Germination behavior of pollen grains on the stigma 4 h after pollination in Nelumbo nucifera. (A, B) Many pollen grains germinated on the stigma in GA. ( C, D) pollen tubes penetrated the stigma and grew through the transmitting tissues of the style. (E-H) Some pollen grains germinated on the stigma in MQ, but callose was deposited in the pollen tubes or the pollen tubes were ruptured. Thus the pollen tubes failed to penetrate the stigma. C, Callose; Cp, callose plug; Pc, Papilla cell; Pg, pollen grain; Pt, pollen tube.