. Fossil plants : for students of botany and geology . Paleobotany. XXXVIII] COLYMBBTES 493 into the next, a curving of the elements is frequently evident, and m a few cases it is quite possible to trace a single radial series of tracheids through an angle of 90° running in the same section, first as a transverse and then as a vertical series. One and the same medullary ray also can sometimes be followed, first in trans- verse and then in radial longitudinal section, which later again turns to true transverse. The inference is therefore drawn that there was but a single cambium, which had peri
. Fossil plants : for students of botany and geology . Paleobotany. XXXVIII] COLYMBBTES 493 into the next, a curving of the elements is frequently evident, and m a few cases it is quite possible to trace a single radial series of tracheids through an angle of 90° running in the same section, first as a transverse and then as a vertical series. One and the same medullary ray also can sometimes be followed, first in trans- verse and then in radial longitudinal section, which later again turns to true transverse. The inference is therefore drawn that there was but a single cambium, which had periodic changes of. p. pm. b X, y, X, y, x^ y^ x^ y^ Xs" Fia. 581. Colymbetes Edwardsi. Diagram of stem in transverse (A) and radial longitudinal (B) section, p, pith; pm, perimeduUary xylem; b, bays of first, vertically running, secondary xylem; x^.x^, etc., zones of horizontally running secondary xylem cut transversely in the radial and radially in the transverse section of the stem; y^, y^, etc., longitudinally running xylem cut transversely in the transverse and longitudinally in the radial section. (After Stopes.) direction.' Leaf-traces (fig. 580, It) are large and numerous; they are spirally disposed and pass nearly straight through successive xylem-zones: each trace consists of a small-celled groimd-tissue including stone-cells and patches of tracheids in more or less regular radial rows. Tangential sections of the wood show that the tracheids follow a sinuous course forming loops enclosing numerous medullary rays. As the pith and xylem are the only tissues preserved it is on their structure that any speculation as to afiinity must be based. The close arrangement of the leaf-traces (about 1 cm. apart), as. 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. C
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