Does a Plant Grow Toward the Light?

by Lynn Moran

Overview

The plant in your window looks like it's growing toward the light. You turn it around and go to work. When you come home, it's leaning toward the light again. You have to wonder, do plants grow toward the light? Yes, they do.
Phototropism

It's called phototropism and when it occurs, the plant is actually growing toward the light, not simply bending or reaching in that direction.

History

Augustin Pyrame de Candolle theorized, in 1809, that plants were actually growing toward the sun. Charles Darwin followed several decades later with some experiments that suggested this response had to do with the tops of the seedlings because when he covered that part of the plant, phototropism didn't occur.
Auxin

Eventually, scientists discovered auxin, a type of hormone, produced in plants.
Effects

Auxin is produced, as Darwin's experiments suggested, in the new tips of the plants and then distributes itself throughout the plant. When one side of the plant receives less light than another, more auxin goes to the darker side, causing it to grow faster and lean toward the light.
Fun Fact

Not only does auxin cause the shoots of the plants to grow upward, it also causes the roots to grow down. This is known as "gravitropism."