A series of experiments at the Massachusetts Institute of Technology demonstrated that rice seeds sprouted faster to the sound of rainfall.

The sound of falling droplets effectively shook the seeds out of a dormant state, stimulating them to germinate at a faster rate compared with seeds that were not exposed to the same sound vibrations.

The findings, published yesterday in the journal Scientific Reports, are the first direct evidence that plant seeds and seedlings can sense sounds in nature.

Rice seeds can germinate in either soil or water, and these experiments involved seeds submerged in shallow water.

The researchers suspect that many similar seed types may also respond to the sound of rain.

The MIT team found that when a raindrop hits the surface of a puddle or the ground, it generates a sound wave that makes the surroundings vibrate, including any shallowly submerged seeds.

The vibrations can be strong enough to dislodge a seed's "statoliths", tiny gravity-sensing organelles within certain cells of a seed. When the statoliths are jostled, their movement is a signal for seeds and seedlings to grow and sprout.

"The energy of the rain sound is enough to accelerate a seed's growth," said study author Professor Nicholas Makris.

"What this study is saying is that seeds can sense sound in ways that can help them survive."

Plants have evolved to sense and respond to many stimuli in their surroundings to help them survive: some plants snap shut when touched, some curl inward when exposed to toxic smells, and most respond to light, reaching toward the sun to help them grow.

Prof. Makris says plants can also sense gravity. A plant's roots grow down, while its shoots push up against gravity's pull.

One way that plants sense and respond to gravity is through their statoliths, which are denser than a cell's cytoplasm and can drift and sink through the cell, like sand in a jar of water.

When a statolith finally settles to the bottom, its resting place on the cell's membrane is a reflection of gravity's direction and a signal for where a seed's root or shoot should grow.

Makris became curious when Cadine Navarro, an MIT graduate, asked him about seeds and sound. They wondered if sound could be enough to jostle the statoliths and stimulate a seed to grow.

"I went back to look at work done by colleagues in the 1980s, who measured the sound of rain underwater," explained Makris. "If you check, you'll see it's much greater than in the air.