(1) The relative rate of growth of pollen tubes in the style, of selfed and crossed flowers in the Japanese pears, Chojuro, Nijisseki, and Waseaka was determined. (2) The pollen tubes travelled down nearly to the base of style in self pollina-tion, though their. progress was very slightly slower than that in cross pollination, but then their growth was decidedly arrested so that they could not force their wayy into the ovary. (3) In a greenhouse of about 70° F. the pollen tubes progressed down in the style nearly twice as fast as those in open air in the first 24 hours, but after that their growth rate was decidedly depressed and no tubes penetrated into the ovary in self pollination. (4) The behaviour of growth of pollen tubes in the incompatible crosses, Ichiharawase×Meigetsu, and Taihaku × Waseaka, was examined. (5) The progress of pollen tubes in the style was slower in incompatible than in compatible crosses and the retardation of pollen-tube growth occurred more remarkably in the case of cross-incompatibility than in that of self-incompatibility, yet the pollen tubes had traversed more than two thirds of the entire distance in the styles collected 7 days after pollination in cross-incompatibility. (6) The pollen tubes which formed a swollen end were seen in both com-patible and incompatible pollination, but they appeared more frequently in the styles in incompatible pollination, and they were not found in the styles collected early after pollination in compatible as well as in incompatible pollination, and as the style was collected later, they appeared therein more frequently in incompatible pollinations.