. Morphology of gymnosperms. Gymnosperms; Plant morphology. GNETALES 369 nificance. In Gnetum, as in Ephedra, the secondary wood contains true vessels associated with gymnospermous tracheids. The vascular anatomy of the group needs a wider range of investigation than has been given to it, and this has been partially supplied by a recent investigation by Hill and DeFradste (28). The traces entering the base of each coty- ledon are two in Ephedra, four (in two pairs) in Welimtschia, and four or five in Gnetum. The strands of the hypocotyl are inserted on the cotyle- donary strands, and are four
. Morphology of gymnosperms. Gymnosperms; Plant morphology. GNETALES 369 nificance. In Gnetum, as in Ephedra, the secondary wood contains true vessels associated with gymnospermous tracheids. The vascular anatomy of the group needs a wider range of investigation than has been given to it, and this has been partially supplied by a recent investigation by Hill and DeFradste (28). The traces entering the base of each coty- ledon are two in Ephedra, four (in two pairs) in Welimtschia, and four or five in Gnetum. The strands of the hypocotyl are inserted on the cotyle- donary strands, and are four in Ephedra, eight or less ih Welwitschia (quickly reduced to four), and a variable number (about 12-15) ^^ Gnetum. The transition to root structure occurs in the lower region of the hypocotyl, and in all cases the primary root is diarch. On the whole, the meager data available suggest a group. Figs. 410-412.—Welwitschia mirabilis: spicular cells from the perianth of the stami- nate flower; fig. 410, a branching cell, the branching represented in one plane; fig. 411, a simple cell; fig. 412, the cut end of a long cell, with lumen almost closed and the sur- face covered by crystals of calcium oxalate; X22S. farther removed from ferns than other groups of gymnosperms, and one that has developed more or less completely the true vessels characteristic of angiosperms. THE LEAF The opposite leaves of Ephedra, reduced to a two-toothed and scaly sheath, certainly suggest ancestors with true foliage leaves, and occasionally such leaves are developed now. The single pair of long-lived parallel-veined leaves of Welwitschia are remarkable. The stomata are in rows and deeply sunken, 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 Coulter, John Merle, 1851-1928; Chamberlain, Charles Joseph, b. 1863; Coulter, John Me
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