Auxin is produced by the apical meristem and is transported to the side of the stem opposite the light stimulus, causing the cells on the "dark" side to elongate more and the stem to grow (bend) towards the light.

Some sketches of how they figured it out at: The discovery of auxins: phototropism

"Auxin is produced by the apical meristem and is transported to the side of the stem opposite the light stimulus, causing the cells on the "dark" side to elongate more and the stem to grow (bend) towards the light."

That sentence does not imply that A. is false, i.e., auxin is NOT also transported to the light side where it is destroyed by the light. What experimental evidence disproves A.? If all sides of the plant are illuminated equally, is there a net reduction of auxin in the plant or is it constant?

Phototropism is cool! I loved learning about that in my Botany course.

Indiana.edu site on Phototropism Part I: Light and auxin has diagrams similar to those linked above with a tiny bit more.

As someone already noted, it is a really fascinating field of interest.

In pine shoots, auxin appears not to be made in the apical meristem, but rather in the developing leaves (needles). Removal of the AM does not inhibit stem elongation; plucking off the young needles does inhibit it.