Abstract:Spiral thickenings in the yessels elements of 51 species belonging to 44 genera and 20 families chinese hardwoods were investigated by SEM and TEM.They were found in the vascular or vasicentric.Four types or spiral thickening were proposed,namely,brached,nonbrached,swirled and vestured;their forms,functions,distributions and origins were described in detail.Occurrence or non-occurrence and distribution of the spiral thickenings must be considered as a useful identification of hardwood.