Formation of the graft-union was observed for cleft grafts of 'Fuyu' on 'Kluai Rusi' rootstock. The stages in formation of the union were as follows: (1) Pre-callus, where 2 days after grafting only a wound periderm with red material were observed. (2) Callus, formation was found 2-10 days after grafting. (3) Cambium bridge, formation of new cambium in the callus produced by stock while no cambial formation in the scion side. The new cambium initiation on scion side appeared and completely connected with stock cambium at 12 days after grafting. (4) After 14 days of grafting, the new cambium layer differentiated into new vascular tissues.
