The tissue water relationships of Callitris columellaris, Eucalyptus melliodora and Eucalyptus microcarpa investigated using the pressure-volume technique.

Using the pressure-bomb to construct pressure-volume curves, a cellular basis of differential drought resistance was found between Callitris columellaris (F. Muell), Eucalyptus melliodora A. Cunn. ex Schauer, and Eucalyptus microcarpa Maiden. Between these three species differences were found in bound water, relative water content and water potential at zero turgor, osmotic potential at full turgor and bulk modulus of elasticity. It is suggested that these parameters showed C. columellaris to be the most, and E. melliodora the least drought resistant of the three species.Preliminary studies also showed that drought hardening may involve an increase in bound water content, dry weight: turgid weight ratio and a decrease in osmotic potential at full turgor and water potential at zero turgor.