3 Mar 2005; Mat-Nat Faculty (UITO), room U4. Thursday  14:15-16:00

Alan Newell (University of Arizona, USA & University of Warwick, UK)

"Plant patterns and plant phyllotaxis"

The polygonal patterns and the arrangement of leaves on plant surfaces such as sunflowers and cacti have intrigued natural scientists since the time of Johannes Kepler. In particular, it is observed that the numbers of arms in the families of spirals on which plant stickers lie are sequential members of Fibonacci sequences with the most common being 1,1,2,3,5,8,13... Moreover as the plant grows, the spiral numbers move up the Fibonacci sequence in a series of second order phase transitions. In this talk I will review several recent attempts to explain these phenomena and offer a new theory which seems to capture most of what is observed including the reason that some plants exhibit phyllotaxis without any connection with Fibonacci at all.

The talk should be accessible to all.