Abstract:Electrical resistance changes in concert with the histological changes during the development of graft union. Four phases of change in electrical resistance of the compatible graft were demonstrated. Phase Ⅰ: There was a slight decrease of the electrical resistance, lasting about several hours. Phase Ⅱ The resistance values increase rapidly, lasting for two days or so. Phase Ⅲ: In the next four days, the resistance values decreased progressively. Phase Ⅳ: The resistance values levelled off and approximated equal to the level before grafting. In contrast to the compatible grafts, three types of resistance change were observed in the incompatible graft: (1) The resistance values increased rapidly on the first day after grafting but only slightly afterwards decreased. (2) The electrical resistance rose rapidly to its peak on the first day after grafting and decreased rapidly in 2--3 days followed by steady increase again. (3) The change of resistance follows the track as in (2) for 2--3 days and then increased rapidly afterwards. The results suggested that measurement of electrical resistance could be useful tool for the detection of graft compatibility/incompatibility in commercial practice and basic research of plant grafting.