What causes a green plant exposed to the light on only one side, to bend toward the source of light as it grows 

What causes a green plant exposed to the light , on only one side , to bend towards the source of light as it grows ?

What case a green plant exposed to the light on only one side to bend towardsthe sourceof light as it growns?

What causes a green plant to bend towards light as it grows ?

What causes a green plant to bend towards light as it grows ?

What causes a green plant to bend towards light as it grows ?

A decapitated plant exposed to unilateral light

A decapitated plant exposed to unilateral light