The present paper deals with the results of electron-microscopic observations of cell wall of potato plant. The epidermal cell walls of petiole midribs infected with Phytophthora infestans (Mont.) DeBary were treated with ethanol, ethanolamine, Na-OH and HCl, and examined under electron microscope using the technique of replication. At the same time the healthy walls were examined in the same way. For shadowing, Cr. or Pt-Pd were used and shadow-angles were 25 degrees. Shadowing films were examined with HS-6 electron mocroscope.
1. The linear structure were recognized on cell wall. The lines on cell wall run parallel to longitudinal cell wall or run almost at right angle to each other. The lines on cell wall have many swellings and have 4,000-15,000 A^^゜ in diameter.
2. Cellulose microfibrils are the basic structural unit of cell wall. The microfibrils interwave almost at right angle to each other. Besides this, paralleled microfibrils or the mocrofibrils of various degrees against the axis of main microfibrils were investigated. Microfibrils have 100-200 A^^゜ , and microfibres have 2,000-3,000A^^゜ in diameter.
3. Within the scope of these observations, there is no difference on the basic structure of cell wall between the resistant and susceptible varieties of potato plant. And there was no evidence of changing the fine structure of microfibrils both in resistant and susceptible varieties after the invasion of Phytophthora infestans.