. The anatomy of woody plants. Botany -- Anatomy. GNETALES 369 The anatomy of the Gnetales is of particular importance at the present time when they have come to the front once more, either as a cognate stock with the dicotyledons or as their actual ancestors. The study of the internal organization of the group in comparison with the dicotyledonous angiosperms reveals many features of marked resemblance. Both are provided with large rays which are clearly fusion products; and in both the wood shows conducting elements belonging to the category of vessels. The rays apparently supply a very coge
. The anatomy of woody plants. Botany -- Anatomy. GNETALES 369 The anatomy of the Gnetales is of particular importance at the present time when they have come to the front once more, either as a cognate stock with the dicotyledons or as their actual ancestors. The study of the internal organization of the group in comparison with the dicotyledonous angiosperms reveals many features of marked resemblance. Both are provided with large rays which are clearly fusion products; and in both the wood shows conducting elements belonging to the category of vessels. The rays apparently supply a very cogent argu- ment for the close affinity of the Gnetales and the angiosperms. I n the case of the vascular struc- tures, however, it is not so clear that a morphological identity of the ele- ments present in the two groups can be successfully maintained. In the dicotyledons the pits present on the terminal walls of the vascular elements are not larger than those which appear laterally, and the perforation of the vessel takes place as the result of fusions of opposite pits, as has been shown in an earlier chapter. A very different situation manifests itself, as indicated above, in the genera of the Gnetales. Here the vascular elements have exceedingly large pits on their terminal walls, and in Ephedra these are usually without membranes,. FIG. 265.—Transverse section of a leaf bundle in Welwitschia 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 Jeffrey, Edward C. (Edward Charles), b. 1866. Chicago, Ill. , The University of Chicago Press
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