Fig. 1

Fruit set (mean ± SE) at 10 and 30 days after inter- and intraspecific hand pollination in the ancient and recent secondary contact zone between Quercus liaotungensis and Q. mongolica. The open and solid circles represent fruit set after inter- and intraspecific pollination, respectively. Figures a and b indicate the fruit set at 10 and 30 days after pollination when Q. liaotungensis comprised the maternal plants, respectively, and the Figures c and d indicate the fruit set at 10 and 30 days after pollination when Q. mongolica comprised the maternal plants, respectively