Gerard, John (1597). Herball, or Generall Historie of Plantes. London: John Norton. pp. 612–614. Retrieved 2012-08-08. Popular botany book in 17th century England.
"When the plant is in the bud stage, it tends to track the movement of the sun across the horizon. Once the flower opens into the radiance of yellow petals, it faces east." National Sunflower Association http://www.sunflowernsa.com/all-about/faq/#11
