ANEUROPHYTALEAN PROGYMNOSPERMS FROM THE MIDDLE DEVONIAN MILLBORO SHALE OF SOUTHWESTERN VIRGINIA.
University of MICHIGAN, 1985 - 194 pages
The documentation of protoxylem patterns in aneurophytes, in conjunction with evidence from Psilophyton dawsonii (Banks, Leclercq, and Hueber 1975) suggests that the transition from the haplostelic condition to the ribbed, protostelic condition resulted from: (1) regularization of the branching pattern to produce a one-third 'phyllotactic' fraction; and (2) closer vertical spacing of lateral appendages along the axis. These changes would result in vertically superposed, fused appendage traces arranged
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