Coal; its history and uses . be held answerable for the way in whichthe abridgment is executed. 76 COAL. CHAP. III. hence the name; most authors now assign them to thehorse-tails or Equisetaceae. When Calamites were iirst described and figured, thefurrows and constricted nodes were supposed to charac-terise the outer surface of the plant, the tapering endwas very naturally regarded as the growing point, andthe circle of scars adjacent to every node was taken toindicate the attachment of a whorl of leaves to the these suppositions prove to be incorrect. It is onlyin our own day, and by
Coal; its history and uses . be held answerable for the way in whichthe abridgment is executed. 76 COAL. CHAP. III. hence the name; most authors now assign them to thehorse-tails or Equisetaceae. When Calamites were iirst described and figured, thefurrows and constricted nodes were supposed to charac-terise the outer surface of the plant, the tapering endwas very naturally regarded as the growing point, andthe circle of scars adjacent to every node was taken toindicate the attachment of a whorl of leaves to the these suppositions prove to be incorrect. It is onlyin our own day, and by the patient labour of many workers,that the most fundamental questions of structure havebeen satisfactorily answered. Well preserved stems, im-bedded, not in sandstone, but in ironstone or calcareousnodules, have been sliced by the lapidarys wheel, andfrom the careful study of hundreds of these sections, ageneral conception of the organisation of the plant, accu-rate and useful, though far from complete, has Fig. 5. Restoration of part of stem of young Calamite, showing a nodeand portions of two internodes. From Williamson (Phil. Trans. , pt. 2, 1871). Let us first examine the structure of a single inter-node. Each contains a number of vertical radiatingwedges, separated by corresponding plates of pith-likecellular tissue. The wedges consist of bundles of longvessels intermixed with cellular tissue after a fashion CUA1-. 111. COAL PLANTS. 77 which will be immediately described. The entire massof wedges forms what is known, as the woody zone, butit should be remarked that the common form of wood-cells, met with in our forest-trees, has not been found inany Calamite. If it be now supposed that the hollow cylinder justdescribed as the woody zone is invested by a bark andlined by a thin layer of central pith, while the verticalradiating plates of cellular tissue (the primary medullaryrays of Prof. Williamson), which separate the woodywedges, are continuou
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