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Page:Popular Science Monthly Volume 18.djvu/635

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A PIECE OF COAL.

amount of labor that can hardly be appreciated, but with results as certain as if the actual development had been watched in the living plant.

The plants, themselves, on which this old coal-producing fruit was borne, and whose carbonized stems and leaves lie heaped up and mingled with the spores, have some lessons of interest for the student of world-history. One of the best known of these plants has been called Lepidodendron, or scale-tree, on account of the beautiful scale-like markings impressed upon the bark (Figs. 1 and 2). These markings diamond-shaped and arranged in close-set spiral lines around the stem—are scars left by the falling leaves. Elaborately sculptured stems are found in all our coal-measures, often with dimensions indicating trees three to five feet in diameter, and seventy to a hundred feet in height. Such trees, judging from their abundance and world-wide distribution, must have been conspicuous objects in all the forest-covered swamps of the coal age. Conceive, if you can, of tall, rigid trunks, ornamented with delightful patterns of inimitable sculpture-work, rising to a height of thirty or forty feet and these dividing into two equal clumsy branches; then let each of these divide again and redivide until a number—though not a very great number—of smaller branches are produced; then clothe each of the branches with a bristling array of thick-set, lance-like leaves; let each branch terminate in a club-shaped cone or fruit from which multitudes of resinous-spores, at the proper seasons, came showering down, filling the air with clouds of dust for days and weeks together, and sifting in among the roots of all the dense undergrowth with which the coal-marsh is covered—and, having drawn this mental picture fairly, you will have some idea, perhaps, of a Lepidodendron (Fig. 3).

But, if we would award credit where credit is due, we must in all fairness acknowledge the preeminent importance of another group of

PSM V18 D635 Ideal section of a sigillaria stem.jpg
Fig. 9.—Ideal Section of a Sigillaria-Stem: a, pith; b, woody cylinder; c, inner bark; d, rind; e, bases of leaves; f, vascular thread running to the leaves; g, medullary rays.

plants to which we are indebted for by far the largest share of the coal. These plants outnumbered the Lepidodendrons in all the swamps; like Lepidodendrons, they rose to the dignity of great trees; the trunks were composed of firmer and more densely packed woody tissue; the bark was thick and rich in bituminous matter, and in some of them it