SEM studies on vessels in ferns - 8. Platyzoma

Using scanning electron microscopy (SEM), vessels are demonstrated for root s and rhizomes of Platyzoma microphyllum R.Br. Because vessels are not in s imple linear series, but have tips in contact with tips of other vessels, v essel elements may have several end walls, and each of these can bear a per foration plate. Vessels in roots are narrow, but have wide perforations. In rhizomes, perforation plates have a wide range of morphology. The most not able of these involves displacement and, frequently, fusion of adjacent bar s of secondary wall material, so that large perforations tend to alternate with narrow perforations or with two or three fused bars. Porose pit membra nes 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 o f water availability, but the presence of perforation plates conducive to s uch rapid conduction is of theoretical selective advantage as well. Stelar fibres that bear crystals on external surfaces of walls are reported for ro ots of Platyzoma. Such fibres have not been reported hitherto for ferns.