Theoretically, growth and dierentiation in higher plants are open. This means that there is no limit to the ‘extent a plant part can grow. But it is more correct to say that development and differentiation is open in higher plants. Once a cell loses its capacity to divide then it differentiates.
Differentiation is the process by which a particular plant starts doing the job it is meant to do.
For example, the job of a leaf is to make food for plant. Sometimes environment or a particular phase of growth can dictate a particular part to behave differently. This is the phase when re-differentiation occurs and the plant part takes on a new role. Thus, it can be said that development and differentiation are open to change under the given environmental conditions and demands of those conditions.