A is the meristem contributes for increase in length of a stem and B is the meristem that contributes for increase in girth of the stem. A and B are respectively

Apical meristems and intercalary meristems are types of primary meristems that contribute for increase in length or primary growth of plant axis. The lateral meristems like Cork cambium and Vascular cambium (fascicular and interfascicular cambia) are involved in increase in girth of the axis by forming secondary permanent tissues towards the periphery and towards the center.