1. Charles Darwin and his son Francis Darwin performed some experiments on phototropism.
2. They covered the terminal portion of the tip of stem (coleoptile) with a cylinder of metal foil.
3. Exposed the plant to light coming from the side.
4. The characteristic bending of the seedling did not occur.
5. If light was permitted to penetrate the cylinder, bending occurred normally.
6. They concluded that when seedlings are freely exposed to a lateral light some influence is transmitted from upper to the lower part causing the material to bend.
