Fig 4. The SEM observation of pollen germination and pollen tube growth in different cross combinations among single-petal (SP), double-petal (DP) and multi-petal (MP) jasmine plants.

(a) At 1 h after pollination (HAP), in SP × DP (pollen receptor × pollen donor), the pollen tube had just emerged from the germinal aperture. (b) At 2 HAP, in SP × DP, the pollen tube had penetrated into the stigma. (c) At 2 HAP, in DP × MP, the pollen tube had penetrated into the stigma. (d) At 8 HAP, in SP × DP, the number of geminated pollen grains (arrow heads) reached the peak. (e) At 8 HAP, in DP × SP, the number of geminated pollen grains (arrow heads) reached the peak. (f) In MP × DP, the number of geminated pollen grains (arrow heads) reached the peak at 12 HAP. (g) In SP × DP, a circulated and twisted pollen tube on the stigmatic surface at 12 HAP. (h) In MP × SP, a collapsed pollen tube on the stigma at 12 HAP. (i) In SP × MP, a pollen tube enlarged abnormally just after emerging from the aperture at 12 HAP. Abbreviations: PG, pollen grain; PT, pollen tube; St, stigma