Primary Growth: Cells of apical meristems divide, differentiate and develop to form primary tissues. As a result, the plant grows in length. This is called primary growth.- Secondary Growth: By the activity of secondary lateral meristems, increase in the circumference/girth of the plant organs due to the formation of secondary tissues in stelar & extra stelar regions, is called as secondary growth.- Normally secondary growth takes place in roots and stem of dicotyledons & gymnosperms.- Due to lack of cambium in monocotyledons, secondary growth is absent. But exceptionally secondary, growth takes place in some monocotyledons. Such as - Palm, Yucca, Dracaena, Smilax, Agave, Coconut etc.