Shooting Mechanisms in Nature: A Systematic Review
Fig 20
Cavitation catapult mechanism in the family Polypodiaceae or common ferns.
(A) The mature sporangium in common ferns consisting of a stalk and an annulus enclosing the spores. (B) Dehydration of the annulus cells causes the radial cell walls to come closer together and the lateral walls to collapse internally, straightening the annulus. (C) When a critical pressure (between -9 and -20 MPa relative to ambient) is reached, cavitation occurs in the cells of the annulus. (D) Discharge of the spores by quick release of the elastic energy stored in the cell walls as the annulus snaps back to its original shape. Drawings based on high-speed images in [94]. Scale bar 0.2 mm (200 μm).