The nature of the selective pressures which have resulted in the conic
al-papillate shape of the cells of the adaxial epidermis of many petal
s has been a matter for considerable speculation. One suggestion is th
at this shape focuses light within epidermal cells resulting in an inc
rease in the amount of light absorbed by the floral pigments, intensif
ying the colour of the petals and possibly enhancing their attractiven
ess to potential pollinators; another is that conical cells aid pollin
ator orientation on the flower, either visually or when touched. The r
ecent identification of a mutation at the MIXTA locus of Antirrhinum m
ajus (which blocks the formation of conical petal cells) has allowed u
s to test this hypothesis. We report the results of field experiments
indicating that, where pollinator number limits seed-set, flowers with
conical epidermal cells receive more pollinator attention than do tho
se with flat cells. Through the use of double mutants we have examined
whether preferences for flowers with conical cells operate through th
e perception of flavonoid pigments. We have also examined the appearan
ce of flowers with and without conical cells under ultraviolet light t
o determine whether differences in absorption or reflectance of light
at these wavelengths may influence pollinator preference.