How Do Trees Grow Taller?
Trees grow by producing new cells in a very limited number of places. These places of cell division are called meristems. Meristems are zones of intense activity where all new cells are formed and where they expand.
Trees grow in height as a result of meristems that are located at their branch tips. These meristems are called apical meristems. Roots also expand through the soil by growing at their tips as a result of apical meristems.
All buds that you see on a tree contain apical meristems. Leaf buds enable trees to grow taller and tree branches to lengthen. In the spring, the leaf buds grow and stretch out into leafy twigs or new branches, unfolding leaves as they lengthen, or as they increase the height of the treetop or the length of the branches.
Just under the outer covering (or bark) of a tree is a layer of growing tissue called cambium. The cambium is made up of living cells that add a new ring of wood to the trunk each year. This is the only way a tree trunk can grow thicker.
Cambium also causes branches and roots to grow thicker. The cambium produces new xylem and phloem each year and as a result the trunk, branches and roots continue to increase in diameter.