Abstract: Transmission electron microscopic observations on the mesophyll cells of Ammopiptanthus mongolicus showed that in winter time, there was a kind of electron dense structure widely distributed in cytoplasm. This kind of structure mainly located around the chloroplasts which had generally been disintegrated and had many osmiophilic globuli. Some of this structure even pasted with chloroplast envelope membranes, and few existed in well developed chloroplasts and vacuoles. The structures were different in size, usually ellipsoidal shaped or semicircular shaped. The surface of the structures did not possess a layer surround membrane and vesicular shaped structures, but a few of radiate protuberances. The structures were very dark in electron dense and their staining was quite even. The formation of a great quantity of the structures may be related with increasing coldness resistance of plants.

Key words: Ammopiptanthus mongolicus, Mesophyll cell, Cytoplasm, Chloroplast, Electron dense structure, community structure, target tree tending, species composition, natural secondary shrubs, species diversity, closed forest management