Nelson,
Inside a branch are two types of cells: shoot apical meristem and adventitious meristem. The shoot meristem is responsible for the growth at the branch's tip. The adventitious meristem are quieter cells and lie in the branch waiting to do something. These are the cells that become new branches when the growing tip is damaged or removed (see Herman's pinching technique to increase branching.) When rooting a cutting, these adventitious cells are convereted to root apical meristem. This takes time and, by the collective observation of the forum members, varies by variety, location, medium, etc.
FWIW: I am rooting 'Black Madeira' for the second time. After a month in sphagnum moss, they did not form initials. I went ahead and potted them up, after being potted up for 20 days, they still don't feel as if they've rooted. They are my hardest rooter this year, followed by '278-128' and 'Peter's Honey'.
~james