Plant roots always grow downward because specialized cells in root caps detect and respond to gravity. This is an example of a tropism. A tropism is a turning toward or away from a stimulus in the environment. Growing toward gravity is called geotropism . Plants also exhibit phototropism , or growing toward a light source. This response is controlled by a plant growth hormone called auxin . As shown in Figure below , auxin stimulates cells on the dark side of a plant to grow longer. This causes the plant to bend toward the light.
Sue loved having  pretty plants in her apartment but often forgot to take care of them. One day she was sitting in the kitchen and noticed her aloe was was growing  with all the branches curving towards the window. When she picked it up to turn it she notices some of the roots were growing out of the bottom of the pot. She sighed and made a mental note to stop at the garden center for a deeper pot tomorrow.
Where the branches growing towards or away from the sunlight?