Annulus All Bent Out of Shape

i-0d86b5f4ebead46240388125018ea756-2544474516_b572a84a43-thumb-500x375-73426.jpg
Fern Roof (Kathrin Marks)

Imagine that you're a spore nestled on a leaf in a sleepy forest. It's a dry, sunny day. All of a sudden - within 0.00001 seconds, you are flung into the air with an acceleration of 100,000 times the force of gravity. What happened?

The play by play of this extraordinary voyage is now explained:

The whole annulus is thus bent out of shape, much like an accordion in the hands of a musician.

The sporangia open when dehydrating and use the stored elastic energy to power a fast closure motion that ultimately ejects the spores. The beauty of this dispersal mechanism and its similarity with medieval catapults have not escaped notice (1). All man-made catapults are equipped with a crossbar to stop the motion of the arm midway. Without it, catapults would launch their projectiles into the ground. This crossbar is conspicuously missing from the sporangium, suggesting that it should simply speed up to its closed conformation without ejecting the spores. We show that much of the sophistication of this ejection mechanism and the basis for its efficiency lie in the two very different time scales associated with the sporangium closure.

It's as if inside each fern is a spore sack mimicking a medieval catapult (or is it the catapult mimicking the spore?) to launch each spore with maximum velocity to begin the next generation.

A dozen cells placed in a row can fulfill all the functions of a medieval catapult, including the motive force for charging the catapult (water cohesion), energy storage (annulus wall), triggering mechanism (cavitation), and returning motion arrest (poroelastic behavior of the annulus wall).

Pretty clever!

More like this

I recently saw a comment on a blog somewhere about putting satellites into space (I think it was from a post about a rocket that blew up). The poster suggested using a giant catapult to put things in space instead of rockets. Maybe he or she was kidding, or maybe not.
Is this video a deplorable example of cruelty to animals, or an entertaining way of dealing with bushy-tailed vermin?
Elizabeth Edwards -- who catapulted into the public eye in 2004, when her husband, Sen. John Edwards, ran for president and was John Kerry's running mate on the Democratic ticket, has died, a close family friend tells NPR. She was 61.

A tiny nitpick; ferns have fronds, not leaves. See how warped my mind is from being a TA in freshman botany labs some 50 years ago. ;-)

By Jim Thomerson (not verified) on 09 Apr 2012 #permalink