Deegan group

Impatiens seed pod

Mechanics of seed pod explosion

Many plants spread their seeds by throwing them.  This is accomplished by a slow build up of elastic energy which is then rapidly released to accelerate the seeds.  A rapid release requires a trigger mechanism.  A widespread strategy is to rupture the bonds that contain the stored energy with a crack.  Cracks are indeed fast, but they are very costly in energy because the crack tip consumes energy to pay for the newly created surfaces.  My research on this subject was motivated by seemingly contradictory result that practical all the stored energy is transfered to the seeds. The resolution to this puzzle is found in the tapered construction of the seedpod.


R. D. Deegan, "Finessing the fracture energy barrier in ballistic
seed dispersa
l", Proceedings of the National Academy of Science (2012).