SEM studies on vessels in ferns. 11. Ophioglossum

With scanning electron microscopy (SEM), the nature of metaxylem vessel ele ments and tracheids was examined in Ophioglossum crotalophoroides, O. pendu lum subsp. falcatum, and O. vulgatum roots and rhizomes. Vessels were ident ified in all species. End walls of vessel elements, which bear perforations , are like lateral wall pitting of those elements in the secondary wall fra mework and differ only in absence of pit membranes or presence of pit membr ane remnants. Some of the perforations contain pit membrane remnants that h ave large pores, small porosities, or are threadlike or weblike in structur e. Dimorphic perforations were found in some vessel elements of rhizomes of O. pendulum subsp, falcatum. Tracheids are very likely present in addition to vessels in all three species. The secondary wall framework of both trac heids and vessels is basically scalariform, although deviations in pattern are present. Vessel elements of Ophiglossum are entirely comparable to thos e of leptosporangiate ferns. (C) 1999 The Linnean Society of London.