. Fossil plants : for students of botany and geology . Paleobotany. xxxn] VOLKELIA 209 black patches in fig. 461, A, in all probability represents the primary part of each stele to which the rest of the tissue has been added by the cambium. A striking feature of the secondary xylem is the absence of medullary rays: the tracheids resemble those of Cladoxylon and Protopitys in the transverse elongation of the pits (fig. 461, D) which form either a single row or several irregularly distributed rows. The primary xylem consists in the peripheral region of tracheids with very narrow scalariform pitt
. Fossil plants : for students of botany and geology . Paleobotany. xxxn] VOLKELIA 209 black patches in fig. 461, A, in all probability represents the primary part of each stele to which the rest of the tissue has been added by the cambium. A striking feature of the secondary xylem is the absence of medullary rays: the tracheids resemble those of Cladoxylon and Protopitys in the transverse elongation of the pits (fig. 461, D) which form either a single row or several irregularly distributed rows. The primary xylem consists in the peripheral region of tracheids with very narrow scalariform pitting which at first sight suggest close spiral bands (fig. 461, C),. Fig. 461. Volkelia refracta. A. Transverse section of a specimen in the Breslau Museum. B. Portion of a, stele; a, the crushed xylem on the outer side; 6, the inner side. C. Longitudinal section sMowing the median protoxylem. D. Tracheid from the secondary xylem. ^After Solms-Laubach.) while the inner tracheids are either annular or reticulate and associated with elongated parenchyma. The imperfectly preserved ground-tissue appears to consist of homogeneous parenchyma with radially disposed bands of stereome in the outer cortex. Our knowledge of Volkelia, though far from complete, justifies its generic separation from Cladoxylon from which it differs in the lack of medullary rays and in the structure of the primary portion of each stele. In the form and arrangement of the pits in the secondary tracheids Volkelia differs from Medullosa^aud s. Ill 14. 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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