Abstract: There are two premature drop climaxes for Xanthoceras sorbifolia Bge., one in the young fruit period and the other in the fruit expansion period, the dropped fruits amount to 75% and 15% of the total of the female flowers. We determined by gas chromatography the amount of internal ABA in different fruits in the two periods. The result shows that in the young fruit period the amount of ABA in dropped young fruits is 2-9 times higher than the undropped. During the fruit expansion period, the level of ABA in fruits which stopped growing is 1.1-1.8 times higher than normal.Therefore, the high content of ABA in fruits is one of the most important factors leading to the premature drop for Xanthoceras sorbifolia Bge.

Key words: Xanthoceras sorbifolia Bge, premature drop, internal abscisic acid