How do rooting compounds work?
Answers:
They contain a plant hormone called Gibberellic acid.
From Wikipedia:
Gibberellic acid is a hormone found in plants. Gibberelic acid is a simple gibberellin promoting growth and elongation of cells. Affects decomposition of plants. Helps plants grow if used in small amounts, but eventually plants grow a tolerance for it. Gibberellic acid stimulates the cells of germinating seeds to produce mRNA molecules that code for hydrolytic enzymes.
It was first discovered in Japan in 1935 as a result of the study of a condition common in rice plants called "foolish seedling" disease, which caused the plants to grow much taller than normal. The effects of gibberellins weren't widely understood until years later.
Gibberellic acid is a very potent hormone whose natural occurrence in plants controls their development. Since GA regulates growth, applications of very low concentrations can have a profound effect while too much will have the opposite effect.
Gibberellic acid is sometimes used in laboratory and greenhouse settings to trigger germination in seeds that would otherwise remain dormant.