Abstract:The development of specific inclusion in the mesophyll cells of Ammopiptanthus mongolicus was observed by means of transmission electron microscopy. The inclusion is approximately oval-shaped with very high electron-density. It originates from outside of the central vacuole. During its early development it only contains small amount of vesicle-like elements and electron-dense materials. Then the two kinds of components gradually increase in amount and form a protuberance by endocytosis of the tonoplast. The protuberance becomes larger and larger, sometimes even occupies a great part of the vacuole. Later, the vesiclelike elements gradually decrease as the electron-dense materials rapidly increase, eventually filling up the protuberance. The protuberance gradually contracts and finally detaches from the tonoplast and immerses freely in the central vacuole. However, such inclusions were never found in small vacuoles. The inclusions usually appear in cold season and contain large quantity of lipid.