Observations on ultraviolet-fluorescent trichomes on the tepals of narcissus flowers

Abstract

When the flowers of Narcissus tazetta, which are white with an orange corona, were observed under ultraviolet light, the tip of each tepal showed blue fluorescence while the rest of the tepal absorbed ultraviolet light and appeared dark brown. In double flowers the tips of the perianth segments derived from stamens also showed a blue fluorescence. The fluorescence was found to be due to the presence of a tuft of trichomes at the subapical part of the tepals. The trichomes arise from a stalk-like cushion on the adaxial surface of the subapical part of the tepal. Each trichome is initiated as a protuberane from an epidermal cell which by cell division develops into a multicellular and uniseriate structure, consisting of a single row of 3–6 cylindrical cells. Most cells have a loose net-work of cuticular folds or ridges on their walls. The probable nature of the fluorescent compounds in the trichomes and the possible function of these trichomes as insect guides in pollination of the flowers of N. tazetta are discussed.