SCANNING ELECTRON MICROSCOPIC STUDY OF THE EARLY EVENTS IN GRAFT FORMATION.

A scanning electron microscopical study of a compatible autograft in Sedum telephoides was performed in order to characterize the earliest events that occur during the formation of a compatible graft union. The initial cohesion between the stock and scion occurs in the pith region within 24 hours after grafting and is positively correlated with the onset of callus proliferation in both graft partners. By 3 days after grafting, callus proliferation in the cortex 'fills in' much of the cortical area of the graft interface. By 6 days after grafting, continued callus proliferation at the graft union typically results in the graft union having a greater diameter than that of the adjacent stem. Redifferentiation of vascular tissue across the graft interface occurs subsequent to 6 days after grafting.