The column of the trigger plant, Stylidium graminifolium, when fully set responds to mechanical
stimuli by flipping through an angle of about 4 radians in a fast firing movement lasting about
15-30 ms, and then slowly resetting to its original position in about 400 s. After resetting there is an
absolute refractory period of about 500 s during which no further response to stimuli can be initiated,
followed by a relative refractory period when graded responses increasing in rate and magnitude
with time can be obtained. The resetting movement and the process, occurring during the refractory
period, allowing subsequent firing to occur, are inhibited when the air surrounding the column is
replaced by nitrogen. The firing movement, however, is not affected by these anaerobic conditions.
Thus the firing movement is caused by passive physical forces, rapidly utilizing potential energy
from a store built up during the previous resetting and refractory periods. Removal of the labellum,
which the column touches when set, causes the column to oscillate with amplitude of about 3-3.5
radians and period of 1-2 ks. When the column is held at a constant angular displacement it develops
an oscillatory torque with similar period. These oscillations are inhibited at all stages of the cycle
by anaerobic conditions. It appears that the oscillatory behaviour is not a slowed-down firing process
followed by normal resetting, but is linked throughout the cycle to the metabolic energy supply.