I've long known that jewelweed (Impatiens capensis) aka "touch-me-not" does ballistic seed dispersal--probably giving it its other common name. But I'd never paid enough attention to look for the plant when it had fruit. On a walk around Ponkapoag Pond during the annual August stay at our AMC Ponkapoag cabin, I finally took a look. Finding some with mature pods, I reached out to pick a pod for a closer look and was surprised when it squirmed weirdly in my hand and transformed into what looked like tiny springs!
Fascinated, I sought out more pods and experimented. I soon found I could trigger the pods at will, but the action is too fast for the human eye.
The little "springs" begins as a straight ribs that runs the length of the pod. Water pressure inside the cells of this spring tries to bend it into its coil shape, but the rest of the pod just barely restrains it. Anything that begins the rupture of the pod pushes this delicate balance over the edge, and the ribs coil very quickly, tearing the pod and flinging the three seeds in the process. The seeds may only travel a few inches, but this might be enough, so that the next generation gets its start in more open soil and perhaps away from Momma's shade.
Since most mature plants cannot move on their own, methods of dispersal are important for spreading offspring far enough to give at least a few a fighting chance at survival.
Plants have a variety of ways of accomplishing this dispersal. Many produce tasty fruit that attract the attention of mammals and birds: these carry the seeds some distance and even "plant" them in a little packet of fertilizer. (Did you imagine that plants made fruit for our benefit??) Others are built to be dispersed by wind (think dandelions or milkweed). Some, such as stick-tights and burs of various sorts, have hooks that allow them to hitch a ride on the fur of animals--the original Velcro. (Their catching annoyingly in your socks or sweater is a modern accident.) A few appear unaccountably unable to disperse. Osage orange has a large, tough fruit that is not eaten by any animal--but probably was once food for large herbivores that are now extinct.
By the way, the stems of jewelweed are reputed to be good for preventing or reducing the rash that can come from contact from poison ivy. If you think you've touched poison ivy, you can grab some stems of jewelweed and crush them and rub the juice on your skin. Can't hurt. Of course, you won't necessarily get a rash from casual contact with poison ivy, anyway--I have brushed by it many times with no ill effect, even though I am pretty allergic.
First try.
Fascinated, I sought out more pods and experimented. I soon found I could trigger the pods at will, but the action is too fast for the human eye.
How fast? Try to follow the motion.
The little "springs" begins as a straight ribs that runs the length of the pod. Water pressure inside the cells of this spring tries to bend it into its coil shape, but the rest of the pod just barely restrains it. Anything that begins the rupture of the pod pushes this delicate balance over the edge, and the ribs coil very quickly, tearing the pod and flinging the three seeds in the process. The seeds may only travel a few inches, but this might be enough, so that the next generation gets its start in more open soil and perhaps away from Momma's shade.
Since most mature plants cannot move on their own, methods of dispersal are important for spreading offspring far enough to give at least a few a fighting chance at survival.
Plants have a variety of ways of accomplishing this dispersal. Many produce tasty fruit that attract the attention of mammals and birds: these carry the seeds some distance and even "plant" them in a little packet of fertilizer. (Did you imagine that plants made fruit for our benefit??) Others are built to be dispersed by wind (think dandelions or milkweed). Some, such as stick-tights and burs of various sorts, have hooks that allow them to hitch a ride on the fur of animals--the original Velcro. (Their catching annoyingly in your socks or sweater is a modern accident.) A few appear unaccountably unable to disperse. Osage orange has a large, tough fruit that is not eaten by any animal--but probably was once food for large herbivores that are now extinct.
Jewelweed with flower and pods.
What remains of the pod after "firing."
By the way, the stems of jewelweed are reputed to be good for preventing or reducing the rash that can come from contact from poison ivy. If you think you've touched poison ivy, you can grab some stems of jewelweed and crush them and rub the juice on your skin. Can't hurt. Of course, you won't necessarily get a rash from casual contact with poison ivy, anyway--I have brushed by it many times with no ill effect, even though I am pretty allergic.
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