This video clip shows the dispersal of spores from the leptosporangia of a tree fern, Cyathea cooperi.
The leptosporangia have specialized cells, collectively known as the annulus, which have thickenings in the
radial and inner tangential walls. As the sporgangia dry out, the annular cells shrink, but primarily on the outer tangential wall,
where the cell walls are thin. This shrinkage, caused by polar water molecules attracting one another and adhering to the cell wall, results in
the annulus breaking and pulling away from the sporangium body. As the linear body of the annulus pulls away, it encompasses spores from the
sporangium body. After a short period of time, the water within the annulus evaporates completely, the tensile force is lost, and the annulus
snaps back, catapulting the spores into the air.