Figure 1.

(a) Time course of a gravitropic response of a single wheat seedling placed horizontally (perpendicular to the direction of gravity) at t = 0, and measured at 1 h intervals. (b) Mathematical definitions [6]. The angle θ(s, t) at point s along the organ at time t is defined from the vertical. The parameter s runs along the organ from s = 0 at the base, to s = L at the tip. The tip angle θ(L, t) is the quantity which is conventionally measured in experiments. (Online version in colour.)