Metallic lustre and the optical mechanism generated from the leaf surface of Begonia rex Putz.

The mechanism of sparkling metallic lustre formation in leaves of Begonia rex Putz. was investigated. On the metallic lustre and normal green areas of one leaf, we observed two light reflection patterns, one a spotted pattern (SP) composed of white spots formed on the centre of epidermal cells and the other a polygonal pattern (PP) composed of white polygons formed around the epidermal cell edges. The SP was observed both in metallic lustre and normal green areas, and the intensity did not differ significantly, but the PP was much stronger in the metallic lustre area. Different reflection of the PP in metallic lustre and normal green areas indicated that metallic lustre formation was attributable to the PP. Light reflection of the PP was mainly derived from interior light reflection because the PP became very weak after air removal from leaf. The formation of the PP is associated with the interior structure of the leaf, such as chlorophyll density, cell arrangement and air space. The experimental results indicated that interior air space is an important factor in forming the polygonal pattern.