Water Flow in Vessels with Simple or Compound Perforation Plates

Hydraulic conductance of vessels was studied in young stem internodesand petioles of five species of dicotyledons that have simpleor compound perforation plates. Measured conductances of Clematisdioscoreifolia, Hardenbergia violacea, and Olea europaea, whichhave simple perforation plates, ranged from 92 to 106% of predictedvalues based on Hagen-Poiseuille flow through ideal capillaries.Petioles of Liquidambar styraciflua and Liriodendron tulipifera,which have compound perforation plates, had measured hydraulicconductances in spring-collected material that matched predictedconductances, but values averaged 60% of predicted in materialfrom late summer, suggesting blockage of vessels with time.An analog model of a vessel with and without compound perforationplates was developed from tygon tubing and steel pins to determinethe effect of obstruction by bars, which produced little flowreduction. Likewise, calculations based on the observed geometryof a scalariform perforation plate suggested that the platetypically reduced flow by only 1%. These data suggest that flowrates in vessels with simple as well as compound perforationplates are essentially equal to flows in ideal capillaries ofthe appropriate diameters. Clematis dioscoreifolia, Hagen-Poiseuille, Hardenbergia violacea, hydraulic conductance, Liquidambar styraciflua, Liriodendron tulipifera, Olea europaea, xylem