Lever action anthers and the forcible shedding of pollen in Torenia (Scrophulariaceae)

The anthers of Torenia fournieri were found to shed pollen forcibly by lever action. Anther structure was modified for this function by a flangelike outgrowth of the lateral pollen sac wall forming a lever. When pressed, this lever causes an infolding of the thinner, subadjacent, pollen sac wall forcing pollen from the stomium. A force of 1-1.5 g pressing against the four levers of an anther pair resulted in the forcible shedding of 2,000-3,000 pollen grains in two parallel rows. During the 2-day anthesis the flowers shift from functioning as males to hermaphroditic outcrossers, and yet only have a pollen: ovule ratio of 98.6, a ratio more indicative of facultative autogamy. The outermost pair of anthers functions on the first day of anthesis, while the second, inner pair functions on both days. In each flower, the 2-day anther pair produces approximately twice as many pollen grains as the 1-day anther pair, a pollen production highly correlated with the length of their functional lives. This difference in pollen production is apparent in the larger size of the 2-day anthers, a size difference that first appears with the initiation of the anther primordia.