Fig. 12 Stigmaria rootlets springing from Sigillaria stem.
In the course of an extensive survey of the coal-field of South Wales, Mr. (now Sir William) Logan ascertained the important fact, that each coal-seam is underlaid by a bed of clay, in which the stems of stigmaria, branching freely in all directions, may be traced to the distance of many feet or even yards. They were recognised as undoubtedly occupying the site on which they grew, and consequently each coal-seam was held to rest upon an ancient soil. Some years afterwards, in making a cutting for the Lancaster and Bolton Railway, several upright massive stems belonging to a plant called sigillaria, were found to pass downwards into true stigmaria stems ([Fig. 12]). There could be no doubt that they were different parts of one and the same plant. This fact has since been abundantly demonstrated from the Nova Scotia coal-field. Many sigillariæ have been found there passing down into the fire-clay below, where they branch out horizontally as true stigmatiæ. It is evident, therefore, that the stigmaria was the under-ground portion of a plant, which, judging from the nature of the soil, and the free mode in which the tender rootlets branched off, appears to have lived in aquatic or marshy stations.
Fig. 13. Stigmaria.
The stigmaria is too well marked to be readily confounded with any other coal-measure plant. It had a rounded stem, seldom more than four or five inches across, which was marked by a series of circular tubercules with a puncture in the centre, arranged in spiral lines round the stem. Each of these tubercules is surrounded, in ordinary specimens, by a circular depression,[21] and the whole plant (if one may use the comparison) looks as if it had been smitten with small-pox. From the hollow in the centre of each protuberance, there shot out a long round rootlet, formerly thought to be a leaf, and since the tubercules are pretty thickly set, the stigmaria must have had a somewhat hirsute appearance as it crept through the mud. It would resemble a thick bearded stem of ivy, save that the fibres, instead of running up two sides, were clustered all round it. Along the centre of the root, there ran a woody pith of a harder and more enduring texture than the surrounding part of the plant. The space between the outer tuberculed rind and the inner pith, seems to have been of a soft cellular nature, and to have decayed first, for the pith is sometimes hollow, and may not unfrequently be seen at a distance from the centre, and almost at the outer bark—a circumstance that seems only explicable on the supposition, that while the surrounding portions were decaying, the firmer pith altered its position in the hollow stem, sinking to the lower side, if the plant lay prostrate, and that it did not itself begin to decay until the interior of the stem had been at least partially filled up with sand or mud, or fossilized by the infiltration of lime. From the root of the sigillaria, which has a curious cross-shaped mark on its base, the stems of stigmaria strike out horizontally, first as four great roots which subdivide as they proceed. Their subdivisions are dichotomous, each root splitting equally into two, and thus they want that intricate interlacing of rootlet which is so familiar to us. The whole disposition of these under-ground stems is singularly straight and regular, leading us to believe that they shot out freely through a soft muddy soil.
[21] Such is the usual aspect of the plant. But as the stems have been, for the most part, greatly flattened by the pressure of the superincumbent rocks, the sharpness of the pattern has been much effaced. In some specimens described by Dr. Hooker, as having been found in an upright position, the external ornamentation presents an appearance somewhat different. What in the common specimens stand out as tubercules, are there seen to be deep circular cavities, in which the shrunk flagon-shaped bases of the rootlets are still observable. (See above, [Fig. 13 b], which is taken from one of Dr. Hooker's plates. For a detailed description of the structure of stigmaria, see the paper above referred to in the Geological Survey Memoirs.) A very ornate species is mentioned by the late Hugh Miller, in which each tubercule formed the centre of a sculptured star, and the whole stem seemed covered over with flowers of the composite order. And what is, perhaps, still more curious, the stem was seen to end off 7 in an obtuse point, tuberculed like the rest of the plant.—Testimony of the Rocks, p. 461.
Some time ago I chanced to visit the remains of what had once been a royal residence, and still looked majestic even in decay. It gave a saddened pleasure to thread its winding stairs, and pass dreamily from chamber to hall, and chapel to closet; to stand in its gloomy kitchens, with their huge fire-places, whose blackened sides told of many a roaring fagot that had ruddied merry faces in days long gone by; to creep stealthily into the sombre dungeons, so dank, earthy, and cold, and then winding cautiously back, to emerge into the light of the summer sun. The silent quadrangle had its encircling walls pierced with many a window, some of which had once been richly carved; but their mullions were now sorely wasted, while others, with broken lintels and shattered walls above, seemed only waiting for another storm to hurl them among the roofless chambers below. In the centre of the court-yard stood a ruined fountain. It had been grotesquely ornamented with heads of lions and griffins, and was said to have once run red with wine. But it was silent enough now; the hand of time, and a still surer enemy, the hand of man, had done their worst upon it; its groined arches and foliaged buttresses were broken and gone, and now its shattered beauty stood in meet harmony with the desolation that reigned around. I employed myself for a while in looking over the fragments, marking now the head of some fierce hippogryph, anon the limbs of some mimic knight clad in armour of proof, and ere long I stumbled on a delicately sculptured fleur-de-lis, that might have surmounted the toilet-window of some fair one of old. Turning it over, I found its unhewn side exhibited a still more delicately sculptured stigmaria. The incident was certainly simple enough, perhaps even trifling. And yet, occurring in a spot that seemed consecrated to reverie, it awoke a train of pleasant reflection. How wide the interval of time which was bridged across in that sculptured stone! Its one side carried the mind back but a few generations, the other hurried the fancy away over ages and cycles far into the dim shadows of a past eternity. The one told of a land of flowers, musical with the hum of the bee and the chantings of birds, and gladdened by the presence of man; the other told of a land luxuriant, indeed, in strange forms of vegetation—huge club-mosses, tall calamites, and waving ferns—yet buried in a silence that was only broken fitfully by the breeze as it shook the spiky catkins or the giant fronds of the forest. The fleur-de-lis recalled memories of France—the sunny land of France—which stood out so brightly in the dreams of our school-days; the stigmaria conjured up visions of a land that was never gazed on by human eye, but rolled its rich champaign during the long ages of the Carboniferous era, and sometimes rises up dimly in the dreams of our maturer years. Between these two epochs how many centuries, how many cycles must have slowly rolled away! The fleur-de-lis was carved but yesterday; the stigmaria flourished when the earth was young, and had seen scarcely a third part of its known history.
I have said that the stem of the stigmaria is called sigillaria. The name may be translated signet-stem,[22] and has reference to one of the distinguishing peculiarities of the plant. About twenty British species are enumerated, some of them very dissimilar, yet they all agree in having long fluted stems with parallel rows of prominent seal-like tubercules. The sigillaria differed so widely in its whole contour and ornamentation from every living plant, that it is impossible to convey an idea of its form by reference to existing vegetation. Some of the species, as S. organum ([Fig. 14]), had their trunks traversed longitudinally by broad ridges separated by narrow furrows. Along the summit of each ridge there ran a line of tubercules, set regularly at distances varying from a third or a quarter of an inch to close contact. One may sometimes see no unfair representation of the bark of this ancient tree, when looking at a newly ploughed field in spring-time, having each of its broad ridges dotted with a row of potato sacks. Other species, while exhibiting the same plan, differed not a little in the details. In some the tubercules are round, in others angular, and in a third set double or kidney-shaped. In some they are far apart, in others they are strung together like a chain of beads. Sometimes they exist as mere specks, while occasionally they broaden out so as to equal in width the ridge that supports them. One species (S. reniformis), instead of the broad ridge and narrow furrow, exhibits an arrangement exactly the reverse. It looks not unlike a cast of the species first described, save that its broad flat furrows support rows of much larger tubercules. The breast of a lady's chemisette, with a thick-set row of buttons down each plait, would be somewhat like this species of sigillaria, with this difference, however, that the buttons on the plant were of a form that does not appear as yet to have come into fashion among the fair sex. Yet they had no little elegance, and like many other objects in the geological storehouse, might be a useful model for our students of design. They were neither round nor quite oval, but rather of a kidney-shape, or like a double cherry.
[22] The word sigillaria is really plural, and was used by the Romans to denote the little images which friends were wont to present to each other at the end of the Saturnalia. They answered pretty nearly to christmas-boxes and new year's gifts among ourselves. It is not uninteresting thus to find among the hard dry names of science, one that two thousand years ago was synonymous with all the kindliness of friendship.
