A meristematic tissue consists of a group of cells which remain in a continuous state of division or they retain their power of division. They are composed of immature cells which are in a state of division and growth. Usually the intercellular spaces are not found among these cells. The meristems usually occur at the apices of all main and lateral shoots and roots and thus their number in a single plant becomes quite large. In addition, plants bearing secondary increase in thickness possess extensive meristems, the vascular and cork cambia, responsible for the secondary growth.
This is a tissue formed by a group of cells(mitosis). Meristem cells aren't specialized, but when they divide, some of the new cells specialize into tissues. Areas of growth that lengthen the tips of roots and stems are called apical meristems. Lateral meristems, found all along woody roots and stems, increase the thickness of these plant parts.
i totally agree with mr. elekzy.. basically the apical meristam are persent in young shoot, coz they require rapid growth and have to manage and adopt themselves in the harsh weather.. so they divide mitotically.....as for as lateral meristem are concenred they are presetn on either side of the shoot and stem, another type of meristem is intercalary meristem such as in sugar cane...