Schematic representation of the custom-designed experimental unit (not in scale).

Abstract

<p>(<b>a</b>) The seal at the base of the central cylindrical box ensured that chilli seeds arranged in a circle around the adult plant were chemically isolated from it. (<b>b</b>) All seeds and adult plants within a replicate unit were housed within 2 different sized square boxes, one inside the other, with the air in between the two boxes removed using a vacuum pump. The whole experimental unit was custom-made in colourless cast acrylic material (ModenGlas), which transmitted 92% of visible light, but was opaque to ultraviolet and infrared wavelengths.</p