UWA

The University of Western Australia's Monica Gagliano studies how plants communicate with each other.

Studies show that basil gives a boost to chili peppers, while fennel is a real bummer. The effect has been seen even when the plants are sealed off from each other with sheets of black plastic. So does that mean that the plants are "talking" to each other through subtle vibrations? That's the kind of talk that sparks a debate — not between the plants, but between humans.

The latest study, reported in the open-access journal BMC Ecology, looked at potential communication between basil plants and chili pepper seeds. It's one of a series of experiments conducted by Monica Gagliano and Michael Renton of the University of Western Australia.

"Our results show that plants are able to positively influence growth of seeds by some as-yet unknown mechanism," Gagliano said in a news release from BioMed Central, the journal's publisher. "Bad neighbors, such as fennel, prevent chili seed germination in the same way."

Fennel plants release chemicals into the air and soil that are detrimental to most other plants, including chili peppers. Last year, Gagliano and her colleagues set up mini-gardens to study the interaction between the plants more closely. They were surprised to find that chili seeds germinated more quickly when the fennel plant was sealed off with plastic to block the transfer of those nasty chemicals. It was almost as if the baby chilis sensed that a villainous plant was nearby, and grew up faster so they'd have a better chance of fending off the fennel.

The new study looks at the flip side of plant interaction: Unlike fennel, basil is a "good neighbor" for chili plants because basil plants release chemicals that discourage weed growth. Gagliano and her colleagues found that to be the case for chili seedlings. The seeds germinated at a higher rate, even if the basil plant was sealed off with the black plastic. That led Gagliano and Renton to conclude that the seeds could still sense the presence of a friendly plant when they couldn't get the standard chemical signals.

How could this be?

"We believe that the answer may involve acoustic signals generated using nanomechanical oscillations from inside the cell which allow rapid communication between nearby plants," Gagliano said in the news release.

That surmise seems to fit with other findings on plant communication. Corn roots, for example, give off regular clicking sounds in the range of 220Hz (which corresponds to an A below middle C). Gagliano and her colleagues found that when young corn roots are suspended in water, they tend to lean toward the source of a continuous 220Hz tone transmitted through the water. The researchers suggested that acoustic signals could knit plants into an underground network of friends and foes.

But as Gagliano points out, no one has yet identified the precise mechanism by which one plant hears what another plant is saying. That's one of the reasons why other researchers haven't wholeheartedly embraced the idea that plants are talking to each other.

"Although the idea of plants communicating by sound is intriguing, there is still a long way to go before we know whether, and if so to whom, the woods sing!" the University of Leiden's Carel ten Cate wrote last December in the journal Behavioral Ecology.

Duke University's Dan Johnson, who is studying how trees respond to drought, said it's "too early to tell" whether plants truly respond to each other's sounds.

"We have been detecting these acoustic signals for almost 50 years," Johnson told NBC News. "The idea of using those signals for communication is incredibly interesting, and there is potentially some growing support for it. But we're a good ways away from strong support for acoustic signaling between plants. ... I'm glad that somebody's working on it, but I think it's too early to say."

More about plant communication:

• Hear that sound? That's a thirsty tree
• Listen up: This is your plant talking!
• Plant uses sound to attract bats
• Flowers and bees have electrifying discussions

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the NBC News Science Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with NBCNews.com's stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

Scott Thompson / Maryhill Museum file

Maryhill Museum's concrete replica of Stonehenge was designed to duplicate the ancient English monument.

British researchers conducted experiments at a Stonehenge stand-in as well as the actual 5,000-year-old monument to determine how sounds echoed within the ancient circle of stones — and they found that the sounds would have taken on an eerie reverberation.

"We can expect such a space to have a striking effect on someone of that time, identical to what we feel nowadays when we go into a church," the University of Salford's Bruno Fazenda, who orchestrated the research project, told me in an email.

The study is described on the university's website in a technical analysis as well as a news release issued last week, but the upshot is that the Neolithic people who gathered inside the circle could well have had a religious aural experience. That meshes with the view of most archaeologists that the monument on England's Salisbury Plain took on the trappings of a place of healing — a "Neolithic Lourdes," if you will.

It's not easy to reconstruct the sounds of ancient Stonehenge: For one thing, many of the standing stones are missing from what was thought to be their original places, ruining the acoustic arrangement. For another thing, researchers are not allowed to run electrical power out to the site, or bring in a generator. That limits the types of sound equipment and scientific instruments that can be used on site.

Replicating the reverb
Fazenda and his colleagues from the University of Huddersfield and the University of Bristol found a couple of clever solutions to those challenges. They brought air-filled balloons to the Stonehenge site in 2009, then popped the balloons with a needle and recorded the reverb with a microphone and a digital field recorder. The reflected sounds of the pops were hard to make out, but they appeared to follow a pattern of 1-second reverberation time at midfrequencies, for locations that were within the ruins of the stone circle.

To study the reverberation patterns in detail, the team headed off to the Maryhill Museum in Goldendale, Wash., which has a full-scale concrete replica of Stonehenge on its grounds. The monument was built by millionaire industrialist Samuel Hill as a tribute to fallen World War I servicemen. The museum let the researchers make their measurements with more sensitive instruments, powered by on-site generators. The same balloon-popping technique was used, and the readings confirmed the reverberation pattern that the team found at the real Stonehenge.

"For an outdoor space, the stone circle exhibits quite a 'live' acoustic environment," Fazenda said. "In the Neolithic, such an environment was not very common at all. The only spaces that might sustain reverberation were caves and perhaps some natural features such as opposing cliff faces."

Fazenda said the echo effect would be much more like what you hear in a cathedral than in a concert hall.

"The center of the space has potential for some focusing effects," he said. "That's the point where all reflections arrive at the same time, and with the largest gap relative to direct sound. On paper we would expect that to sound striking. However, there are quite a lot of scattering effects from the stones, so the clear echoes are somewhat destroyed by it."

He stressed that it's not at all clear whether Stonehenge was designed with the acoustics in mind, but he and his colleagues do think that the setting would have added a special something to drumbeats, chants or music inside the stone circle.   

'Research hobby'
Fazenda, who teaches audio production at Salford, has been working on this project for the past four years on an unfunded basis. "It has been a kind of 'research hobby' that I have managed to do after hours (don't really call it spare time)," he wrote. He believes the project could break new ground in the field of archaeoacoustics — the study of the sound characteristics of ancient spaces.

"The original focus was on studying the acoustic response of the space," he said. "The recent output has been that we replicated it using wavefield synthesis, which immerses you in a sound field, thus giving you the most approximate aural experience that you could get of being in the space. That was shown at a few recent events, and we have a permanent demo in our labs here at Salford. A wavefield synthesis system uses +64 channels and speakers, so it is not really portable."

Such a system can be tuned to provide a virtual-reality sense of the sounds of Stonehenge, as well as the sounds of other ancient settings that are no longer configured the way they were in their heyday. Want to hear the roar of the crowd in the Roman Colosseum? There's a wavefield synthesis app for that.

Fazenda is preparing a paper on his "research hobby" for Acta Acustica, the journal of the European Acoustics Association. He's also writing a chapter for a book on the acoustics and music of British prehistory. (For more on that subject, check out the website of the Acoustics and Music of British Prehistory Research Network.)

You can expect to hear more about the sounds of Stonehenge in the months and years ahead. In the meantime, give a listen to these sound files, and follow the Web links for more about archaeoacoustics.

Stonehenge sound files:

• Hand-clapping outside and inside the Maryhill stone circle (via Sonic Wonders)
• Univ. of Salford's rendering of a song with Stonehenge-style reverb (WAV file)
• Sounds of Stonehenge ... including a podcast on sound heritage

More about archaeoacoustics:

• Scientists revive sacred sounds
• Was Stonehenge inspired by a sound illusion?
• It turns out that cavemen loved to sing
• Stonehenge: Totally awesome place for raves
• Researchers re-create scary pre-Columbian sounds
• Acoustic archaeology yields mind-tripping tricks
• Listen to the sounds of science

Alan Boyle is msnbc.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter or adding Cosmic Log's Google+ page to your circle. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for other worlds.

Stanford University

A researcher sounds a note on a conch-shell trumpet as part of an experiment to re-create the ceremonial calls heard by ancient Andeans in the Chavin de Huantar ceremonial center in Peru.

Ancient peoples around the world seem to have designed their sacred spaces not only for ceremonial sights, but for ceremonial sounds as well, archaeologists say.

In Peru, for example, a 3,000-year-old Andean ceremonial center's design was optimized for the blare of a priest's conch-shell trumpet. In Mexico, the Chichen Itza temple site features a staircase that can make hand claps sound like the chirp of a quetzal bird. And one of the best-known ancient monuments of all, England's Stonehenge, has a layout that's acoustically pleasing as well as astronomically significant.

The big question is, did ancient societies really have acoustics in mind when they built their monuments?

"That is a challenge," said David Lubman, a California-based acoustical scientist and consultant. Much of the evidence is circumstantial, or based on interpretations of ancient myths. But when the acoustical resonances fit so well with the purpose of a ceremonial space, it's hard to resist making a connection.

"Whether or not you have historical evidence, you have another form of evidence," said Miriam Kolar, a researcher at Stanford University's Center for Computer Research in Music and Acoustics.

Theater for the ears
Researchers discussed their efforts to unravel the mysteries of ancient acoustics today at the annual meeting of the American Association for the Advancement of Science, held in Vancouver, British Columbia.

For the past few years, Kolar and her colleagues have been focusing on Chavin de Huantar, a pre-Inca site in Peru that served as a regional religious center. People apparently came to a circular plaza to worship, and to hear an oracle's pronouncements issuing from a stone gallery.

The Stanford team conducted a detailed acoustical study of the gallery's cross-shaped passageways. They found that the central duct between the gallery and the plaza would serve as an acoustic filter system, accentuating the tones produced by the priests' ceremonial conch trumpets, known as "pututus."

"There was theater going on," Kolar said. The thrilling effect of the trumpet calls and the oracle's words may well have been heightened by the psychoactive effects of the San Pedro cactus that the Chavin people consumed during their rituals.

The chirping staircase
There are theatrical touches as well at Chichen Itza, a Maya temple complex going back more than 1,000 years, Lubman said. One of the most prominent monuments is the Temple of Kukulkan, also known as El Castillo: Some researchers have argued that the temple's staircase was constructed so as to create a "feathered serpent" shadow during the spring and autumn equinoxes. Lubman says the staircase can produce an aural as well as a visual effect: When you clap your hands at just the right spot, the echo comes back sounding much like the chirp of the quetzal bird, which was sacred to the Maya.

The acoustician played an audio clip demonstrating that the bird's chirp and the clap's echo sounded remarkably similar. He speculated that a priest might have clapped his hands loudly to seek counsel from a quetzal. Worshipers would have been impressed to hear the chirp of a spectral bird, apparently coming from inside the temple. "Only priests were trained to interpret what the quetzal said," Lubman said, half-jokingly.

Lubman has been studying Chichen Itza's acoustics for more than a decade. That's such a long time that the quetzal research "should be old news," he said. "But the darn bird keeps chirping." He noted that Chichen Itza has another interesting acoustic feature: Its ball court is designed like a "whispering gallery," so that a low utterance in one corner of the court could be heard clearly in another corner.

The bottom line? Maybe the ancient Maya were more in tune with sacred sounds than we are today. "Now, many things go through our eyes before they get to our minds, but that wasn't true in the ancient world," he said.

The Stone Age and Stonehenge
Steven Waller, a researcher at California-based Rock Art Acoustics, theorized that acoustics may even have had something to do with the placement of the stones at Stonehenge, a monument that's at least 5,000 years old. "What struck me was that the layout of Stonehenge reminded me of an interference pattern," he told his AAAS audience.

Waller said he was even more intrigued when he considered the legends of ancient Britain. One legend suggests that Stonehenge was created when two pipers lured maidens into a circle with their magic tunes, and then turned them into standing stones. He noted that some of Stonehenge's monoliths are sometimes called "piper stones."

Could ancient acoustics have been behind some of these legends? To find out, Waller conducted an experiment in which he put blindfolds on experimental subjects and had them walk around an open field in a circle while two flutes played an identical tone (1100 Hz, or C-sharp). The sound waves from the two flutes interfered with each other in such a way that the sound alternated between loud and soft in different locations. When the walkers were asked to map out the area, they came up with a pattern of obstacles and archways much like an ancient stone circle.

"It's as if there was something blocking the sound ... a ring of invisible objects, massive objects, blocking the sound," he said.

Waller also analyzed the placements of stones at Stonehenge and other neolithic stone circles, and found the acoustic parallel he was looking for. "The pillars actually cast acoustic patterns that mirror an interference pattern," he said.

The leading hypothesis about Stonehenge is that it served as a religious center that was laid out to mark the astronomical alignments for Earth's seasons, and Waller doesn't take issue with that. "My theory doesn't necessarily conflict with the solar alignment theory," he said. But is there any evidence to show that Stonehenge's designers really did have acoustics in mind? Waller can only point to the circumstantial connections — for example, the fact that cave paintings were often put in the locations that had the best acoustics for ceremonies, or the fact that some ancient peoples thought echoes emanated from spirits inside stones.

"They didn't know about sound waves reflecting," he said.

Waller said the important thing is to be mindful of the contributions that acoustics can make to the study of sacred spaces. Some of those spaces are already in danger of disappearing. For example, Waller worried that some of the modern-day renovations aimed at making cave paintings in France more accessible to tourists may actually destroy the acoustic qualities that led the painters to those spots in the first place.

"Nobody has been paying attention to the sounds," he said. "We've been destroying the sounds."

More about the sounds of science:

• It turns out that cavemen loved to sing
• Was Stonehenge inspired by a sound illusion?
• Stonehenge: Totally awesome place for raves
• Researchers re-create scary pre-Columbian sounds
• Acoustic archaeology yields mind-tripping tricks
• Listen to the sounds of science

Alan Boyle is msnbc.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter or adding Cosmic Log's Google+ page to your circle. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for other worlds.