The existence of two or more different arrangements of the reproductive parts of a flower in one species. These differences are often related to the position assumed by the pollinating agent when visiting the flower. For example, in Primula two different arrangements are found (see illustration), one where the style is long and the stamens inserted at the base of the corolla on short filaments (pin), and the other where the style is short and the stamens are inserted in an almost sessile fashion on the neck of the corolla (thrum). The different arrangements were thought to ensure cross pollination between the different types. Recent evidence does not support this hypothesis although the differences do appear to reinforce existing physiological barriers to self fertilization. See incompatibility, allogamy.  |
