Slowly, please.
Scientists in Bonn have developed a method of listening to sounds from plants normally inaudible to the human ear. The basic technique was developed in the Netherlands, but the German equipment is more sensitive. When a leaf or stem is sliced, the plant signals pain or dismay by releasing the gas ethylene over its entire surface. The gas molecules are collected in a bell jar and bombarded with laser beams, which makes them vibrate. The resultant sound waves are amplified in a resonance tube, and detected with a sensitive microphone. The longer a plant is subjected to stress, the louder the signal.
One surprising result came from an apparently healthy cucumber that was virtually shouting with agony. A closer study showed it has developed mildew, a harmful fungus, though the symptoms were not apparent. Listening to plants in this way could be of great benefit to farmers as an early-warning system to detect pests and disease, and as an aid to efficient storing and transporting. Apples, for instance, give off high levels of ethylene, increasing with ripeness and causing neighbouring fruit to rot. Invisible differences of ripeness may be detected acoustically, enabling fruit to be separated into batches in order to prolong its freshness.
