Developmental and Structural Section
Carlquist, Sherwin , Schneider, Edward .
Tracheary elements in Ferns: new techniques, observations, and concepts.
LONGISECTIONS of xylem were studied with SEM for roots of Angiopteris, upright axes of Psilotum, and rhizomes of eight species of leptosporangiate ferns of diverse habits and varied ecological preferences. In contrast to earlier studies using macerations, razor-blade sections of fixed material from living plants were prepared. All materials studied showed porose or reticulate pit membranes present on presumptive end walls of tracheids. Contrasting non-porose pits were observed on lateral walls of some tracheids. Tracheid to parenchyma pit pairs may have porose pit membranes on the tracheid side, nonporose pit membranes on the parenchyma side, thus degree of porosity in a section can represent the degree to which one primary wall or the other is pared away. Reticulate pit membranes on tracheary element end walls are evidently widespread in fern. Such pit membranes may constitute an adaptation, different from coniferous tracheid bordered pit with its torus and margo, in which conduction is maximized concomitant with prevention of passage of air bubbles from one tracheid to another. Such cells should not be considered vessel elements, although the reticulate pit membranes suggest a degree of transition toward the membrane-free perforations of typical vessels. True vessels (pit membranes absent in perforations) do occur in ferns in roots of Astrolepis, Marsilea, Pteridium, and Woodsia. The preparation methods produced results freer from artifacts than did macerations, and interpretations must be altered accordingly. Reports of lateral, multiple, and interrupted perforation plants in ferns are probably the result of loss of pit membranes due to the oxidative action of maceration and should be rejected. Likewise, “pit dimorphism” (alternately wide and narrow pits) and “striate” (corrugated) pit membranes in ferns represent artifacts. True vessels in ferns probably always have secondary wall architecture of end walls different from that of lateral walls.
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1 - Santa Barbara Botanic Garden, 1212 Mission Canyon Road, Santa Barbara, California, 93105-2199, USA
xylem structure and function
Presentation Type: Oral Paper:Papers for Sections
Location: 312/Bell Memorial Union
Date: Monday, July 31st, 2006
Time: 2:00 PM