Plant cuttings naturally want to continue producing new stems and foliage. Successful rooting involves encouraging cuttings to stop producing stem cells and start producing root cells. The proper use of rooting hormone can speed this process up considerably.
How Hormones Work
When rooting hormones are applied to the end of a plant cutting, its stem cells are replaced with undifferentiated cells that eventually turn into root cells. The new cells form calluses at the site of the cut, and the hormones hasten the appearance of root cells that will produce strong healthy roots.