Meristematic tissue only can divide in a plant body.Wehn they divide ,they form new cells.The new cells formed will specialise to form permanenet tissue. So meristematic tissue will be there adn permanenet tissue will slo be there.
Meristematic tissue will be as it is but when it divides ,the new cells formed will become permanent tissue.So meristematic tissue will also be there in a mature plant and also prermanent tissue.
Plant grows through out its life and growth in plant is due to meristematic tissue only.
So you will find both in the mature tissue.