Studies on flower longevity in Digitalis : Pollination induced corolla abscission in Digitalis flowers.

Flower lifespan was terminated by corolla abscission 5-6 days after stigma opening in the unpollinated flower. Increased pollen loads produced increased seed set and reduced flower longevity progressively to a minimum of one day after pollination with pure pollen. Weakening of the abscission zone was detectable 8 h after pollination, whilst the pollen tubes were still within the stigmatic zone, suggesting that a stimulus, moving at 4 mm h(-1) minimum, was transmitted through the style and ovary. Soon after pollination removal of the stigma prevented the pollination-induced corolla abscission. Later it was necessary to remove the stigma and upper style, and later still the whole style to delay abscission. The progressive induction of the stigma and style took place at a rate of 1.5 mm h(-1), in advance of the pollen tubes which grew at 0.75 mm h(-1). It was not possible to reproduce the pollination effects by application of indoleacetic acid (IAA) to the stigma or the style.