The main growing points in plants are the shoot and root meristems.
A flowering plant's apical meristem or shoot tip is described by the tunica-corpus theory of meristem organization, where cell layers or tunica cover the body or corpus of the stem.
Photomicrograph of a shoot tip showing the apical meristem between two developing leaves.
Satina and Blakeslee (1941) described the tunica of the dicot shoot meristem as having distinct layers.
They called the tunica layers
L-I, L-II, and L-III.
Gymnosperm meristems do not have layers, but have zones.
A few apical initials are responsible for new stems and leaves.
The root meristem lies under a protective root cap.