RESISTANCE TO WATER-FLOW IN XYLEM VESSELS

Experimental data on flow resistances in xylem vessels with different lumen wall surface sculptures are presented. The technique involved using determinable forces at menisci to pull water through isolated undamaged metaxylem and protoxylem vessels which were empty but had water-saturated walls. In the horizontal orientation, the surface tension forces moved the water at velocities that the resisting viscous forces at the vessel walls would allow since inertial forces were found negligible. A high speed camera was used to determine the meniscus translation rates. Vessel diameters as well as average dimensions of the microscopic internal surface irregularities were measured with respect to axial position from the inlet. From these, flow resistances were determined in terms of dimensionless friction factor, f, as functions of Reynolds number, Re.It was found that, at certain helical ring thicknesses and spacing, resistance to flow was lowest. Deviations from these parameter values cause dramatic increases in resistance to flow. Results are applicable to normal flow in plants, i.e. without menisci present. © 1979 Oxford University Press.