Abstract: Structures of secondary xylem of wild and cultivated Pinus pumila (Pall.) Regel have been observed under light microscope, polarized microscope and scanning electron microscope. The growth rings of the trunk and branches exhibit an eccentric growth, while the distinction between sap- and heart-wood is relatively obvious. Spiral checks and trabeculae are present in tracheids. The intercellular spaces among tracheids are distinct. Ray-tra-cheids are located at the margin of the rays, some low rays consist only of ray-tracheids. Rays are uniseriate and fusiform, within the latter the transverse resin ducts present. The number of the longitudinal resin ducts shows a negative correlation with the width of the growth rings. The pits in the cross-field are window-like. The dwarf Pinus pumila shows some characteristics of the compression wood.

Key words: Pinus pumila, Secondary xylem, Dwarf