SEM Studies on Vessels in Ferns. 4. Astrolepis

Abstract

-By means of scanning electron microscopy, the nature of vessels is described for roots and rhizomes of Astrolepis sinuata (Lag. ex Swartz) D.M. Benham & Windham [= Notholaena sinuata (Lag. ex Swartz) Kaulf.], commonly placed in Pteridaceae. In both roots and rhizomes, walls are variously distinct from lateral walls; a few perforation are quite elongate with numerous bars, but most are of medium or short length with fewer bars. Pit membrane remnants are generally sparse in the perforation plates. Lateral wall perforation are present; some may represent a multiplicity of facets at the tip of a tracheary element. Lateral walls may have intact pit membranes or perforations. No tracheids were identified; apparently all tracheary elements are vessel elements. The abundance of relatively short walls with few bars on perforation may be correlated with rapid rates of water conduction during the short growing season of this fern, which occupies outcrops in arid parts of the southwestern United States and Mexico. Scanning electron microscopy (SEM) offers a highly effective method of demonstrating the presence of vessels, because with this method pores large enough to constitute perforations can be seen. We have been attempting to describe the nature and extent of vessels in ferns by means of SEM (Carlquist et al., 1997; Carlquist and Schneider, in press; Schneider and Carlquist, 1997. Our studies have taken as a point of departure the studies of White (1962, 1963), in which walls appreciably different from lateral walls were recorded in tracheary elements of particular ferns. White (1962) suspected that some of these tracheary elements might be vessels. Astrolepis sinuata was a species for which White (1962) figured tracheary elements that have end plates different in their patterns from lateral wall pitting. Light microscopy cannot reveal presence of pores in pit membranes of ferns, and thus White's conclusions on vessel presence on the basis of light microscopy were speculative except where clear presence of vessels is concerned. White (1961, 1962) accepted the presence of vessels in Pteridium and Marsilea. Because of the inability of light microscopy to resolve perforations, earlier literature has reports that vessels are present in some ferns other than Pteridium (GwynneVaughan, 1908); these reports were contradicted by Bancroft (1911) and Duerden (1940). In extending White's observations, we can confirm that there are clear instances of vessels in which scalariform perforation lacking any vestiges of pit membranes are present. Some of the vessels of Pteridium conform to this pattern (Carlquist & Schneider, in press), although some vessels in that species retain pit membranes that are porose; these porosities qualify such tracheary elements as vessels. In some ferns, only porose pit membranes occur on walls; this is true of Woodsia obtusa (Sprengel) Torrey (Carlquist et al., 1997). Perforations of this sort on lateral walls of vessels were reported in This content downloaded from 157.55.39.123 on Fri, 20 May 2016 09:41:13 UTC All use subject to http://about.jstor.org/terms AMERICAN FERN JOURNAL: VOLUME 87 NUMBER 2 (1997) rI C^ ' -^Bsi ^ 7-