. Fossil plants : for students of botany and geology . Paleobotany. xxxiv] PITYS 287 phloem, is raised by the fact that the primary strands are composed exclusively of xylem and are in most cases separated from the secondary wood by several parenchymatous cells. Scott favours the view that the primary phloem was originally at some distance from the primary xylem, the cambium being formed nearer to the phloem, an arrangement foreign to recent Gymnosperms. It is perhaps conceivable that the primary conducting strands included no true Fig. 487. Pitya antiqua. A, radial section of seconda
. Fossil plants : for students of botany and geology . Paleobotany. xxxiv] PITYS 287 phloem, is raised by the fact that the primary strands are composed exclusively of xylem and are in most cases separated from the secondary wood by several parenchymatous cells. Scott favours the view that the primary phloem was originally at some distance from the primary xylem, the cambium being formed nearer to the phloem, an arrangement foreign to recent Gymnosperms. It is perhaps conceivable that the primary conducting strands included no true Fig. 487. Pitya antiqua. A, radial section of secondary xyiem; B, transverse section showing the inner edge of the secondary wood and two primary-xylem strands with protoxylem, poc. (Kidston Coll.) The secondary xylem consists of tracheids with 4—5 alternate rows of hexagonal pits on the radial walls (fig. 487, A) and not infrequently on the tangential faces. Near the ends of the tracheids the pits are occasionally more scattered and separate and may be reduced to a single row^, but on the whole the pitting is essentially Araucarian. The medullary rays are generally 4 cells in breadth, but may be 7 cells broad. In depth the rays extend to 70 cells. As seen in fig. 487, B, the inner ends of the rays are especially broad owing to the tangential dilatation of the cells. The innermost secondary tracheids are characterised by pitting intermediate between spiral and reticulate. There are no regular rings of growth in the wood. Pitys frimaeva Witham. This species^, also founded on material from the Calciferous sandstone of Berwickshire, differs 1 Witham (33) A. PI. vin. fig. 2. 2 Ibid. p. 39, Pis. vm., xvi.; Scott (02) p. 335, Pis. ir., Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Seward, A. C. (Albert Charles), 1863-1941. Cambridge : University Press
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