SEM Studies on Vessels in Ferns. 5. Woodsia scopulina

Scanning electron microscopy (SEM) studies of macerations reveal that vessels are present in both roots and rhizomes of Woodsia scopulina. In rhizomes, there is less differentiation between lateral walls and end walls. In both root and rhizome vessels, there are perforation plates both on end walls and on lateral walls; because of the grouping of tracheary elements, more than one cell facet at a cell tip can qualify as an end wall. Lateral wall perforation plates are less specialized than end wall perforation plates. Lateral wall perforations often have porose pit membranes, whereas end wall perforations often lack pit membrane remnants, especially in roots. Tracheids may be present in addition to vessels, but because one cannot see all facets of a cell and many cells are broken or overlain, absence of perforation plates on all tracheary elements cannot be established with certainty. Woodsia obtusa has less specialized vessels: end wall perforation plates have porose pit membranes, and lateral perforation plates are apparently lacking. Greater specialization of vessels characterizes adaptation to more seasonal habitats in angiosperms; this correlation appears to apply to ferns as well. Woodsia scopulina tends to occupy sites of higher latitude or altitude than those of W. obtusa.