PLANTS OF THE COAL. 3^9 



like a Corinthian column, and ornamented with seal-like impressions in 

 vertical ranks, representing the phyllotaxis ; unbranched or else divid- 

 ing only into a few large branches, clothed 

 thickly with long, stirlish, tapering leaves. 

 From the base of the trunk extended large, 

 radiating roots, branching dichotomously and 

 sparsely, with many long, thread-like root- 

 lets penetrating the soil below. The stumps 

 of Sigillaria and Lepidodendrons, with these 

 large, horizontally-spreading roots and thread- 

 like appendages, are very common in the 

 under-clay, and were long supposed to be a 

 peculiar plant, and called Stigmaria, on ac- 

 count of the round Spots {stigma) On their Fig. 504.— Stigmaria ficoides (after 



surface (Fig. 504). They are now known to e * quer 



belong to Sigillarids and Lepidodendrids, and are either roots or spread- 

 ing rhizomes (underground branches). 



In the following figure (505), taken from Dawson, we have at- 

 tempted to realize the general appearance of a Sigillaria. Their trunks 

 were sometimes of prodigious length and diameter. They were prob- 

 ably the largest trees of the time. In a coal-seam in Dauphin County, 

 Pennsylvania, flattened stems were found four feet and even five feet 

 in width. Some of these were exposed for fifty feet, with but little 

 apparent diminution. One was exposed sixty-five feet, and was esti- 

 mated to have extended at least thirty feet more. Another was exposed 

 seventy feet, and was estimated to have been eighty to one hundred 

 feet when growing.* 



The Sigillarids are regarded as closely allied to the Lepidodendrids. 

 Indeed, the two families shade into each other in such wise that there 

 are many genera the position of which, whether in the one family or in 

 the other, is doubtful. The typical Sigillaria, however, differs in gen- 

 eral port from the typical Lepidodendron, chiefly in possessing a more 

 Palm-like, or Cycas-like, or Dracena-like stem. They are evidently, 

 like the Lepidodendrids, closely allied to Lycopods, but their alliance 

 with higher classes is even stronger than that of Lepidodendrids. 



The internal structure of the stem entirely confirms this conclusion. 

 A cross-section (Fig. 506) of a Sigillaria-stem shows a hard external 

 rind, d, inclosing a great mass of loose, cellular tissue (inner bark), 

 c c, through the center of which runs a comparatively small woody 

 cylinder, b b, and in the center of this again a large pith, a a. From 

 the woody cylinder go bundles of fibro- vascular tissue,//, through the 

 cellular tissue of the inner bark, to the leaves, e e. Thus far the de- 



* Taylor, Statistics of Coal, pp. 149, 150; Williamson, Nature, vol. viii, p. 447. 

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