Here's an animation that runs in recent Chrome, Firefox and Safari at least: http://www.mac-guyver.com/switham/2014/02/Meristem/ There's are links there to a set of 3 Vi Hart videos about spirals in plants, S. Douady and Y. Couder's magnetized oil drop experiment video, and  "The Mathematical Lives of Plants," by Julie J. Rehmeyer.  --Steve