| Abstract: | Metasequoia is endemic to China. Present study deals with ultrastructure of pollen exine of M. glyptostroboides Hu et Cheng, and in comparision with other genera of the family. Pollen grains of Metasequoia are spheroidal or subsphoroidal and 27.8(24.3–32.3) μm in diameter. There is a papilla in the distal face. The papilla is wide at the base, 3.5–5.2 μm high, with pointed and circular end and the base crooked toward one side. Exine is about L5 μm thick, layers distinct, Nexine is as thick as sexine. Surface weakly granulate. According to observation by SEM, exine is covered with fine granules and rather coarse tuberculae. The former can be easily separated from the latter. The loose and uneven tuberculae are provided with minute spinules on the surface and generally fall off after acetolysis. The fine and dense granulae, however, remain intact after acetolysis. The study by TEM shows that ektexine is made of granules densely arranged and connected with each other. In addition, sparse Ubisch bodies are unevenly distributed on granular layer with geminate surface. The thick endexine, is composed of 10–15 lamellae. It is worthy to note that all lamellae possess tripartite structure. But lamellae of endexine in other genera of Taxodiaceae have no tripartite structure except the lamella near ektexine. Number of lamella and thickness of endexine in Metasequoia differ from those of other genera in Taxodiaceae; for example endexine with 8–10 lamellae in Taxodium, 8–9 lamellae in Sequoia, 6–7 lamellae in Glyptostrobus, 6–8 lamellae in Cunninghamia, about 16 lamellae in Cryptomeria etc. |
