For this project, we developed a responsive surface based on the behaviors exhibited by the oxalis plant that we had studied earlier: the ability to change shape in response to light levels; clustering to reduce the number of actuators; and the repetition of a single auxetic form that could expand or contract to minimize or maximize exposure to light.
A form finding study using a tensile diagrid mesh of elastic cords. The deformation of the grid and its implied surface are recorded from three views as vertices of the mesh are pulled towards the base.
The Oxalis Triangularis is a great example of a plant that exhibits photonastic behaviour, that is one that produces a mechanical response to changes in light levels. As opposed to (photo)tropic movements which require direct light, nastic responses are due to changes in diffuse levels.
The reaction is made possible by changes in the osmotic potential of cells of the pulvinus at the base of the leaf, a chemo-mechanical process. In addition, the plant also exhibits interesting growth behavior in the formation of the canopy; the larger leafs occurring at the top of the canopy, but organised in such a way that they allow light penetration to the smaller leaves below.
"In tropical jungles, with their great variety of species… We find thin trunks joining into bundles, supporting each other and forming an upward winding spiral. Obviously, the plants compete for the light at the top by sophisticated technical means." (Tributsch 1984:29)