Open main menu

Page:Popular Science Monthly Volume 18.djvu/636

This page has been validated.

seems probable that large nut-like fruits were produced in place of spores. They are known as Sigillarias, and differ from Lepidodendrons, in addition to the characters already enumerated, in having stems loss frequently branched; the stems are also longitudinally fluted like some great columns of architectural beauty and finish, and between each pair of vertical ribs are now found the leaf-scars in variable but always orderly arrangement (Figs. 4, 5, 6). Instead of at the ends of the branches, the fruit was borne in cones, resembling pine-cones, springing from the sides of the stem. The leaf-scars often resemble impressions made upon wax by the old-fashioned seal, and hence the name Sigillaria, or seal-tree. Great, somber, stiff, post-like things they must have been, as, crowding each other in all the swamps, they lifted to the sky their great, bald trunks, with scarcely any branches, and nothing worthy of the name of foliage. Perhaps we should say that the most important part of Sigillaria was really underground, for all the old coal-swamps seem to have been traversed in every direction with a perfect network of creeping subterranean or subaqueous stems, and from these arose the aërial fruiting stems that we have called Sigillaria. Such underground stems, creeping and interlacing through the peat-like humus, must have formed a much-needed foundation on which to support the tangled forest of vegetation that grew and accumulated in all the quaking, boggy marshes. These creeping stems are called Stigmaria, and were known for a long time as one of the most abundant fossils of the coal, before their relation to Sigillaria was so much as suspected. They have markings arranged something as in Lepidodendron, but when we find them undisturbed—still imbedded by the old soil in which they grew—there arise from the center of the several scars long, thread-like filaments now known as rootlets (Fig. 7).

Almost every seam of coal has been shown to rest on a bed of clay, called among miners the under-clay or dirt-bed. This clay is penetrated in every direction by fossil roots with upright stumps sometimes attached, and it requires no argument to show that it is an old fossil forest bed—the original soil in which some, at least, of the coal-plants rooted and grew. This old soil has always been known to be particularly rich in Stigmariæ with the thread-like rootlets still in place, but it was not until Mr. Binney and others discovered Sigillarian stumps arising from wide-spreading Stigmarian roots that the real relations of the two forms of vegetation were perceived and acknowledged. It is always easy to do a thing after we have been shown how, and so nothing is more common now in all the coal measures, both of Europe and America, than to find the upright stumps and the subterranean stems still maintaining their original relative positions.

Such, in some particulars, were the Lepidodendrons and Sigillarias of the coal age. The two groups of plants differ widely in some respects, but they are connected by a complete series of intergrading