Heterostyly is a condition found in some angiosperms (flowering plants) of having styles of different lengths. The classic example of heterostyly is the primrose Primula vulgaris, in which there are two distinct flower forms, each occurring on different plants. Each form has a different-sized sty;le and stamen from the other so that pollen collected by insects from the anther of one type is dropped on the stigma of the other. Heterostyly increases the likelihood of cross-pollination because pollen cannot be passed between plants with sex organs of the same size.