SEM STUDIES ON VESSELS IN FERNS .4. ASTROLEPIS

By means of scanning electron microscopy, the nature of vessels is des cribed for roots and rhizomes of Astrolepis sinuata (Lag. ex Swartz) D .M. Benham & Windham [= Notholaena sinuata (Lag. ex Swartz) Kaulf.], c ommonly placed in Pteridaceae. In both roots and rhizomes, end walls a re variously distinct from lateral walls; a few perforation plates are quite elongate with numerous bars, but most are of medium or short le ngth with fewer bars. Pit membrane remnants are generally sparse in th e perforation plates. Lateral wall perforation plates are present; som e may represent a multiplicity of facets at the tip of a tracheary ele ment. Lateral walls may have intact pit membranes or perforations. No tracheids were identified; apparently all tracheary elements are vesse l elements. The abundance of relatively short end walls with few bars on perforation plates may be correlated with rapid rates of water cond uction during the short growing season of this fern, which occupies ou tcrops in arid parts of the southwestern United States and Mexico.