The pollen tube growth in interspecific pollination was investigated to assess interspecific cross-incompatibility among ten species at the prezygotic stage and also to analyze the evolutional relationship between self-incompatible (SI) and self-compatible (SC) species. Total 136 pollination treatments were conducted under pollinator-free conditions at the full flowering stage. Florets were harvested 4 or 24 hours after pollination, and pollen tube length was measured under a fluorescent microscope. Measurements were made on the longest pollen tube for each style, and 6-36 styles were observed per pollination treatment. The following conclusions were derived from this study. 1) Unilateral incompatibility was observed among the SI and SC species. ing, it is important to analyze the relationship between 2) Dimorphic self-incompatibility system influenced the re-cross-incompatibility and self-incompatibility