| In shrubs and trees the vascular cambium remains active for the life of the plant. Each year it produces new phloem on the outside (in the bark) and xylem on the inside. As the xylem builds up it forms the woody trunk of the tree. The rings in a tree trunk mark the beginning of active growth growth each spring and the end of growth in the fall. The growth of the inside of the stem breaks the original skin of the stem. Another cambium develops under the skin and produces cork cells that form the outer layers of bark. |
Woody stem structure
