. A manual of the North American gymnosperms [microform] : exclusive of the cycadales but together with certain exotic species. Bois; Trees; Gymnosperms; Gymnospermes; Arbres; Wood. ^ : iii i â 54 ANATOMY OF THE GYMNOSPERMS. The dark plates closely resemble Sanio's bands, for which they might very readily be mistaken upon casual observation, or they might likewise be mistaken for terminal and unpitted walls. In Dammara australis these features are presented in their typ- ical form. The transverse section shows such elements to be numerous and dis- posed in radial rows on each side of the medul
. A manual of the North American gymnosperms [microform] : exclusive of the cycadales but together with certain exotic species. Bois; Trees; Gymnosperms; Gymnospermes; Arbres; Wood. ^ : iii i â 54 ANATOMY OF THE GYMNOSPERMS. The dark plates closely resemble Sanio's bands, for which they might very readily be mistaken upon casual observation, or they might likewise be mistaken for terminal and unpitted walls. In Dammara australis these features are presented in their typ- ical form. The transverse section shows such elements to be numerous and dis- posed in radial rows on each side of the medullary ray (fig. 5). In a radial section they present the same fibrous and fusiform charac- ter as in A u- caria, but, in addition, the wall usually experi- ences a marked increase in sec- ondary growth within the region exactly opposite a ray (fig. 6). This fea- ture is also prominent in the transverse section (fig. 5). Such local increase in thickness always arises in adjacent cells in such a way that the more strongly thickened regions are exactly opposite, and they serve to constrict the cell cavity gradually from above and below, in such manner as to leave a channel about half the usual width of the cell cavity, which gradually widens upward and downward (fig. 6). It is at the position of maximum constriction that we find a transverse plate of variable thickness, but always of a reddish-brown color. These plates are always thinnest in their central region, and they may be of uniform thickness for the greater part of their extent. Fig. 4. Dammara austra- lis. Tangential section showing the relation of the resin plates and the medul- lary ray, and a fractured plate (). x 225. 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 Penhallow, D. P. (David Pearce), 1854-1910. Boston : Ginn & Co.
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