the fern leaves sporangia are packed together. These capsules
are full of spores and surrounded by a row of cells: the
annulus. This acts as an elastic beam which opens under
dehydration of the cells contents. The large deformation
induced is coupled to large negative pressures in the cells,
leading at some point to the nucleation of cavitation bubbles.
At this moment, the elastic energy is released, the annulus
closes back very quickly, ejecting the spores. Ancient ages
catapult present a crossbar that would stop the beam motion
midway. Without it, projectiles would have been thrown
directly into the ground.
We discovered that because of the porous nature of the annulus, the fast closing motion takes place in two time scale. The first one is inertial: it lasts a few tens of microsecond. The second one is poroelastic and lasts a few tens of milliseconds. This allows to eject the spores at more than 10 m/s.
See highlights in:
studied the ejection of fungal spores from the basidiomycetes
family. This ejection of spores is induced by fast capillary
action due to droplet coalescence.
The Journal of Experimental Biology's Outstanding paper prize 2009
|We have studied simple microfluidic devices mimicking leaves to better understand the geometric relationships between vein spacing and leaf thickness and their effect on transpiration. We have then measured the same paramters in real leaves, and observed the same scalings, showing the strong correlation between the thickness of a leaf and the minimal spacing bteween its veins.|