Self-Pollination:
Self-pollination is the process in which the transfer of pollen grains from the anther to the stigma occurs within the same flower or between flowers of the same plant. This ensures the fertilization and reproduction of the plant. There are several mechanisms that plants employ to ensure self-pollination:

1. Cleistogamy: Some plants have flowers that never open, known as cleistogamous flowers. These flowers have specialized mechanisms where the anthers release pollen directly onto the stigma without the need for external agents like wind or insects.

2. Herkogamy: Herkogamy refers to the physical separation of the anther and stigma within the same flower. This prevents the pollen from being easily transferred to other flowers. The separation can be achieved through various means such as differences in position, length, or curvature of the reproductive organs.

3. Homogamy: Homogamy is the condition in which the anthers and stigma mature simultaneously, ensuring that self-pollination occurs before the flower opens and before the pollen is exposed to external factors like wind or insects.

Cross-Pollination:
Cross-pollination is the transfer of pollen grains from the anther of one flower to the stigma of another flower on a different plant of the same species. This method of pollination promotes genetic diversity and increases the chances of successful reproduction. Plants employ various strategies to ensure cross-pollination:

1. Floral Morphology: Many plants have evolved specific floral structures to facilitate cross-pollination. These structures may include mechanisms like nectar guides, which guide pollinators towards the reproductive organs, or specialized shapes that require specific pollinators for successful pollination.

2. Wind Pollination: Some plants, especially those with small, inconspicuous flowers, rely on wind for pollination. These plants produce large quantities of lightweight and dry pollen grains that are easily carried by the wind to other plants. They often have long, feathery stigmas to capture the airborne pollen.

3. Insect Pollination: Many plants have co-evolved with insects to ensure cross-pollination. These plants produce attractive flowers with bright colors, sweet scents, and nectar to lure insects. The insects inadvertently transfer pollen between flowers as they move from one flower to another in search of food.

4. Animal Pollination: Some plants rely on animals like birds, bats, or small mammals for pollination. These plants often have specialized adaptations to attract specific animals, such as brightly colored flowers, strong fragrances, or tubular shapes that fit the beaks or tongues of particular animal pollinators.

In conclusion, plants employ various mechanisms to ensure self-pollination or cross-pollination. Self-pollination is achieved through mechanisms like cleistogamy, herkogamy, or homogamy, while cross-pollination is facilitated through floral morphology, wind pollination, insect pollination, or animal pollination. These diverse strategies ensure the successful reproduction and genetic diversity of plants.