The time interval between the formative phase and the maturation phase of plant growth is known as
Grand period of growth
The formative phase is also called the phase of cell division. New cells are produced by mitotic divisions having meristematic tissue.
Phase of maturation or differentiation is the development of special types of cells by undergoing structural and physiological differentiation.
The intermediate phase between the formative phase and the maturation phase is the phase of elongation.