Botanical Ratchets

TL;DR

This paper demonstrates that natural ratcheting surfaces like grass awns act as motion rectifiers, converting environmental stresses into directed motion, with efficiency proportional to their length, providing a selective advantage in seed dispersal.

Contribution

It introduces a combined theoretical and experimental analysis showing how plant awns function as natural ratchets, enhancing seed dispersal through unidirectional motion under symmetric stimuli.

Findings

Awn length correlates linearly with ratchet efficiency.

Grass awns convert environmental stresses into useful work.

Natural ratchets provide a selective advantage in seed dispersal.

Abstract

Ratcheting surfaces are a common motif in nature and appear in plant awns and grasses. They are known to profer selective advantages for seed dispersion and burial. In two simple model experiments we show that these anisotropically toothed surfaces naturally serve as motion rectifiers and generically move in a unidirectional manner when subjected to temporally and spatially symmetric excitations of various origins. Using a combination of theory and experiment we show that a linear relation between awn length and ratchet efficiency holds under biologically relevant conditions. Thus, grass awns efficiently transform non-equilibrium environmental stresses into useful work and directed motion using their length as a fluctuation amplifier, yielding a selective advantage to these organelles in many plant species.