Lateral Meristem - Secondary Growth
Small plants (green stems) only primary growth
Trees, shrubs (wood) have secondary growth by lateral meristem (peripheral cylinders of meristem tissue)
Bark: cork cambium ? cork cells of outer bark
Beneath bark: vascular cambium ? secondary xylem & phloem; secondary xylem = wood
Year rings: secondary xylemcold in winter ? slow growth ? small xylemwarm in summer ? fast growth ? large xylem
No year rings in tropical wood