Pink cranesbill, Pelargonium zonale

Pink cranesbill, Pelargonium zonale

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This image is part of the feature Dalton's Eyeballs: A Mystery Solved

Credit: JAMES KING-HOLMES/SCIENCE PHOTO LIBRARY

Caption: Cranesbill. The pink flower of a cranesbill plant, Pelargonium zonale. The colour-blind English chemist John Dalton (1766-1844) saw these pink flowers as "sky-blue" by daylight, but "very near yellow, but with a tincture of red" by candlelight. The first scientist to give a detailed description of colour blindness, Dalton believed the fluid in his eyes was tinted blue. To test the theory he asked a physician to cut open his eyes after his death and examine the contents. Dalton proved to be wrong, but the eyes were preserved, allowing 20th-century scientists to extract Dalton's DNA and identify the mutant gene responsible for his colour blindness.

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Keywords: botany, colour blindness, colour deficiency, cranesbill, daltonism, flower, flowering, flowers, geranium zonale, nature, pelargonium zonale, pink flower, plant, plants

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