Abstract: The hybrids failed to get when crossing P.tricuspidata with P.quinquefolia.Germination of pollen and growth of pollen tube were studied by fluorescence microscope observation.The findings are as follows:pollens of P.tricuspidata and P.quinquefolia could germinate on the surface of their stigmas,respectively.Pollen tubes could grow into styles.While crossing P.tricuspidata with P.quinquefolia,most of the pollens could not germinate on the stigma.Even if germinated,the pollen tubes showed some abnormity such as twinning,tip inflation and bursting.2～48 h after pollinating,pollen tube was not observed in the styles of mother parents.It can be concluded that the cross-incompatibility was taken place on the surface of stigma.