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 characterises 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 is 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.