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The morphology and structure of pollen grains are important for wind pollination and hence reproductive success in gymnosperms.To examine the role of pollen structures associated with pollination in Ginkgo biloba L, scanning electron and transmission electron microscopy was used to observe ultrastructure features of pollen.Compared with pollen grains before dispersal, spinules on the pollen surface disappeared, intine was thickened, and the cavities in the infratectum were smaller after pollen dispersal.However, after pollen hydration, spinules recovered on the pollen surface and the thickness of intine and size of cavities were similar to those of pollen before dispersal,suggesting that G.biloba pollen grains could adapt for dispersal in the air through changing their microstructure.In addition, high-resolution transmission electron microscopy revealed that calcium was mainly focused in the intine, revealing that the constitution of the intine and endexine could play an important role in pollen germination.Importantly, the use of both in vivo and in vitro pollen experiments revealed that the pollen grains dispersed, then hydrated and swelled on the surface of the pollination drop,this was accompanied by air bubble release and exposure of the germination area.The pollen of G.biloba sank down in the pollination drop, whereas saccate Cedrus deodara pollen always floated upwards through the pollination drop.These results indicated that the effectiveness of hydration and sinkability as a pollination mechanism is a result of its ability to efficiently exclude foreign pollen grains and preferentially concentrate pollen of G.biloba inside ovules.