Plant Perception

It's more sophisticated than you'd think. Daniel Chamovitz, author of What a Plant Knows, elaborates on their extraordinary sense of "smell":

You may have heard that if you put a ripe and an unripe fruit together in the same bag, the unripe one will ripen faster. This happens because the ripe one releases a ripening pheromone into the air, and the green fruit smells it and then starts ripening itself. This happens not only in our kitchens, but also, or even primarily, in nature. When one fruit starts to ripen, it releases this hormone which is called ethylene, which is sensed by neighboring fruits, until entire trees and groves ripen more or less in synchrony.