In 1949, Roald Dahl wrote a short story called "The Sound Machine" (PDF). In it, a man invents a machine that allows him to hear the sounds inaudible to humans due to their frequency outside the range of hearing, and discovers that plants do, in fact, make sound in response to the world.
Artist Leslie Garcia's "Pulsu(m) Plantae" has not, in fact, revealed that plants make noise. Instead, Garcia has analyzed the physiological response of plants to certain external stimuli and created a real-time "audio prosthetic" -- that is, a device that translates the plant's responses into audible sound.
It consists of sensors to monitor the plants' biofeedback; a transducer (a device that converts those readings into sound); and amplifiers to play those sounds to the listener. Garcia found that plants emit different-sounding reactions to touch, sound, and light.
She also found that the plants "hum" to each other when their vessels are connected. Just changing which plants are connected can change the quality of the sound.
The idea that plants can "feel" is certainly not a new one; we can even see plants physically respond to light and water. Garcia's work, however, gives the concept an immediacy and sense of realness that may make you think twice before plucking a flower or walking on the grass when there's a perfectly serviceable path available.
(Source: Crave Australia)