Presently there exist several methods to evaluate the pollenviability including viability stain and in vitro germination, amongwhich the in vitro germination method is thought to be more per-suasive (Galleta, 1983). A fixed so-called “optimal” condition isusually used in the determination and comparison of pollen viability. Through our experiments, we found in pecan the rehydrationcondition was one of the keys to understand the durable abilityof pollen germination. That is to say, pecan pollen actually doesn’tlose their viability rapidly but move to a different state in first sev-eral days. If we continue using the initial experimental condition