  The carnivorous aquatic Waterwheel Plant (Aldrovanda vesiculosa L.) and the
closely related terrestrial Venus Flytrap (Dionaea muscipula SOL. EX J. ELLIS)
both feature elaborate snap-traps, which shut after reception of an external
mechanical stimulus by prey animals. Although Aldrovanda is usually considered
as a miniature aquatic Dionaea, the shutting mechanisms of the two plants are
actually quite different. The fast shutting of Aldrovanda is indeed based on a
simple swelling/shrinking mechanism, while the movement of Dionaea's traps is
accelerated by the snap-buckling of the lobes. The purpose of this Report is to
describe several key improvements to the elastic models that have recently been
introduced to elucidate these movements [Poppinga and Joyeux, Phys. Rev. E 84,
041928 (2011)]. In particular, a precise mechanism for the action of the motor
cells of Aldrovanda is proposed, the facts that the opening of the leaves of
Dionaea is an irreversible mechanism based on growth and that the strain field
is anisotropic and much smaller on the inner than on the outer surface of the
leaves during shutting are taken properly into account, and a more accurate
formula for calculating mean curvatures is used. The improvements brought to
the model are described in detail and the physical consequences of these
improvements are discussed.
