Confocal Microscopy Image Gallery
Plant Tissue Autofluorescence Gallery
Sunflowers are native to the Americas and were cultivated by their inhabitants long before the arrival of the Europeans. The seeds of the plants served as a source of food for many Native American tribes, which cracked the shells and ate them whole and pounded them into a flour-like substance used to make bread and cakes.
Native Americans also utilized pigment obtained from the plants as a dye and sunflower oil for cooking and to smooth the hair and skin. When explorers brought the sunflower back to Europe around the early 1500s, the plant became popular as an ornamental and was eventually cultivated in its new home for oil and food production. The sunflower became particularly prevalent in Russia, where growers developed different varieties to serve specific purposes.
Approximately 60 species of sunflowers, which comprise the genus Helianthus, have been identified, but only a small number of them are grown commercially. The plants vary significantly in size, but are generally quite tall and hardy. The tallest specimen on record measured more than 25 feet high. The broad leaves of the sunflower spiral around the plantís hairy stem and the flower head is flat. Two types of florets comprise the head: the disk flower and ray flowers. The disk flower is the central, dark part of the flower, which is composed of numerous, small flowers tightly packed together. The ray flowers are the elongated yellow or orange petals that are arranged around the disk flower.
When sunflowers are in bloom, most of the flower heads face the east as if they want to greet the rising sun each morning. Before they blossom, however, sunflower buds actually track the sunís path across the sky, slowly turning from east to west on bright sunny days before eventually returning to their eastward direction at night or first light the following morning. This remarkable act of heliotropism has been linked to motor cells located in a bendable segment of the sunflower stem located directly beneath the bud. When blooming occurs, this segment loses its flexibility and the flower head assumes a stationary position.
Nathan S. Claxton, Shannon H. Neaves, and Michael W. Davidson - National High Magnetic Field Laboratory, 1800 East Paul Dirac Dr., The Florida State University, Tallahassee, Florida, 32310.