TRANSITION FROM A UNIFORM STATE TO HEXAGONAL AND STRIPED TURING PATTERNS

CHEMICAL travelling waves have been studied experimentally for more than two decades 1-5, but the stationary patterns predicted by Turing 6 in 1952 were observed only recently 7-9, as patterns localized along a band in a gel reactor containing a concentration gradient in reagents. The observations are consistent with a mathematical model for their geometry of reactor 10 (see also ref. 11). Here we report the observation of extended (quasi-two-dimensional) Turning patterns and of a Turing bifurcation-a transition, as a control parameter is varied, from a spatially uniform state to a patterned state. These patterns form spontaneously in a thin disc-shaped gel in contact with a reservoir of reagents of the chlorite-iodide-malonic acid reaction 12. Figure 1 shows examples of the hexagonal, striped and mixed patterns that can occur. Turing patterns have similarities to hydrodynamic patterns (see, for example, ref. 13), but are of particular interest because they possess an intrinsic wavelength and have a possible relationship to biological patterns 14-17.