If this be so, we ought to find the remains of organic structure in this region c. In fact, on referring to Fig. 7, which represents a tangential, longitudinal section of the same specimen, we perceive at ab a ligneous duct and some unchanged tracheæ situated in the carbonized region, and then at c the same elements, though flattened, in which, however, we still clearly distinguish the bands of the tracheæ; at d is found a trachea whose contents were already solidified, and which has not been flattened; then, near the surface, in the region, e, the pressure having been greater, it is no longer possible to recognize traces of organization in a tangential section. In a large number of cases, the fact that the coal does not seem to be organized must be due to the too great compression that the carbonized cells and vessels have undergone when yet soft and elastic, at the time this slow but continuous pressure was being exerted.
It also became of interest to find out whether, through the very fact of carbonization, the dimensions of the organic elements had perceptibly varied—a sort of research that presents certain difficulties. At present we have no living plant that is comparable, even remotely, with those that grew during the coal epoch. Moreover, the organic elements have absolutely nothing constant in their dimensions.
Still, if we limit ourselves to a comparison of the same carbonized wood, preserved on the one hand by petrifaction, and on the other hand non-mineralized, we find a very perceptible diminution in bulk. The elements have contracted in length, breadth, and thickness, but principally in the direction of the compression that they have undergone in the purely carbonized specimens.
In the vicinity of the carbonized portions, those of the tracheæ that have not done so have perceptibly preserved their primitive length, which has, so to speak, been maintained by their neighbors, but their other dimensions have become much smaller—a quarter in thickness and half in length.
FIG. 9.—Calamodendron, Commentry; prosenchymatous portion of the wood carbonized, X200.
If the two fragments of the same wood are, one of them silicified and the other simply carbonized and preserved in sandstone, the diminution in volume will have occurred in all directions in the latter of the two.
FIG. 10.—Calamodendron, fragment of the vascular portion of the wood carbonized.
Figs. 9 and 11, which represent a portion of the fibrous region of Calamodendron wood, may give an idea of the shrinkage that has taken place therein. In Figs. 11 and 12, which show a few tracheæ and medullary rays of the ligneous bands of the same plant, we observe the same phenomenon. We might cite a large number of analogous examples, but shall be content to give the following: Figs. 13 and 15 represent radial and tangential sections of the bark of Syringodendron pes-capræ. This is the first time that one has had before his eyes the anatomical structure of the bark of a Syringodendron, a plant which has not yet been found in a petrified state. It is coal, then, with its structure preserved, that allows of a verification of the theory advanced by several scientists that the often bulky trunks of Syringodendron are bases of Sigillariæ.