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Circumnutation is an oscillating movement of a growing plant organ that results from an endogenous rhythmic process intrinsic to growth. Circumnutating organs, as they extend, describe a helical trace. In Arabidopsis thaliana circumnutation is particularly evident in primary roots and occurs, as in most plants, in a right-handed direction. In A. thaliana the direction of circumnutation depends on the presence of a single gene with the right-handed allele dominant over the left -handed, as in Zea mays where again a single gene controls the left or right spiralization of the kernels on the ear. Furthermore we demonstrate that the specification of the left/right asymmetry is dependent on the establishement of the antero-posterior axis on the ear.