Latitudinal differences in coconut foliar spiral direction: A re-evaluation and hypothesis

Abstract

Davis and Davis (Mathematical Modelling 8: 730-733, 1987) have previously concluded, based on data collected from 42 locations around the world, that the ratio of right-handed to left-handed palm trees (Cocos nucifera L.) exhibits hemispheric differences: left-handed palms are in the majority in the Northern Hemisphere, and right-handed palms are in the majority in the Southern Hemisphere. Weighted and unweighted linear regression analyses of their data reveal that the skewing quotient [(left-handed-right-handed)/total] is better correlated with magnetic (dip) latitude than with geographic or geomagnetic (centred dipole) latitude. The hypothesis is advanced that latitude-dependent biases in foliar spiral direction may be associated with the temporally varying component of the earth's magnetic field. It is known that changes in the current strength of the ionospheric dynamo induce clockwise earth currents in the Northern Hemisphere and counterclockwise earth currents in the Southern Hemisphere. The hypothesis is advanced that these earth currents, which are measurable in trees, bias the diffusion of auxin (or auxin transport proteins) in young embryos such that left-handed trees are produced preferentially in the Northern Hemisphere and right-handed in the Southern Hemisphere. Some tests of the induced Current Hypothesis are proposed.