Pollen tube attraction to ovules. (A) Ovules and the cut stigma (upper left corner) are shown in red. Pollen tubes are shown, emerging from the style, in blue. The white concentric circles depict radial bins of 50, 100, 150, 200 μm around one of the micropyles (central white circle). The tips of the pollen tubes are marked with yellow boxes. Scale bar (white) is 100 μm. (B) Bar chart describing the time-averaged frequency that, at a given distance, the tip of a pollen tube grew closer to (top) or farther from (bottom) the nearest micropyle. The distances are split into radial bins with ΔR = 50 μm (0-50 μm, 50-100 μm, etc.). (C) Depiction of θ
angles used in the analysis of pollen tubes turning. The θ
angle indicates how much the pollen tube would have to turn to take the most direct path toward the micropyle. The θ
angle describes the new direction chosen by the pollen tube in response to the gradient. (D) Circular standard deviations σ0 for distributions of Δθ for points 0-50 μm and 50-100 μm from the closest micropyle for directions where the pollen tube is growing toward the micropyle (cos θ
≥ 0). The key for the bars shown in B and D is the same.