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Demonstration of the hinge mechanism and internal structure of the galea of Pterostylis sanguinea. (A) Flower with the hinge ready to trap a pollinator. (B) The labellum has triggered and moved into the ‘up’ position and the column wing has been removed to show the passage through which the gnat must move to exit the flower. The flower is approximately 10 mm across the galea. Photographs by K. W. Dixon.
