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Science 23 December 2005:
Vol. 310. no. 5756, p. 1924
DOI: 10.1126/science.1120479
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Brevia

Torus-Margo Pits Help Conifers Compete with Angiosperms

Jarmila Pittermann, John S. Sperry*, Uwe G. Hacke, James K. Wheeler and Elzard H. Sikkema

Department of Biology, University of Utah, 257S 1400E, Salt Lake City, UT 84112, USA.


Fig. 1. (A) Sapwood-area resistivity versus average conduit diameter for conifer tracheids with torus-margo (+TM) pit membranes and for angiosperm vessels with homogenous pit membranes. Crosses are tracheids substituted with angiosperm pit resistance (–TM). (B) Average conduit length versus diameter. Crosses show the tracheid length required to compensate for the substitution of angiosperm pits. (C) Flow resistance through pits on a membrane-area basis versus cavitation pressure. (D) Scanning electron microscope image of pit membranes with secondary wall removed. (Left) Torus-margo membrane of conifer tracheids; (right) homogenous pit membrane of angiosperm vessels (3). (E) Schematic side view of conducting pits. (F) Conduit network with pits conducting water and sealed against air entry. (G) Side view of pits in sealed and air-seeding position. Air leakage nucleates cavitation in the xylem sap. [View Larger Version of this Image (68K GIF file)]
 

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Science. ISSN 0036-8075 (print), 1095-9203 (online)