In a variety of grass species, awns play a significant role in seed dispersal and burial. It has long been observed that the movement of various awns was controlled by humidity level, where low humidity brings about the contraction of actuating parts in the awn and high humidity causes these parts to relax. The daily cycle of humidity level produces a periodic movement, propelling the attached seed across the ground into safety. We aim to understand the microscopic structures enabling such hygroscopic movement in various awns.

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Dispersal mechanism of stork's bill (Erodium gruinum)

 

We utilize light and electron microscopy, Raman micro-spectroscopy, and X-ray diffraction, to reveal the cellulose fibril orientations within the twisting part of the hygroscopic awn. Fluorescence of the sample, measured in cross sections, together with specific Raman lines, allow us to study the composition of the cell wall matrix.