. Fossil plants : for students of botany and geology . Paleobotany. ABC Pig. 140. Picea excelsa. Shoots of different ages showing changes in the appear- ance of the leaf-cushions: a leaf attached to a cushion in fig. A. (Slightly enlarged.) A portion of the cushion below the triangular leaf-scar often shows transverse gaping cracks or depressions (fig. 185, C) such as occur on a smaller scale on the older cushions of a Fir twig (fig. 140). Secondary thickening, as in recent trees, is not confined to the vascular cylinder but at an early stage, frequently before there are any signs of secondary

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. Fossil plants : for students of botany and geology . Paleobotany. ABC Pig. 140. Picea excelsa. Shoots of different ages showing changes in the appear- ance of the leaf-cushions: a leaf attached to a cushion in fig. A. (Slightly enlarged.) A portion of the cushion below the triangular leaf-scar often shows transverse gaping cracks or depressions (fig. 185, C) such as occur on a smaller scale on the older cushions of a Fir twig (fig. 140). Secondary thickening, as in recent trees, is not confined to the vascular cylinder but at an early stage, frequently before there are any signs of secondary wood, the outer region of the broad cortex becomes the seat of active cell-formation which results in the addition of a considerable thickness to the bark. At a later stage of increase in girth, the leaf-cushions are stretched. 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