Auxin and gravitopism

Geotropisms

Gravitropism (also called geotropism) is a response of plant roots to the stimulus of . They grow downwards as a result of gravity.

Plants responses to gravity:

when the stem grows against the force of gravity, this is known as a negative geotropism
when a root grows in the direction of the force of gravity, this is known as a positive geotropism

Just like phototropism, geotropism is also caused by an unequal distribution of auxin.

In a root placed horizontally, the bottom side contains more auxin and grows less - causing the root to grow in the direction of the force of gravity.

The opposite happens in a stem. When a stem is placed horizontally, the bottom side contains more auxin and grows more - causing the stem to grow upwards against the force of gravity.