X-ray examination of the 46 tooth in a 7-year-old child reveals the following: the root walls are parallel, their thickness gradually decreases, they have pointed ends. The root canal converges towards the tooth cavity, and diverges at the developing apical hole. Periodontal gap is of the same width along the enti- re length of the root. At the root apex it merges with the growth zone. Specify the stage of root development: