Trunk diameter growth occurs as a result of another meristem already mentioned called the vascular cambium. The vascular cambium produces new xylem and phloem each year and as a result the trunk, branches and roots continue to increase in diameter. Have you ever seen a fence wire or board grown into a tree?
That is the result of the vascular cambium. Cells that are produced in the spring are larger with thinner cell walls. All woody trees have an outer bark that constantly renews itself and protects the tree from pest attacks and environmental impacts such as fire and mechanical injury. Some trees have thick bark that is resistant to injury.
Others are easily injured because they have thin bark. As the tree grows in thickness, the outer part has to give, forming ridges and cracks in the bark. Eventually the outer bark sloughs off. Roots can grow in length diameter, and number. At the tip of a root is the root cap. This cap protects the root and must be constantly replaced as a root pushes through the soil.
Behind the root cap is a meristem which produces new cells for the root cap and for root elongation. These new cells elongate, divide and differentiate into root parts as it pushes through the soil. Root diameter growth is similar to growth in the stem with the vascular cambium producing wood xylem and bark phloem.
A couple differences between root and shoot diameter growth are: 1 cambial growth is much more irregular in roots resulting in roots that are oval or irregular in cross section, and 2 there is greater variation in diameter with age and with horizontal roots compared to vertical roots.
Roots can also grow new lateral roots that form and branch off the main root. Some cells located in a layer inside the root produce a new root primordium.
This new meristem divides and elongates pushing the root out through the parent root. During the process of transpiration, water evaporates from the foliage through openings in leaves called stomata pulling adjoining water molecules with it. This pulling action helps draw water and nutrients up the trunk and into the leaves. In addition, some trees may be capable of exerting a pumping action to push water up the tree.
Photosynthesis, carried out in foliage, twigs and other green plant parts, produces sugars and other components that are used by the tree to carry out its many functions. Sugars, growth regulators, and proteins are moved about the plant in the phloem. Want to help trees and nature? Plant a tree today! As the need for reforestation is global and ever-changing, we feature where trees are most needed now.
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