Development of the pistillate flower of Populus tremuloides following controlled pollination

Quaking aspen branches bearing female inflorescences were forced, artificially pollinated, and grown in water in the laboratory at 25 °C. The pistillate flowers developed normally to produce normal seeds in about 2 weeks. Sectioned material, which had been fixed at different times before and after pollination, revealed that the megagametophyte was in the four-nucleate stage at receptivity of the stigmas, and that it developed through the stages that Nagaraj (1952) described for natural material. Fertilization probably occurred between 72 and 120 h after pollination. Unfertilized ovules within ovaries containing one or more fertilized ovules developed normally for 1 week after pollination, but they began to degenerate soon thereafter.