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Ryan T. McWilliams

Project Topic / Abstract:

“Aerodynamic Implications of Saccate Pollen”

Pollen grains of many wind-pollinated plants have one to three air-filled sacci; these add considerable surface area, but minimal weight. With a greater surface area to the wind at a similar mass, it is thought – although not documented – that sacci confer greater flight range to the pollen grain. Using electron microscopy, structurally different saccate pollen grains of three extant conifers (Pinus, Falcatifolium, and Dacrydium) have been examined. Several characteristics have been documented, including overall size, main body size, saccus size, surface ornamentation, wall thickness, wall infrastructure, saccus infrastructure, overall mass, and wall mass. These have been incorporated into a custom computer model programmed in C that calculates flight properties for the theoretical grains based entirely on structural data. The computer model has been tested by stroboscopic photography of actual Pinus pollen. Using this model, structural data can be incorporated from fossil pollen to predict how grains may have flown. As such, the model has been used to aerodynamically evaluate two fossil grains, including the monosaccate pollen of Gothania (Cordaitales) and the small, bisaccate grains of Caytonanthus (Caytoniales). Although recent studies indicate that sacci have a buoyancy function once grains reach a pollination drop in some extant conifers, the present study provides the opportunity to further evaluate the adaptive significance of saccate pollen by correlating structural and aerodynamic features.


  • Schwendemann, A. B., G. Wang, M. L. Mertz, R. T. McWilliams, S. L. Thatcher, and J. M. Osborn.  2007.  Aerodynamics of saccate pollen and its implications for wind pollination. American Journal of Botany 94: 1371-1381. Article (PDF)



  • Truman Undergraduate Research Symposium (Kirksville, MO)


  • Missouri Academy of Science (St. Joseph, MO)
  • Truman Undergraduate Research Symposium (Kirksville, MO)


  • National Conference on Undergraduate Research (Rochester, NY)
  • Sigma Xi Student Research Symposium (Kirksville, MO)
  • Truman Undergraduate Research Symposium (Kirksville, MO)
  • Undergraduate Research Poster Day at the State Capital (Jefferson City, MO)
  • International Botanical Congress (St. Louis, MO)