XVI International Botanical Congess

In our survey of macerated xylem of nearly all major families of ferns (including Psilotaceae), we have found vessels in all genera studied except Botrychium (Ophioglossaceae), all others have vessels, may have some tracheids in both roots and rhizomes, Ceratopteris has both vessels and tracheids. The paucity of prior reports of vessels in ferns derives from transparency of pit membranes as seen with light microscopy. Ferns from habitats with greater moisture fluctuation have large perforations (alternating with narrow pits). Specialized perforation plates relate to ecology rather than to phylogenetic position. All monocots studied have vessels in both roots and stems and as in ferns, have porose pit membranes at ends of perforation plates.