Fig. 9.

In planta hydraulic pressure pulses. Pressure variations in the upper and lower regions of poplar stems (Populus alba×tremula L. hybrid) when bending occurs in between those two regions. The pressure increase was very fast and the recovery lasted a few seconds. The magnitude of the signal increased with the magnitude of the mechanical strain, that is inversely to the curvature. Radius of curvature was 700mm (A), 500mm (B), and 300mm (C). Bending speed was constant. Permanent differences between upper and lower pressure corresponded to the hydrostatic pressure of the water column between the two sensors 0.9 m apart. (This figure is available in colour at JXB online.)