Friday, May 22, 2009

Getting a Grip

The colour of a flower is the result of a combination of the floral pigments contained in the petal cells and the optical characteristics of the cells themselves, which is why the colour of flowers in photographs doesn’t always correspond exactly with what the eye sees. The cells walls act like lenses, bending and scattering light rays, producing optical effects that combine with the floral pigment colours to produce unique hues, so even a brick red geranium flower shows a bluish tinge from certain angles (bottom picture). These photos show the cells on the surface of a geranium (Pelargonium) petal, which in surface view look like a patchwork blanket, with the patches stitched together (second picture from bottom x100). A side-on view reveals that each cell is actually shaped like a small hill, and that the ‘stitches’ are really pleats (third picture from bottom x100 and fourth picture from bottom x200). The conical cells are typical of many petal surfaces of flowers visited by insects. So why are they this shape? Their lens-like properties contribute to flower colours but their shape and surface texture seems to have evolved to give the claws of pollinating insects like bees (top picture x100) something to grip. By the clever use of mutant forms of snapdragon that have flat, smooth petal surface cells rather than conical ones, Dr. Beverley Glover at Cambridge University’s Department of Plant Sciences has shown that bees avoid smooth petal surfaces because it’s difficult for their claws to grip them and gain enough purchase to force their tongues into the flower. So ultimately it’s the necessity of giving insects a foothold that has produced petal cells with optical properties that add complexity and subtlety to flower colours. There's more about Dr. Glover's research in this web site


  1. Interesting what you say about colour differences between eye and photograph as I was trying to photograph some flowers the other day and the pictures were a completely different colour whereas other flowers next to them came out the true colour. I was completely at a loss as to what was happening.

    Fantastic detailed photos. Thanks for the description. Leaves and stems are often written about but I have not seen this sort of detailed description about petals before.

  2. Thanks John,I think the colour of flowers like bluebells are difficult to record accurately because of the combined effect of petal surface optics and floral pigments - the colour recorded depends on the angle that the flowers are lit from. I've found that petals with hairy surfaces also distort colour rendition, especially if you're using flash.

  3. Fascinating stuff. It really does look like patchwork. Thank you.

  4. Hi Toffeeapple, the cells on plant surfaces do make fascinating patterns. There are some that look like jigsaw puzzle pieces - I'll try to find some.....


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