Mesophyll cells about 2mm around mechanical wound of the edge of leaf discs were killed and new chemical wound formed the discs were immersed in 0.1% HgCl_2 for 80 secands. The chemical wound became brown and wilt, and the forming ability of its callus was also inhibited completly after the discs were cultured for 4 to 7 days. However, callus and seedlings within leaf discs could grow wherever micromechanical wound was made. Twelve percent H_2O_2 and 100mg/ml Kanamycin had the same function.