The answer is auxin can move to the shady side of the stem.
Phototropism is a reaction to environmental factors. It is a plant's response to sunlight in the form of movement. In plants, phototropism is very prevalent. In actuality, it is necessary for plant growth. Other plant movements also occur in response to touch, water, gravity, and other factors. Phototropism was discovered due to well-known experiments by Charles Darwin and Boysen Jensen.
