Step 1: Understanding the Concept
Plants use devices to avoid self-pollination in bisexual flowers.
Step 2: Match the device
When anthers and stigma mature at different times, it is called dichogamy.
If anthers mature first it is protandry, and if the stigma matures first it is protogyny.
Step 3: Other terms
Herkogamy is a physical barrier between anther and stigma, heteromorphy is different flower forms, and unisexuality means separate male and female flowers.
Step 4: Conclusion
The device is dichogamy.
Final Answer:
The device is dichogamy.
\[ \boxed{\text{(B) }\text{Dichogamy}} \]