The leaf-traces, where they traverse the cortex, have the structure of the foliar bundles in Cycads, for they are of the collateral type, and their xylem is mesarch, the spiral elements lying in the interior of the ligneous strand.
A point of anatomical interest is the occurrence in the vascular bundles of the cotyledons, scale-leaves, and elsewhere of a few centripetally developed tracheids, which give to the xylem-strands a mesarch structure such as characterizes the foliar bundles of cycads.
The attachment of the branches was immediately above the node, and usually between two foliar traces, as in the recent genus.
This is the first indication of a conducting foliar strand or leaf bundle and forms an approach to leptom, though it is not so specialized as the leptom of the higher Phaeophyceae.
In leaves in which no sheath is produced we not infrequently find small foliar organs, stipules, at the base of the petiole (fig.
These are with few exceptions foliar structures, known in comparative morphology as sporophylls, because they bear the spores, namely, the microspores or pollen-grains which are developed in the microsporangia or pollen-sacs, and the megaspore, which is contained in the ovule or megasporangium.