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PRI's Environmental News Magazine

Exploding Plants

Air Date: Week of November 11, 2011

stream/download this segment as an MP3 file

Caption: Sphagnum capsules in various stages: maturing, swollen, and exploded. (Photo: Laurie Sanders)

Biologist Joan Edwards likes to look closely at plants, and particularly, plants that move fast. Her research at Williams College focuses on the mechanism of exploding plants, including sphagnum moss. Producer Laurie Sanders joined Edwards in the field and lab to see some fast action.

Transcript

GELLERMAN: As a rule, most plants move in slow-mo and go with the flow of wind and water slowly. But reporter Laurie Sanders met one researcher who studies plants that are down right speedy.

SANDERS: Joan Edwards never imagined her research would end up in the Guinness Book of World Records. But in 2005, Edwards discovered the world’s fastest opening flower - a common plant in the northern woods known as bunchberry, with blossoms that pop open in less than half a millisecond. The finding was, in part, serendipitous, but Edwards says it's had since had an important influence on her research ever since.

EDWARDS: We realized there were other mechanisms by which plants move very, very rapidly. And so started to look at all the different ways that they could move rapidly and also tried to figure out, why do they do it? What’s the point? Is there some sort of selective advantage for these plants to doing something very, very rapidly? And they do this, of course, all without muscles.

SANDERS: Since then, Edwards has spent a lot of her time trying to answer those questions.

[SCRAMBLING SOUND, SOUNDS OF WATER SWIRLING]

SANDERS: One of the plants she’s studying is sphagnum moss. It’s another fast-action plant. Today, we’re visiting a small bog in Pownal, Vermont where she’s hoping to find sphagnum moss in fruit.


The explosion: five frames from a video taken at 10,000 frames per second. Included is every second video-- so from the first to the last frame it is a fast 8/10,000th of a second! (Courtesy of Joan Edwards)

EDWARDS: We’re going to want to look for now are little tiny capsules, and the capsules are about the size of … slightly smaller than a pepper grain - maybe half the size of a pepper grain. And they are very explosive. Up - there are some right here. Unbelievable. We barely stepped onto the bog.

SANDERS: Although you may have never visited a bog, you may have had a firsthand encounter with sphagnum moss. When it’s harvested and dried, it’s sold in garden stores as peat moss. Here, and in bogs everywhere, sphagnum moss is the dominant plant.

[SOUNDS OF WALKING IN A BOG]

EDWARDS: A lot of these have exploded. You see these columnar ones…

SANDERS: Some of the sphagnum stems Edwards is finding today have five or six capsules.

EDWARDS: The round ones haven’t yet exploded. And what will happen is that when they get ready to explode, first of all, they elongate the stalk that they’re on. So they get up above the moss mat and then they gradually dry out and they go from perfectly spherical to columnar. So it gets squished in from the sides, and when the pressure inside builds up, it blows its cap up into the air, as high as maybe 15 cm.

[SOUND OF THUNDER]

SANDERS: The skies open up,

[SOUNDS OF RAIN, THUDNER]

SANDERS: So we decide to head back to Edwards’ lab at Williams College in Western Massachusetts. As we scramble our way out of the bog, she pauses at another cluster of fruiting sphagnum.

EDWARDS: And I’m sure one of these is going to be a record exploder. They’re never going to explode in this rain, though. They need sunshine. Lots of sunshine.

[CLANKING SOUND]

SANDERS: Back in her lab, one of the tools Edwards uses is a high-speed camera. It’s the same kind of camera that’s used to study ballistics or in industry, to see how machinery parts mesh together.

EDWARDS: So the way this works is we have a camera that will go as high as 100,000 frames per second, which is pretty incredible.


This sphagnum moss capsule has yet to explode. (Photo: Laurie Sanders)

SANDERS: At such high speeds, Edwards can film the action and by replaying it at a slower speed, tease out the very rapid movements and figure out what’s going on.

[CLANKING SOUND]

EDWARDS: Look. Here are two that are really ready to go.

SANDERS: Edwards and her students position the moss with its unexploded capsule in front of the camera.

EDWARDS: Okay. We're ready. Lights.

SANDERS: The lights help with filming, and they also hasten the drying process. We wait. And suddenly:

[CLICK]

EDWARDS: Oh, my god I heard it. Did you hear it? Is that cool?

SANDERS: Now, in case you didn’t hear it, here it is again. It’s single sharp click, and it lasts less than a thousandth of a second.

[CLICK]

SANDERS: Okay, one more time. Ready?

[CLICK]

SANDERS: That click is the sound of the capsule lid tearing open. Just before it blows, the air pressure inside the capsule is about the same amount as in the tire of a semi-truck. And when the lid comes off, thousands of bright orange spores are discharged up into the air. Edwards says when they first shoot out, they’re going between 35 and 65 miles an hour. In terms of height, the spores are swirling 75 times higher than the capsule itself.

And Edwards says for sphagnum, that’s the main advantage. In a natural setting, these exploding capsules allow the moss to get its dust-like spores high enough above the ground so that they’re picked up, and carried away, long distances, by the air currents. If all goes well, some of those spores will land in another suitable habitat where they’ll germinate. Edwards looks at the instant replay of the last explosion.

EDWARDS: Oh wow. Oh beautiful, and this is at 1,000 frames per second? Okay, that's good. Very good.

SANDERS: By analyzing the high-speed video, Edwards and a physicist colleague from Pomona College in southern California discovered that the explosion actually takes the form of a vortex ring and slowed down, looks a lot like a smoke ring. Although jellyfish, squid, and dolphins are all known to make vortex rings, this, Edwards says, is the first report of a vortex ring generated by a plant. For Living on Earth, I’m Laurie Sanders.

GELLERMAN: To see a video clip of exploding Sphagnum capsules, pop over to our website, LOE dot org.

 

Links

Joan Edwards website

Check out this movie! Filmed at only 250fps. You can see the vortex ring shoot upwards like a bright bullet with lots of orange spores flinging off to the sides in whirls. (Courtesy of Joan Edwards)

To see additional videos of exploding sphagnum moss capsules, go to this page and click on individual movie files.

 

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