Sem studies on vessels in ferns .3. Phlebodium and Polystichum

Scanning electron microscope (SEM) studies of xylem of roots and rhizomes of one species each of Phlebodium and Polystichum revealed the presence of vessels in both. Vessels in both, like those in Pteridium, have lateral perforation plates and end-wall perforation plates. Perforation plates on lateral walls feature smaller porosities than do the perforations on end walls. In Phlebodium, end-wall perforation plates retain pit membranes with porosities; end walls in Polystichum lack pit membrane remnants in most perforations. End-wall perforation plates are not uniform in either genus but vary with respect to differentiation from lateral-wall pitting, narrowness of bars, and presence of pit membrane remnants. Wide perforations alternating with narrow perforations characterize our material of Phlebodium. Rhizome transections show that tracheary elements in both genera tend to occur in large groupings in which each tracheary element tends to contact two to four other tracheary elements; this may correlate with perforations on lateral walls in addition to those on end walls. No tracheids were observed with certainty. Vessel presence in these two genera may be related to marked fluctuation in climatic regimes.