Modular Shoot Construction:  Series Segmentation or Modulation.

Primary growth occurs in intervals (sometimes called modules or segments).  Each interval consists of a node, axillary bud and internode.  Mini-segments form within the apical meristem; then push through forming the next interval when fully formed.  This contrasts with animal growth where all segments form at the same time.

A Fun Activity.  Write a short essay on modular construction (using the meristems and nodes) of you or your pet to highlight the differences and better understand plant development.

The apical meristem can alter modules "on the fly" during the development of that module.  A sign of this is an irregularity in the morphology of a leaf or group of leaves.  Also, concerning axillary bud growth, when the bud is formed it is juvenile.  But if time passes before shoot formation, that area of the plant matures; and when growth on the axillary shoot occurs, the base of the new shoot will be mature while the rest will be juvenile.

Next:  "Secondary Growth."