Three Devices Encouraging Cross-pollination in Angiosperms:
1. Dioecy: Separate male and female flowers on different plants, preventing self-pollination.
Examples: Willow, spinach, hemp.
2. Dichogamy: Timing mismatch between pollen release and stigma receptivity.
3. Hermaphroditism with Structural Barriers: Physical separation of male and female parts within the same flower.
Examples: Hibiscus, iris, snapdragon.
Bonus:
Self-incompatibility: Genetic mechanisms preventing pollen from the same plant from fertilizing the egg cell.