  One of humanity's earliest mathematical inquiries might have involved the
geometric patterns in plants. The arrangement of leaves on a branch, seeds in a
sunflower, and spines on a cactus exhibit repeated spirals, which appear with
an intriguing regularity providing a simple demonstration of mathematically
complex patterns. Surprisingly, the numbers of these spirals are pairs of
Fibonacci numbers consecutive in the series 1, 2, 3, 5, 8, 13, 21, 34, 55...
obeying a simple rule 1+2=3, 2+3=5, 5+8=13 and so on. This article describes
how physics helps to clarify the origin of this fascinating behavior by linking
it to the properties of deformable lattices growing and undergoing structural
rearrangements under stress.
