Nuclear Invagination and Nuclear Vacuole Formation in Several Plants ORGANELLE INVAGINATION AND FORMATION/DEGRADATION OF NUCLEAR VACUOLE Plasmalemma Invaginations in Cultured Callus of Stevia rebaudiana: Ultrastructure and Ultracytochemical Localization of Acid Phosphatase TONOPLAST INVAGINATIONS AND INTRAVACUOLAR VESICLES IN CULTURED CALLUS CELLS OF STEVIA REBAUDIANA