In many instances, the dynamics of physical systems depends on their history,
for example when retardation effects exist. It is also a dominant feature of growth
problems. For instance, in the case of a radially growing Saffman–Taylor viscous
fingering, the structure of the initial destabilization continues contributing to the
Laplacian field which determines the later growth (Couder 2000). Similarly, the highorder
Fibonacci organization observed in the capitulum of a sunflower is the
product of a sequence of successive bifurcations during the whole plant development
(Douady & Couder 1996). In those cases, the system is open and changes with time.