Q.Describe outbreeding devices which encourage cross pollination.

Flowering plants have evolved a range of structural, temporal and genetic devices specifically to reduce self-pollination and favour cross-pollination instead. …

Many flowering plants have evolved mechanisms to avoid the reduced genetic variability associated with continuous self-pollination, favouring cross-pollination instead. Dicliny (unisexuality) is the most direct device: in dioecious species, male and female flowers occur on entirely separate plants (e.g. papaya, mulberry), making self-pollination structurally impossible; in monoecious species, male and female flowers occur on the same plant but at different locations (e.g. tassel and ear in maize, separate male and female flowers in cucurbits), reducing (though not eliminating) self-pollination. Dichogamy is a temporal separation, where the male part (anther, releasing pollen) and the female part (stigma, receptive) of a bisexual flower mature at different times, preventing self-pollen from fertilising the same flower's stigma; if the anthers mature before the stigma, it is called protandry, and if the stigma matures before the anthers, it is called protogyny. Herkogamy is a structural device in which the anthers and stigma of a bisexual flower are physically positioned or shaped so that self-pollen cannot easily reach the stigma of the same flower. Heterostyly is a genetic polymorphism in which different individual plants of the same species produce flowers with styles and stamens of contrasting relative lengths (e.g. pin-eyed and thrum-eyed flowers in Primula), so that efficient pollen transfer (by an insect pollinator) tends to occur only between flowers of different, complementary types, favouring cross-pollination. Self-incompatibility is a genetic/physiological mechanism by which a plant's own pollen, ev …