Q.What are outbreeding devices? Name any three such devices found in flowering plants.

They evolved because continued self-pollination reduces vigour and fertility over generations.

Outbreeding devices are structural, temporal or genetic mechanisms that flowering plants have evolved to prevent or discourage self-pollination (autogamy) and to promote cross-pollination (xenogamy) instead. They exist because continued generations of self-pollination tend to reduce a population's vigour and fertility, whereas cross-pollination introduces genetic variation.

Three commonly cited outbreeding devices are: dichogamy, where the anthers and stigma of the same flower mature at different times so both are never receptive together; herkogamy, where the anthers and stigma are positioned so as to physically prevent self-pollen from reaching the stigma even though both are mature at the same time; and self-incompatibility, a genetic/physiological mechanism by which the pistil prevents self-pollen (or genetically similar pollen) from achieving fertilisation even after landing on the stigma. (Dioecy -- bearing male and female flowers on entirely separate plants -- is a further device that rules out both autogamy and geitonogamy.)

Define the purpose (prevent self-pollination, favour cross) first, then name and briefly characterise three distinct mechanisms.

Listing dioecy and self-incompatibility as the same thing -- dioecy is a structural/morphological separation (separate plants), while self-incompatibility is a physiological/genetic recognition mechanism.