Summer Flower
by Beverley Harper Tinsley
Title
Summer Flower
Artist
Beverley Harper Tinsley
Medium
Painting - Watercolor
Description
A single sunflower glows on a cool background.When I was a kid, I always knew I'd grow up to be the kind of adult who grows sunflowers.
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Sunflower (Helianthus annuus) is an annual plant native to the Americas. It possesses a large inflorescence (flowering head), and its name is derived from the flower's shape and image, which is often used to depict the sun. The plant has a rough, hairy stem, broad, coarsely toothed, rough leaves and circular heads of flowers. The heads consist of many individual flowers which mature into seeds, often in the hundreds, on a receptacle base. From the Americas, sunflower seeds were brought to Europe in the 16th century, where, along with sunflower oil, they became a widespread cooking ingredient. Leaves of the sunflower can be used as cattle feed, while the stems contain a fibre which may be used in paper production.
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A common misconception is that flowering sunflower heads track the Sun across the sky. Although immature flower buds exhibit this behaviour, the mature flowering heads point in a fixed (and typically easterly) direction throughout the day. This old misconception was disputed in 1597 by the English botanist John Gerard, who grew sunflowers in his famous herbal garden: "[some] have reported it to turn with the Sun, the which I could never observe, although I have endeavored to find out the truth of it." The uniform alignment of sunflower heads in a field might give some people the false impression that the flowers are tracking the sun.
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The uniform alignment results from heliotropism in an earlier development stage, the bud stage, before the appearance of flower heads (anthesis). The buds are heliotropic until the end of the bud stage, and finally face East. Their heliotropic motion is a circadian rhythm, synchronized by the sun, which continues if the sun disappears on cloudy days. If a sunflower plant in the bud stage is rotated 180�, the bud will be turning away from the sun for a few days, as resynchronization by the sun takes time. The heliotropic motion of the bud is performed by the pulvinus, a flexible segment just below the bud, due to reversible changes in turgor pressure, which occurs without growth.
Uploaded
March 19th, 2013
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