live in our forests, than these differ from the conifers of New Zealand or of New South Wales. We have thus, in the numerous ferns and numerous coniferous trees of the Coal Measures, known objects by which to conceive of some of the more prominent features of the flora of which they composed so large a part. We have not inadequate conceptions of at once the giants of its forests and the green swathe of its plains and hill-sides—of its mighty trees and its dwarf
underwood—of its cedars of Lebanon, so to speak, and its hyssop of the wall. But of an intermediate class we have no existing representatives; and in this class the fossil botanist finds puzzles and enigmas with which hitherto at least he has been able to deal with only indifferent success. There is a view, however, sufficiently simple, which may be found somewhat to lessen, if not altogether remove, the difficulty. Nature does not dwell willingly in mediocrity; and so in all ages she as certainly produced trees, or plants of tree-like proportions and bulk, as she did minute shrubs and herbs. In not a few of the existing orders and families, such as the Rosaceæ, the Leguminosæ, the Myrtaceæ, and many others, we have plants of all sizes, from the creeping herb, half hidden in the sward, to the stately tree. The wild dwarf strawberry and minute stone-bramble are of the same order as our finer orchard trees—apple, pear, and plum—or as those noble hawthorn, mountain ash, and wild cherry trees, that impart such beauty to our lawns and woods; and the minute spring vetch and everlasting pea are denizens of the same great family as the tall locust and rosewood trees, and the gorgeous laburnum. Did there exist no other plants than the Rosaceæ or the Leguminosæ, we would possess, notwithstanding, herbs, shrubs, and trees, just as we do now. And in plants of a greatly humbler order we have instances of similar variety in point of size. The humblest grass in our meadows belongs to the same natural order as the tall bamboo, that, shooting up its panicles amid the jungles of India to the height of sixty feet, looks down upon all the second class trees of the country. Again, the minute forked spleenwort of Arthur Seat, which rarely exceeds three inches in length, is of the same family as those tree-ferns of New Zealand and Tasmania that rise to an elevation of from twenty to thirty feet. And we know how in the ferns provision is made for the attainment and maintenance of the tree-like size and character. The rachis, which in the smaller species is either subterranean or runs along the ground, takes in the tree-fern a different direction, and, rising erect, climbs slowly upwards in the character of a trunk or stem, and sends out atop, year after year, a higher and yet higher coronal of fronds. And in order to impart the necessary strength to this trunk, and to enable it to war for ages with the elements, its mass of soft cellular tissue is strengthened all round by internal buttresses of dense vascular fibre, tough and elastic as the strongest woods. Now, not a few of the more anomalous forms of the Coal Measures seem to be simply fern allies of the types Lycopodiaceæ, Marsileaceæ, and Equisetum, that, escaping from the mediocrity of mere herbs, shot up into trees—some of them very great trees—and that had of necessity to be furnished with a tissue widely different from that of their minuter contemporaries and successors. It was of course an absolute mechanical necessity, that if they were to present, by being tall and large, a wide front to the tempest, they should also be comparatively solid and strong to resist it; but with this simple mechanical requirement there seems to have mingled a principle of a more occult character. The Gymnogens or conifers were the highest vegetable existences of the period—its true trees; and all the tree-like fern allies were strengthened to meet the necessities of their increased size, on, if I may so speak, a
coniferous principle. Tissue resembling that of their contemporary conifers imparted the necessary rigidity to their framework; nay, so strangely were they pervaded throughout by the coniferous characteristics, that it seems difficult to determine whether they really most resembled the acrogenous or gymnogenous families. The Lepidodendra—great plants of the club moss type, that rose from fifty to seventy feet in height—had well nigh as many points of resemblance to the coniferæ as to the Lycopodites. The Calamites—reed-like, jointed plants, that more nearly resemble the Equisetaceæ than aught else which now exists, but which attained, in the larger specimens, to the height of ordinary trees, also manifest very decidedly, in their internal structure, some of the characteristics of the conifers. It has been remarked by Lindley and Hutton of even Sphenophyllum—a genus of plants with verticillate leaves, of which at least six species occur in our Coal Measures, and which Brogniart refers to one of the humblest families of the fern allies—that it seems at least as nearly related to the Coniferæ as to its lowlier representatives, the Marsileaceæ. And it is this union of traits, pertaining to what are now widely separated orders, that imparts to not a few of the vegetables of the Coal Measures their singularly anomalous character.
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Fig. 21. EAST INDIA TREE-FERN.[7] (Asophila perrotetiana.)
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Fig. 22. SECTION OF STEM OF TREE-FERN.[8] (Cyathea.)
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| Fig. 23.
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Fig. 24.
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Fig. 25.
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LEPIDODENDRON STERNBERGII.[9]
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| Fig. 26. CALAMITES MOUGEOTII.
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Fig. 27. SPHENOPHYLLUM DENTATUM.
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Fig. 28. SIGILLARIA RENIFORMIS.
Let me attempt introducing you more intimately to one of those plants which present scarce any analogy with existing forms, and which must have imparted so strange a character and appearance to the flora of the Coal Measures. The Sigillaria formed a numerous genus of the Carboniferous period: no fewer than twenty-two different species have been enumerated in the British coal fields alone; and such was their individual abundance, that there are great seams of coal which seem to be almost entirely composed of their remains. At least the ancient soil on which these seams rest, and on which their materials appear to have been elaborated from the elements, is in many instances as thickly traversed by their underground stems as the soil occupied by our densest forests is traversed by the tangled roots of the trees by which it is covered; and we often find associated with them in these cases the remains of no other plant. The Sigillaria were remarkable for their beautifully sculptured stems, various in their pattern, according to their species. All were fluted vertically, somewhat like columns of the Grecian Doric; and each flute or channel had its line of sculpture running adown its centre. In one species (S. flexuosa) the sculpture consists of round knobs, surrounded by single rings, like the heads of the bolts of the ship carpenter; in another (S. reniformis) the knobs are double, and of an oval form, somewhat resembling pairs of kidneys—a resemblance to which the species owes its name. In another species (S. catenulata) what seems a minute chain of distinctly formed elliptical links drops down the middle of each flute; in yet another (S. oculata) the carvings are of an oval form, and, bearing each a round impression in its centre, they somewhat resemble rows of staring goggle-eyes; while the carvings in yet another species (S. pachyderma) consist chiefly of crescent-shaped depressions. The roots, or rather underground stems, of this curious genus attracted notice, from their singularity, long ere their connection with the carved and fluted stems had been determined, and have been often described as the "stigmaria" of the fossil botanist. They, too, have their curious carvings, consisting of deeply marked stigmata, quincuncially arranged, with each a little ring at its bottom,
