To compare the results of our model with the observed motion of the stamens, we measured the physical parameters L, d, m, M and k. To determine the mass of the anther (m), we weighed 48 anthers with their pollen from 21 mature flowers (2·0 mg), with an average mass of 0·024 mg. We estimated the uncertainty for this mass by looking at the size variation within a sample. Assuming that the mass of the anthers scales as their length cubed, the fractional uncertainty in mass will be three times the uncertainty in length. Length measurements taken on nine anthers had a standard error of 2%, which corresponds to a statistical uncertainty in mass of ±6%. A still frame from the high-speed video recording was used to determine the sizes of the anther (d) and filament (L) as well as the filament's mass, M. The length of the anther was 0·070 mm, which corresponds to d = 0·035 mm. The length of the upper part of the filament, L, was 0·80 mm with an average diameter of 0·16 mm. The mass of the upper portion of the filament was estimated by assuming that it had the density of water. Assuming cylindrical symmetry, we obtain a mass of 0·016 mg. The filament diameter varies by about ±10% along its length. As the volume of the cylinder depends on this value squared, we assume an uncertainty of ±20% in its mass. Finally, to determine the spring constant k, we measured the force required to re-bend a filament through a known angle. We measured forces (typically ≈10−4 N) by bending a filament against the pan of an electronic balance (model AB104, Mettler Toledo, Greifensee, Switzerland). The restoring torque was determined by measuring the magnitude and position of the force required to hold the filament at a number of known angles. Measurements on three samples gave a restoring torque, Γ, which varied linearly with φ from its equilibrium condition, Γ = –k(φ0 − φ). We found that k = (1·5 ± 0·9) × 10−7 J. The error is based on uncertainties in measuring the contact point of the digital balance and the statistical error of a linear fit to the data. We also measured the force required to keep a filament bent in a flower that had not yet opened, by restraining a single filament with the pan of the electronic balance as a flower was triggered open. This method measured only the force for a single angle, but data taken on two samples gave an average spring constant of k = 1·1 × 10−7 J, which lies within the range of values for already opened flowers. From this we conclude that the elastic properties of the stamens are not significantly affected by the opening process.