The occurrence and morphology of natural tyloses and gums in the vessels of 50 Japanese hardwoods (15 ring-, 34 diffuseand 1 radial-porous woods) were investigated using SEM. Tyloses were present exclusively or predominantly in 23 species (12 ring-, 10 diffuse- and 1 radial-porous woods) and gums in 15 species (3 ring- and 12 diffuse-porous woods). In the pore zones of most of the ringporous woods both tyloses and gums first occurred in an earlier ring number from the bark than in the diffNse- and radial-porous woods. Tyloses and gums originated from both ray and axial parenchyma cells in most species which have pit pairs connecting these cells to the vessels. Except for four species, the maximum and minimum diameters of the inner pit aperture from vessels to parenchyma cells were greater than 5 and 2 µm, respectively, in those species with tyloses, whereas the diameters were less than these values in species having gums. The forms of tylosis blockings in heartwood vessels were closely related to parenchyma patterns.