Nuclear behaviour is studied inAcacia auriculiformis A. Cann. with reference to aging in both axial and ray parenchyma cells (contiguous to vessels and away from the vessels). The size of the nucleus and nucleolus reduces gradually towards the inner sapwood and at last they disappear at the heartwood boundary. Nuclei show lobing, fissuring, fragmentation and contraction in this zone prior to their disintegration. Thus a gradual loss of vitality of parenchyma cells during aging is noted. The parenchyma cells contiguous to vessels seem to be more actively involved in formation of heartwood extractives.