|apical meristem |
A meristem at the tip of a plant shoot or root that produces auxin and causes the shoot or root to increase in length. Growth that originates in the apical meristem is called primary growth. In vascular plants, the apical meristem produces three kinds of primary meristems: the protoderm, ground meristem, and procambium. These in turn produce primary tissues. See more at meristem.