SEM studies of vessels in ferns 14. Ceratopteris

SEM study of xylem macerations of Ceratopteris thalictroides (L.) Brongn. ( Parkeriaceae, or Pteridaceae, tribe Ceratopterideae) has co-occurring vesse l elements and tracheids in rhizormes and probably also in roots, a conditi on newly reported for ferns. Vessel elements with helical thickening in the root have perforation plates that consist of elliptical holes in primary w alls, with no thinning or discontinuation of the gyres of secondary wall ba nds; groups of perforations alternate with smaller zones of intact primary wall. Perforations of this type are not visible with a light microscope, an d thus the perforation plates differ from those previously figured for vasc ular plants [Bailey, I.W., 1944. Am. J. Pot. 31, 421-428] in which helical elements have perforation plates in which the bands show alterations with r elation to the perforation plates. End wall facets of rhizome vessels that are perforation plates, have the same morphology as lateral walls; some per foration plates also occur on lateral walls. Weblike pit membranes that con tain pores of various sizes are present on some perforation plates and in t he transitions between perforation plates and intact lateral wall pitting. The presence of clearly differentiated vessels in Ceratopteris shows that v essels are present even in a submersed aquatic fern. The xylem of Ceratopte ris opens new questions about co-occurrence of vessel elements and tracheid s in ferns, relative morphology, distribution, and abundance of the two cel l types, and functional and evolutionary significance of vessel element pre sence in a fern that has maximal moisture availability. (C)2000 Elsevier Sc ience B.V All rights reserved.