CARLQUIST, SHERWIN* and EDWARD SCHNEIDER. Santa Barbara Botanic Garden, 1212 Mission Canyon Road, Santa Barbara, CA 93105. - SEM studies of vessels in ferns of xeric habitats.
Vessels have hitherto been reported only in a few ferns
((Pteridium, Marsilea() on the basis of light microscopy. These
ferns occur in habitats markedly seasonal with respect to moisture
availability. Light microscopy cannot adequately resolve presence of
pit membranes in pits or perforation plates of vessels, but SEM
reveals pit membranes in vessels prepared by means of maceration and
sectioning. Care must be taken to identify any artifacts in membrane
absence, tearing, and distortion. Nevertheless, we can report with
certainty vessel elements in which end walls not only lack pit
membranes but have perforations different in size and shape from the
pits of lateral walls (Astrolepis, Dicranopteris, Microgramma,
Polystichum, Vittaria, Woodsia(). All of these experience
prolonged drought. In addition, other fern genera of dry habitats have
vessels with perforation plates morphologically like lateral wall
except that pit membrane remnants (often porose, weblike, or
vestigial) are present in perforations whereas nonperforated pit
membranes occur on lateral walls.
Key words: ferns, pit membrane, tracheids, vessels, xylem