1. Vessel-length distribution in stems of some American woody plants. Can. J. Bot. 59: 1882-1892. Vessel-length distributions in some trees, shrubs, and a vine have been calculated from measurements of particle penetration and of air-volume flow through the xylem. In shrubs and diffuse-porous species, longest vessels were about 1 m long, but most of them were much shorter, the largest percentage in the 0-10 cm length class. In the two ring-porous species investigated (Quercus rubra and Fraxinus americana), the longest vessels often were as long as the tree's stem, but most of them were much shorter. In the grapevine (Vitis labrusca) which has large-diameter vessels (ca. 30Q km) a small percentage of the vessels was 8 m, but most of them were less than 5 m long. In a given species, lengths of the longest vessel were quite variable, but the distribution of the short lengths was more constant. In general, vessel lengths are correlated with vessel diameters: wide vessels are longer. Even in diffuse-porous species, the slightly narrower latewood vessels are somewhat shorter than the wider earlywood vessels. The method is a simplified version of that described by Skene and Balodis, but using a programmable desk calculator. It works best with diffuse-porous species in which vessels are randomly distributed in the stem, and less well in species with wide vessels, because as vessels reach the length of the stem itself, they cannot be randomly distributed.

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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,/, 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.

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