Cambium is a layer of material inside a plant or tree which consists of actively dividing cells which generate growth for the plant. The cambium is filled with undifferentiated cells which have the ability to differentiate into many different types of cells, depending on where in the plant they are growing. This part of a plant can be vulnerable to damage; if a plant is cut through the cambium or serious injuries occur, the plant may die.
There are actually two kinds of cambia. The vascular cambium is found inside the tissues of the plant, between the xylem and the phloem. It is responsible for the width and outward growth seen as plants mature and grow larger. In trees, it develops in distinct seasonal rings as the amount of nutrients rises and falls, and can be used as a method of dating the age of the tree, in addition to tracking weather patterns. A thin ring indicates that a tree struggled for water and nutrients, while a thick ring illustrates ample supplies of food and water.
Some vascular plants also have what is known as a bark or cork cambium. This structure is on the outside of the plant, forming a rough outer layer which protects the plant from damage. In the case of the cork tree, the cork is commercially useful, as it can be harvested and used for a variety of purposes. The cork cambium is less vulnerable to damage than the vascular cambium, because it is designed as a form of armor for the plant, and must be able to withstand rough treatment.
This area of a plant's anatomy is of special interest because it can provide so much information about growing conditions for the plant. When conditions are good, the cells in the cambium are stimulated to divide and reproduce rapidly, producing a thick layer. When conditions are poor, the cells may struggle to divide, and the cambium can be thin and irregular. Studying this region of a shrub or tree's internal structures can be one way to learn about growing conditions.
Awareness of this area of plant anatomy is also important for gardeners. They need to create growing conditions which will encourage the steady growth of this area of the plant, and they also need to consider the cambium when they are establishing grafts. Grafting requires careful alignment of the scion and stock being grafted so that their tissues will align. If the various parts of the branch are not aligned, the scion will die from lack of nutrients, or the growth will be irregular.