POLLEN CAPTURE AND WIND-INDUCED MOVEMENT OF COMPACT AND DIFFUSE GRASS PANICLES: IMPLICATIONS FOR POLLINATION EFFICIENCY

The motion induced by wind of Setaria geniculate (Lam.) Beauv. and Agrostis hiemalis (Walt.) B.S.P. panicles is shown to have harmonic characteristics that can influence pollination. During each cycle of its motion, the panicle of S. geniculata repeats a sequence of reorientations to the direction of ambient airflow. This repetition is correlated with a reiteration of airflow patterns through which airborne pollen grains must pass to reach floral surfaces. The panicle decelerates as it moves toward either of the two extreme positions of its oscillatory motion. The decelerations introduce a bias in the time the panicle spends in each of its orientations. This bias generates “preferred orientations” to the direction of ambient airflow which in turn results in biasing the aerodynamics of pollen capture. Similar phenomena are reported for the panicle of A. hiemalis, although a more complex pattern of oscillatory motion is observed. The reciprocity between the mechanics of oscillatory motion and the aerodynamics of pollen capture is shown to have deterministic properties which may surface above the “noise” produced by other, stochastic features influencing wind pollination.