"Spiral pattern helps cacti deal with stress," by Anil Ananthaswamy. New Scientist, 8 May 2004, page12.
The relationship between the Fibonacci numbers and spirals that appear in plantgrowth is well known. But what causes this relationship? This articlediscusses recent research aimed at answering this question. The researchers,Patrick Shipman and Alan Newell at the University of Arizona, suspected thatthe spirals emerge because of stresses on the growing plant. In a cactus,these stresses cause sets of ridges to appear on the cactus's outer layer,called the tunica. Shipman and Newell developed a mathematical model of cactusgrowth that minimizes these stresses. "The number of ridges in each setfollows a Fibonacci series which according to Shipman and Newell is exactly thepattern predicted by their mathematical model", the article says.
--- Allyn Jackson