How does a rigid plant bend or grow to one side? Plant cells contain a substance called aurins. This substance has a tendency to move away from the light. Aurins make the cells on the darker side grow faster than the cells on the lighted side.
This causes the stems and the leaves to bend or lean towards the lighted side. The concentration of aurins on the dark side may be due to the fact that sunlight slows or kills these aurins when light falls on them. However, as long as one part of the plant gets sunlight, it can make food and the whole plant survives.