Analysis of the growth rate near the micropyle. (A) The average rate of growth depends on the distance to the micropyle. When pollen tubes grow within 50 μm of functional ovules, they consistently slow their rate of growth, an effect not observed with heat-treated ovules. When pollen tubes approach ovules with a longer incubation time, this slowing occurs at longer distances. (Inset) The growth rates of functional and heat-treated ovules are consistent until pollen tubes grow within 50 μm of a micropyle. (B) The fraction of tubes able to target micropyles in simulations where either the turning response (T) or the slowing response (S) were removed to determine the role each would play in guidance. The set T+S+ (*) indicates simulations were the random growth was kept constant, and did not show a significant difference in targeting compared to T+S+, where the size of the deviations in the random growth varied with the growth rate (). We considered a pollen tube to have targeted (fertilized) an ovule successfully when its tip reached a 10 μm distance from a micropyle. (C) Characteristic paths of tubes at 4-hour incubation times in the T+S- simulations (top) and T+S+ simulations (bottom). The positions of the ovules, and the positions and initial directions of the pollen tubes were taken from the experiment shown in Fig. 2A.