| Summary: | Transmission electron microscopy was conducted to characterize the mature pollen grains in the massulae of Habenaria sagittifera at anthesis to understand its ultramicroscopic features of mature pollen grains of this species. I found that (a) pollen walls on the surface of the massula consisted of several layers, which included the tectum, baculum, nexine-1, nexine-2, and intine, whereas pollen walls within the massula were comprised of less layers, lacking tectum and baculum; (b) both vegetative and generative nuclei in mature pollen grains were predominated by highly condensed chromatin, which occupied over half of the nuclear volume; and (c) the pollen grains did not contain lipid droplets, starch grains, or storage proteins, indicative of the absence of macromolecular storage reserves. In summary, the structural difference between walls on the surface of the massula and walls within the massula, the highly condensed status of the vegetative nucleus, and the absence of macromolecular storage reserves were the most noticeable ultramicroscopic characteristics of mature pollen grains of H. sagittifera.
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