Question 4
In passion fruit, no fruit forms when a flower's own pollen is deposited on its own stigma. What is this adaptation called?
The right answer is the one marked above.
Self-sterility. The pollination happens; the fruit simply does not follow.
Herkogamy would place the stamens and stigma far apart — spider lily and orchid. Dichogamy would ripen them at different times. Unisexuality would put them in separate flowers altogether. All four prevent self-pollination, but only this one lets it happen and then refuses the result.