Spot X-ray is performed for a 12-yearold child. The X-ray film shows the 35 tooth root to be of nornal length, its walls are parallel to each other and gradually thin out towards the apex. At the entrance the root canal is slightly smaller in diameter than near the forming apex. The periodontal fissure is uniformly wide along the whole length of the formed part of the root. In the apical area of the root it merges with growth zone. What stages of root and periodontium development correspond with this X-ray image?