| Abstract: | The pollen strobilus Cordaianthus concinnus is examined as a possible indicator of the basic pattern of vascular architecture in stems of the Cordaitales. Bract traces arise from two points in the stele of the bilateral primary axis and diverge to the regularly arranged, four-ranked bracts. Tracheids to the axillary secondary shoots arise as two traces that flank the position of bract trace emission. Distally, the secondary shoot traces unite to form a stele that becomes increasingly dissected at successively higher levels. Although radially aligned, these tracheids show thickening patterns on all walls and are not separated by vascular rays; they are therefore interpreted as primary xylem. The traces form sympodia that are similar to those of typical eustelic gymnosperms. Scale traces from the secondary shoots arise by the tangential division of an individual axial bundle and occur in arrangements that range from a ½ to a % spiral. The vascular architecture of these secondary axes is interpreted as the equivalent of that in the stems of extant conifers with spiral phyllotaxis. |
