Myrothamnus flabellifolius Welw. is a desiccation-tolerant (' resurrection ') plant with a woody stem. Xylem vessels are narrow (14 µm mean diameter) and perforation plates are reticulate. This leads to specific and leaf specific hydraulic conductivities that are amongst the lowest recorded for angiosperms (k s 0n87 kg m −" MPa −" s −" ; k l 3n28i10 −& kg m −" MPa −" s −" , stem diameter 3 mm). Hydraulic conductivities decrease with increasing pressure gradient. Transpiration rates in well watered plants were moderate to low, generating xylem water potentials of k1 to k2 MPa. Acoustic emissions indicated extensive cavitation events that were initiated at xylem water potentials of k2 to k3 MPa. The desiccation-tolerant nature of the tissue permits this species to survive this interruption of the water supply. On rewatering the roots pressures that were developed were low (2n4 kPa). However capillary forces were demonstrated to be adequate to account for the refilling of xylem vessels and re-establishment of hydraulic continuity even when water was under a tension of k8 kPa. During dehydration and rehydration cycles stems showed considerable shrinking and swelling. Unusual knob-like structures of unknown chemical composition were observed on the outer surface of xylem vessels. These may be related to the ability of the stem to withstand the mechanical stresses associated with this shrinkage and swelling.# 1998 Annals of Botany Company
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