Experimental phyllotactic patterns in the wake of radially moving chemical precipitation fronts.

In botany, phyllotactic structures are typically regular, spiraled arrangements of leaves, flowers, or other plant organs that grow around a stem. Phyllotactic-like patterns can also be obtained when a reactant of a precipitation reaction is radially injected at a given flow rate in a confined geometry containing the other reactant. Here, we analyze the properties of such spiraled precipitation patterns produced experimentally in the wake of a radially moving reaction front. Specifically, we inject an aqueous solution of sodium carbonate into a solution of barium chloride, or vice versa, and analyze the symmetries of the barium carbonate precipitation patterns. We find that, in a given zone of the parameter space, phyllotactic structures are reproducibly observed. The number of parastichies constructing the symmetry of the pattern varies with injection flow rate, concentrations of the reactant solutions, and buoyancy.