. Morphology of gymnosperms. Gymnosperms; Plant morphology. 8 MORPHOLOGY OF GYMNOSPERMS aquilina (fig. 5), the figure referred to showing nine smaller peripheral vascular strands and four much larger central ones. It has been shown (31) that the young stem of Pteris is not polys telle, but that the vascular cylinder is an amphiphloic siphonostele, like that of Adian- tum. In growing to the adult stage it passes gradually into the poly-. FlG. 5.—Pteris aquilina: transversesectidnof stem, showing the polystele; Xio.— After Coulter (88). stelic condition by the overlapping of elongated leaf gaps
. Morphology of gymnosperms. Gymnosperms; Plant morphology. 8 MORPHOLOGY OF GYMNOSPERMS aquilina (fig. 5), the figure referred to showing nine smaller peripheral vascular strands and four much larger central ones. It has been shown (31) that the young stem of Pteris is not polys telle, but that the vascular cylinder is an amphiphloic siphonostele, like that of Adian- tum. In growing to the adult stage it passes gradually into the poly-. FlG. 5.—Pteris aquilina: transversesectidnof stem, showing the polystele; Xio.— After Coulter (88). stelic condition by the overlapping of elongated leaf gaps (see below), and also by the passing of peripheral vascular strands into the pith. It is evident that the various types of stele are not restricted to different groups of ferns, but may be found as the adult condition at all levels. For example, in existing gymnosperms the .ectophloic siphonostele, made up of collateral bundles, is the characteristic type of cylinder. Whether this was attained by way of the polystelic condition, as has been suggested (36), or directly from a siphonostehc condition, may not be clear; in any event, it would seem to be the most advanced type of cylinder, but it is found at various levels among. 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 Coulter, John Merle, 1851-1928; Chamberlain, Charles Joseph, b. 1863; Coulter, John Merle, 1851-1928. Morphology of spermatophytes. Part I. Gymnosperms. Chicago, University of Chicago Press
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