Model of a Primary Thickening Meristem
| The Green rectangles represent Leaf Primordia. The red curve represents the PTM. The white rectangles represent Nodes along the flank of the stem.
Remember that the leaves define nodes. Thus, each green leaf defines a node. Leaves on the side of the stem are not shown but one leaf defines each node that is shown. In some plants this meristematic activity continues on the flank of the apex and extends downwardly in the stem where it is called the "Secondary Thickening Meristem" (STM).
The activity of this meristem leads to an increase in stem diameter. Most of the cells in the STM divide periclinally and produce derivatives principally towards the center of the stem. This is reminiscent of the Vascular Cambium in dicots. However, it has some fundamental differences as we will see. |
