auxin

[gidthekid]

How do auxins affect gravitropism?

[sabrinah]

Auxin, which is a plant hormone responsible for cell elongation, makes a plant respond accordingly to gravitropism, (basically gravitational forces) both positively, when roots grow downward, and negatively, when shoots grow up. If you place a seed in the soil horizontally, within hours the seedling realigns itself so that the roots grows down and the shoots row up. Charles Darwin spotted this effect in the late 19th century.