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In petals of various species of angiosperms that differ in ultraviolet absorption and reflectance, flavonoids were concentrated at surfaces that absorb ultraviolet light. Microscopic examination of intact, dried petals treated with sodium methoxide revealed dense concentrations of flavonoid material in the tips of specialized epidermal papillae. Scanning electron micrographs confirmed this cellular localization and disclosed structural features of the cuticle which are associated with ultraviolet absorption. These papillate epidermal cells have an adaptive complex of chemical and structural features which function in ultraviolet absorbance patterning on the surfaces of flower petals and assist in visual discrimination by insects.
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Brehm et al. (1975) studied this question.
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