Resistances to fluid flow of model xylem vessels with simple and scalariform perforation plates

but they are ineYcient at transmitting water, both because they have narrow lumens and because water can only The resistances of xylem vessel walls and perforation pass between them through the primary cell wall. Xylem plates has been investigated using 18 large-scale vessel elements, meanwhile, have evolved from tracheids physical models made of plastic tubing into which through widening of the lumen, shortening of the cell, scale models of plates were inserted. Flow of water and partial loss of the end walls ( Frost, 1930a). Together, through vessels was modelled using glycerol instead these changes have reduced the flow resistance of xylem of water to keep the Reynolds number below 0.1. The vessels, allowing them to conduct water more eYciently technique proved easy, cheap and reliable. up the plant. Results showed that perforation plate resistance is Wider cells are more eYcient because the resistance of low compared with the resistance of the walls, what- a cylindrical vessel is inversely proportional to the fourth ever the plate morphology; plates only provided power of its radius. Resistance, R, is given by the Hagen0.6‐18.6% extra resistance. Simple plates provided Poiseuille equation ( Vogel, 1994) less resistance than scalariform plates, but because they are arranged closer together in vessels, resistance values (1.7‐5.1%) overlap with those of scalari