. Fossil plants : for students of botany and geology . Paleobotany. XXl] OSMUNDACEAE 333 petioles and the petioles of scale-leaves with an aborted lamina. A similar association of two forms of leaf is seen in the existing American species Osmunda Claytoniana and O.cinnamomea. The cortex and armour of leaf-bases are penetrated by numerous diarch roots. The xylem cylinder, six to seven tracheae broad, is characterised by the narrower diameter of its innermost ele- ments and—an important point—by the fact that the detachment of a leaf-trace does not break the continuity of the xylem cylinder (fig
![. Fossil plants : for students of botany and geology . Paleobotany. XXl] OSMUNDACEAE 333 petioles and the petioles of scale-leaves with an aborted lamina. A similar association of two forms of leaf is seen in the existing American species Osmunda Claytoniana and O.cinnamomea. The cortex and armour of leaf-bases are penetrated by numerous diarch roots. The xylem cylinder, six to seven tracheae broad, is characterised by the narrower diameter of its innermost ele- ments and—an important point—by the fact that the detachment of a leaf-trace does not break the continuity of the xylem cylinder (fig Stock Photo](https://c8.alamy.com/comp/PG15G7/fossil-plants-for-students-of-botany-and-geology-paleobotany-xxl-osmundaceae-333-petioles-and-the-petioles-of-scale-leaves-with-an-aborted-lamina-a-similar-association-of-two-forms-of-leaf-is-seen-in-the-existing-american-species-osmunda-claytoniana-and-ocinnamomea-the-cortex-and-armour-of-leaf-bases-are-penetrated-by-numerous-diarch-roots-the-xylem-cylinder-six-to-seven-tracheae-broad-is-characterised-by-the-narrower-diameter-of-its-innermost-ele-ments-andan-important-pointby-the-fact-that-the-detachment-of-a-leaf-trace-does-not-break-the-continuity-of-the-xylem-cylinder-fig-PG15G7.jpg)
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. Fossil plants : for students of botany and geology . Paleobotany. XXl] OSMUNDACEAE 333 petioles and the petioles of scale-leaves with an aborted lamina. A similar association of two forms of leaf is seen in the existing American species Osmunda Claytoniana and O.cinnamomea. The cortex and armour of leaf-bases are penetrated by numerous diarch roots. The xylem cylinder, six to seven tracheae broad, is characterised by the narrower diameter of its innermost ele- ments and—an important point—by the fact that the detachment of a leaf-trace does not break the continuity of the xylem cylinder (fig. 252). Each leaf-trace is at first elliptical in section; it then becomes curved inwards and gradually assumes the horse-shoe form as in Zalesskya and in the recent species. The single endarch protoxylem becomes subdivided until in the petiole it is represented by 20 or more strands.. 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 work.. Seward, A. C. (Albert Charles), 1863-1941. Cambridge : University Press