We set up an experimental forest in the coppice near the Tokyo College of Agriculture and Forestry, July 1948. We surveyed how vast aecidio-spore of Cronartium quercuum spread over, and how it attacked “Konara” (Quercus serrata) and “Kunugi” (Qurcus acutissima) which were intermediate hosts of the fungi. We would show the outline of the methods and the results as follows. Methods: We selected diseased ones from “Akamatsu” (Pinus densiflora) in the experimental forest, and figured them on the map of the forest. At the same time. we chose a number of the “Konara” and “Kunugi” in the forest, and sorted out various infection-grade according to a certain standard, which we determined to make an entry it. We measured the distance of of the infected “Konara” and “Kunugi” from diseased “Akamatsu” by the above map. Results: