. Fossil plants : for students of botany and geology . Paleobotany. 76 PTEEIDOSPERMBAE [CH. with dark contents in the stem-tissues probably represent secretory- sacs. The leaf-traces on leaving the stele pursue a very gradually ascending course to the petiole; they retain their collateral structure in the pericycle and cortex and have no secondary xylem, but become concentric as they enter the base of a Fig. 412. Heterangium Grievii. Oblique longitudinal section of stele and part of cortex; p, pericycle. x 3. (Kidston CoU. 529.) Before passing to the description of the leaves, the more
. Fossil plants : for students of botany and geology . Paleobotany. 76 PTEEIDOSPERMBAE [CH. with dark contents in the stem-tissues probably represent secretory- sacs. The leaf-traces on leaving the stele pursue a very gradually ascending course to the petiole; they retain their collateral structure in the pericycle and cortex and have no secondary xylem, but become concentric as they enter the base of a Fig. 412. Heterangium Grievii. Oblique longitudinal section of stele and part of cortex; p, pericycle. x 3. (Kidston CoU. 529.) Before passing to the description of the leaves, the more striking features in the stem may be summarised with reference to the diagrammatic sketches shown in fig. 411. Fig. 411, A, represents a section of Heterangium Grievii approximately 2 cm. in its maximum diameter; at the periphery of the primary xylem, x^, and close to its outer margin are several protoxylem groups, not shown in the drawing, each of which marks the position of a mesarch trace. The zone of secondary xylem, x^, is interrupted by the exit of leaf-traces and one of these is seen at a in fig. 415, A, separated from the central primary xylem by a foliar gap filled with parenchyma. The pericycle is shown at p in fig. 412 and. 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
Size: 1271px × 1966px
Photo credit: © Central Historic Books / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, bookpublishercambr, bookyear1898
