## Spirals in Plants? |

**Christophe Golé**

Smith College

May 3, 2010

4:30 pm

Bailey Hall 207

Refreshments will be served in Bailey 204 at 4:15

Many plants exhibit spirals or helices in the arrangement of their organs: leaves around a stem, seeds of a sunflower head, scales in a pine cone or pineapple. These spirals come in pairs of families, and the corresponding numbers of elements in the two families usually are consecutive Fibonacci numbers. We look at a simple geometric and dynamical model consisting of stacking disks one by one on the surface of a cylinder. Given natural assumptions, the system reproduces the known patterns and explains the predominance of Fibonacci numbers. It also gives rise to mathematical structures not mentioned in the mathematical literature: the spirals are not so perfect after all...

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