Observations of the germination of zoospores from the zoosporangia of Phytophthora infestans (MONT.) DEBARY, which were suspended, in 0.005% ATP and 5x10^<-4> M DNP solution, were carried out under phase-contrast microscope. The move ment of granules (which seemed to be mitochondria through vital staining of 0.0005% Janus Green B solution) and the percentage of sporangial germination was raised by the addition of ATP and was inhibited by DNP solution.
After the zoospores were inoculated to the surface of the cut end of the leaf petiole of potato plants (Variety Irish Cobbler), DNP and ATP were introduced to them with pressure. In the former case, the mycelial growth of the pathogen within the suscept plants was delayed, and in the latter case it was accelerated.
To investigate the invasion of pathogens to potato tubers, the late-blight fungus was inoculated to the cut surface of potato tubers (Varieties used were - Kennebec, Hybrid 4702-7 and 41089-8 as resitant; Irish Cobbler as susceptible) and they were kept at 20℃ for 7 days. Observatioins were undertaken under phase-contrast and polarization microscopes. Double refraction in the invaded parts in the resistant varieties was stronger than in the susceptible one. The possibility of the change of micellar arrangement or structure in the cytoplasm of resitant varieties was taken into consideration from these investigations.