What is Primary Growth in Shoot?

The growth in height of a plant stem results from the division of cells at the apex, or tip of the stem, called the shoot tip. Here, a group of cells form a raised dome called an apical meristem, which is located at the very tip of a shoot, a part of the bud. This meristematic tissue is very similar to what is found in the root tip, except that this apical meristem is formed from a terminal bud found at the tip of the stem. So a "bud" consists of a rounded dome of dividing cells that are enclosed and protected by scales, until they start to grow new cells. Similar to the root, the shoot apical meristem also gives rise to three primary tissues known as: the protoderm, the ground meristem, and the procambium.

Other structures in the shoot tip that deserve attention are the leaf primordia. These are tiny embryonic leaves that develop along with the shoot tip. The leaf primordia are located around the apical meristem dome, and their points of origin (called nodes) determine the ultimate pattern of leaf arrangement - in other words, are they alternately, or oppositely arranged around the twig?

As new cells are added by the apical meristem, the shoot elongates and increases in height. There are regions of elongation and maturation that are similar to those in the root tip, but additionally, the ground tissue will also form tissues known as the pith and cortex.