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Daniel H. Janzen

Abstract

The movements of the styles (and consequently stigmas) of flowers of Central American Passifloraceae is described. The timing of this behavior is closely associated with the timing of flower visitors and pollinators; the result is that the first pollinators to arrive visit many flowers and can contact only anthers. Later, the styles bend over and these same insects place a mixture of pollen from many flowers on the stigmas, rather than a coat of pollen from the same flower as would have been the case had the styles been bent over from the time of flower opening. The flowers pollinated by hummingbirds (flying all day) are much slower to turn down their stigmas than are the species pollinated by early morning bees with a short flight period. It is postulated that the selective forces that have led to the timing and movements of the styles and stigmas are those positive advantages generally associated with out-crossing in plants.