Introduction:
Flowering plants have evolved various mechanisms to prevent self-pollination and encourage cross-pollination. These adaptations are known as outbreeding devices and are important for genetic diversity and the survival of plant species. Three examples of such outbreeding devices are dicliny, dichogamy, and herkogamy. However, cleistogamy is not an example of an outbreeding device.

Dicliny:
Dicliny refers to the separation of male and female reproductive structures on different flowers. In some plants, the male flowers (staminate flowers) and female flowers (pistillate flowers) are borne on separate individuals. This is known as dioecy. In other plants, both types of flowers are present on the same individual but in separate inflorescences. This is known as monoecy. Dicliny ensures that pollen from one plant is transferred to the female flowers of another plant, promoting cross-pollination.

Dichogamy:
Dichogamy refers to the temporal separation of male and female reproductive structures within the same flower. In protandry, the male reproductive structures (anthers) mature before the female reproductive structures (stigma). This prevents self-pollination as the pollen is no longer viable by the time the stigma becomes receptive. In protogyny, the female reproductive structures mature before the male reproductive structures, achieving the same outcome.

Herkogamy:
Herkogamy refers to the physical separation of male and female reproductive structures within the same flower. This can be achieved through various mechanisms such as the position of the anthers and stigma or the presence of barriers like hairs or spurs. By physically separating the male and female parts of the flower, herkogamy reduces the chances of self-pollination and promotes cross-pollination.

Cleistogamy:
Cleistogamy is not an example of an outbreeding device. It is a reproductive strategy where plants produce self-pollinating flowers that do not open and remain enclosed within the bud. The flowers in cleistogamous plants are typically small and inconspicuous. Since these flowers do not open, there is no opportunity for cross-pollination to occur. Cleistogamy is adaptive in environments where pollinators are scarce or unreliable, as it ensures reproductive success even without external pollination.

Conclusion:
In conclusion, flowering plants have evolved various outbreeding devices to discourage self-pollination and encourage cross-pollination. Dicliny, dichogamy, and herkogamy are examples of such mechanisms. However, cleistogamy is not an outbreeding device as it involves self-pollination without the involvement of external pollinators. These adaptations play a crucial role in maintaining genetic diversity and the survival of plant species.