CONIFER OVULATE CONE MORPHOLOGY: IMPLICATIONS ON POLLEN IMPACTION PATTERNS

Abstract

Empirically determined patterns of pollen impaction on the surfaces of pine ovulate cones are correlated with regions of nonlaminar flow created by the spatial arrangement and morphology (aspect ratios) of scale‐bract complexes. Results from the serial discharge of pollen, upwind of ovulate cones, indicate that ovules on ovulate cones are preferentially impacted by pollen from their own species. Analyses indicate that while aerodynamic factors dominate the entrapment of pollen by ovulate cones, other factors such as pollen impaction‐rebound and rebound‐reentrainment are significant. Surface characteristics in addition to the settling velocities of pollen may play important roles in determining pollination efficiency. Wind tunnel analyses of the aerodynamic effects of scale‐bract arrangement and aspect ratios indicate that each complex behaves as an aerofoil, deflecting air eddies toward the micropylar ends of ovules. The ovulate cone geometry, as a whole, deflects unidirectional wind into cyclonic vortices around the cone axis, each scale‐bract deflecting nonimpacted pollen along orthostichies and parastichies. The morphology of the typical conifer ovulate cone is interpreted as a structure that optimizes anemophilous reproduction.