Cut pieces of potato tubers were preserved at a temperature of 30℃ and humidity of 85~97 % for 8 days. The whole surfaces of wounded parts were covered with wound cork, and healed perfectly. Then the tops of the pieces of potato tubers were cut again, and about 0.2 cc of water suspensions either of Erwinia aroideae, Pseudomonas solanacearum or Corynebacterium sepedonicum was inoculated with pipetts at one hour intervals. Experimental data are shown in Table 1 to Table 6. The penetration of pathogenic bacteria from the wound of potato tuber became considerably difficult 8 hours after wounding.