SEM studies on vessels in ferns 8. Platyzoma

Using scanning electron microscopy (SEM), vessels are demonstrated for roots and rhizomes of Platyzoma microphyllum R.Br. Because vessels are not in simple linear series, but have tips in contact with tips of other vessels, vessel elements may have several end walls, and each of these can bear a perforation plate. Vessels in roots are narrow, but have wide perforations. In rhizomes, perforation plates have a wide range of morphology. The most notable of these involves displacement and, frequently, fusion of adjacent bars of secondary wall material, so that large perforations tend to alternate with narrow perforations or with two or three fused bars. Porose pit membranes are present in narrower perforations. The presence of wide perforations achieved by means of bar displacement characaterises not merely Platyzoma, but other ferns as well: Microgramma and Phlebodium. These three genera of ferns experience marked fluctuation in water availability, so that not only are vessels of potential value for rapid conduction during brief periods of water availability, but the presence of perforation plates conducive to such rapid conduction os of theoretical selective advantage as well. Stelar fibres that bear crystals on external surfaces of walls are reported for roots of Platyzoma. Such fibres have not been reported hitherto for ferns.