The effects of temperature, water stress, hydration-dehydration cycles and seed priming on the germination of Callitris verrucosa and Callitris preissii, two Australian semi-arid coniferous tree species, were investigated. Optimum germination occurred at 18 degrees C, with a minimum germination time of 8-9 days for both species. At this temperature, germination was inhibited at osmotic potentials lower than - 1.0 MPa, but the capacity to germinate at low osmotic stress increased as the temperature decreased. Seed priming and hydration-dehydration cycles did not reduce seed viability, and Callitris seeds appear to retain the physiological changes induced by short-term hydration, as the time to the onset of germination was decreased to about 3 days. The capacity of Callitris seeds for incremental germination is likely to increase overall germination success in a low rainfall environment. (C) 1999 Academic Press.
