, from the consideration of this, that in the head, the bodies of the vertebræ diminish in proportion as the moving function becomes lost, while the neurapophyses are considerably developed for protecting the brain, the volume of which is very considerable, when compared with that of the spinal marrow? Have we not an example of this fact in the vertebræ of the tail, where the neurapophyses become completely obliterated, and a simple cylindrical body alone remains? Now, may it not be the case, that in the head, the bodies of the vertebræ have disappeared; and that, in consequence, there is a prolongation of the cord only as far as the moving functions of the vertebræ extend? There is some truth in this argument, and it would be difficult to refute it a priori. But it loses all its force the moment that we enter upon a detailed examination of the bones of the head. Thus, what would we call, according to this hypothesis, the principal sphenoid, the great wings of the sphenoid, and the ethmoid, which form the floor of the cerebral cavity? It may be said they are apophyses. But the apophyses protect the nervous centres only on the side and above. It may be said that they are the bodies of the vertebræ. But they are formed without the concurrence of the dorsal cord; they cannot, therefore, be the bodies of the vertebræ. It must therefore be allowed, that these bones at least do not enter into the vertebral type; that they are in some measure peculiar. And if this be the case with them, why may not the other protective plates be equally independent of the vertebral type; the more so, because the relations of the frontals and parietals vary so much, that it would be almost impossible to assign to them a constant place?”
[32] It is stated by Mr. Witham, that, “except in a few instances, he had ineffectually tried, with the aid of the microscope, to obtain some insight into the structure of coal. Owing,” he adds, “to its great opacity, which is probably due to mechanical pressure, the action of chemical affinity, and the percolation of acidulous waters, all traces of organization appear to have been obliterated.” I have heard the late Mr. Sanderson, who prepared for Mr. Witham most of the specimens figured in his well-known work on the “Internal Structure of Fossil Vegetables,” and from whom the materials of his statement on this point seem to have been derived, make a similar remark. It was rare, he said, to find a bit of coal that exhibited the organic structure. The case, however, is far otherwise; and the ingenious mechanic and his employer were misled, simply by the circumstance, that it is rare to find pieces of coal which exhibit the ligneous fibre, existing in a state of keeping solid enough to stand the grinding of the lapidary’s wheel. The lignite usually occurs in thin layers of a substance resembling soft charcoal, at which, from the loose adhesion of the fibres, the coal splits at a stroke; and as it cannot be prepared as a transparency, it is best examined by a Stanhope lens. It will be found, tried in this manner, that so far is vegetable fibre from being of rare occurrence in coal,—our Scotch coal at least,—that almost every cubic inch contains its hundreds, nay, its thousands, of cells.
[33] On a point of such importance I find it necessary to strengthen my testimony by auxiliary evidence. The following is the judgment, on this ancient petrifaction, of Mr. Nicol of Edinburgh,—confessedly one of our highest living authorities in that division of fossil botany which takes cognizance of the internal structure of lignites, and decides, from their anatomy, their race and family:—
“Edinburgh, 19th July, 1845.
“Dear Sir,—I have examined the structure of the fossil wood which you found in the Old Red Sandstone at Cromarty, and have no hesitation in stating, that the reticulated texture of the transverse sections, though somewhat compressed, clearly indicates a coniferous origin; but as there is not the slightest trace of a disc to be seen in the longitudinal sections parallel to the medullary rays, it is impossible to say whether it belongs to the Pine or Araucarian division. I am, &c.,
“William Nicol.”
It will be seen that Mr. Nicol failed to detect what I now deem the discs of this conifer,—those stippled markings to which I have referred, and which the engraver has indicated in no exaggerated style, in one of the longitudinal sections (b) of the wood-cut given above. But even were this portion of the evidence wholly wanting, we would be left in doubt, in consequence, not whether the Old Red lignite formed part of a true gymnospermous tree, but whether that tree is now represented by the pines of Europe and America, or by the araucarians of Chili and New Zealand. Were I to risk an opinion in a department not particularly my province it would be in favor of an araucarian relationship.
[34] The following digest from Professor Balfour’s very admirable “Manual of Botany,” of what is held on this curious subject, may be not unacceptable to the reader. “It is an interesting question to determine the mode in which the various species and tribes of plants were originally scattered over the globe. Various hypotheses have been advanced on the subject. Linnæus entertained the opinion that there was at first only one primitive centre of vegetation, from which plants were distributed over the globe. Some, avoiding all discussions and difficulties, suppose that plants were produced at first in the localities where they are now seen vegetating. Others think that each species of plant originated in, and was diffused from, a single primitive centre; and that there were numerous such centres situated in different parts of the world, each centre being the seat of a particular number of species. They thus admit great vegetable migrations, similar to those of the human races. Those who adopt the latter view recognize in the distribution of plants some of the last revolutions of our planet, and the action of numerous and varied forces, which impede or favor the dissemination of vegetables in the present day. They endeavor to ascertain the primitive flora of countries, and to trace the vegetable migrations which have taken place. Daubeny says, that analogy favors the supposition that each species of plant was originally formed in some particular locality, whence it spread itself gradually over a certain area, rather than that the earth was at once, by the fiat of the Almighty, covered with vegetation in the manner we at present behold it. The human race rose from a single pair; and the distribution of plants and animals over a certain definite area would seem to imply that the same was the general law. Analogy would lead us to believe that the extension of species over the earth originally took place on the same plan on which it is conducted at present, when a new island starts up in the midst of the ocean, produced either by a coral reef or a volcano. In these cases the whole surface is not at once overspread with plants, but a gradual progress of vegetation is traced from the accidental introduction of a single seed, perhaps, of each species, wafted by winds or floated by currents. The remarkable limitation of certain species to single spots on the globe seems to favor the supposition of specific centres.”
[35] Rhodomenia palmata and Alaria esculenta.
[36] Porphyra laciniata, Chorda filum, and Enteromorpha compressa.