Sunflower, Helianthus annuus, brightfield photomicrograph LS showing vascular structure
Sunflowers in the bud stage exhibit heliotropism. At sunrise, the faces of most sunflowers are turned towards the east. Over the course of the day, they follow the sun from east to west, while at night they return to an eastward orientation. This motion is performed by motor cells in the pulvinus, a flexible segment of the stem just below the bud. As the bud stage ends, the stem stiffens and the blooming stage is reached. Sunflowers in their blooming stage lose their heliotropic capacity. The stem becomes "frozen", typically in an eastward orientation. The stem and leaves lose their green colour. The wild sunflower typically does not turn toward the sun; its flowering heads may face many directions when mature. However, the leaves typically exhibit some heliotropism.
Size: 3413px × 5120px
Photo credit: © Scenics & Science / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: annuus, botany, brightfield, bundles, cutflowers, helianthus, ls, osmosis, phloem, photomicrograph, photosynthesis, showing, structure, sunflower, vascular, xylem
