including the การคืนสภาพcondition to test pollen viability, the germination result is much worse than the real value. And this alsoreminds us of cautious using of in vitro germination method tocompare pollen viability. In plants, it has proved that controlledrehydration allows the phospholipids in the plasma membranebilayer to go through phase transition before being exposed to bulkwater (Crowe et al., 1989). Thus the change of rehydration condi-tion probably suggest the transition of physiological state of plasmamembrane which is the mechanism of early change of pollen via-bility.