From Science, May 27, 2005, an intriguing article on “Physical Limits and Design Principles for Plant and Fungal Movements” (Jan M. Skotheim, L. Mahadevan). Most plants move slowly; some move swiftly – Hura crepitans shoots out seeds at up to 70 m/s, Venus flytrap catches insects in ca 0.2 s, and the fungus Dactylara brochopaga swells to trap nematodes in 0.1 s. Other examples of quick-moving plants: the fungus Philobulus, Catasetum orchids and Stylidium triggerplants, Mimosa. The plants exploit the large internal pressure (turgor) that having a cell wall allows them to have, and motion is determined by the rate of fluid transport. The authors publish a colorful plot of time scale versus the smallest macroscopic dimension of the moving part, and group the types of movements into swelling/shrinking (durtion limited by fluid transport), snap-buckling, and explosive fracture, the latter two being a result of elastic instabilities. The biggest, fastest movements are made by Hura crepitans, and Eclallium elaterium – if I’m reading the colours on the chart right, and they’re less than 10 mm in 0.001 – 0.0001 s, which alas means all our favourite big nasty plants fall in the section of the plot marked “Physically impossible movements”, at least if they’re restricted to using water pressure. The authors contrast the Venus flytrap (0.2 s) and Aldrovanda (0.02 s): an Aldrovanda leaf is about 1/10th the size of a Venus flytrap leaf, which should translate to about 100 times the speed, but the design of the Venus flytrap leaf includes a reversal of curvature and a snap. If you want to see pictures, then the (unrelated) site Plants in Motion has Quick Time movies of a Venus flytrap closing, and a Mimosa leaf curling up like a blind when the tip is warmed.