Cambium

Cambium

The cambium is a layer of actively dividing cells responsible for the secondary growth of stems and roots in plants. It is found between the xylem and phloem in dicotyledonous and gymnosperm plants. The cambium is essential for increasing the girth (diameter) of a plant, contributing to its overall strength and stability.

The cambium itself is not a solid layer, but rather a thin zone composed of two main types of cells:

• Fusiform initials: These elongated cells are oriented vertically and give rise to the secondary xylem (wood) towards the inside of the stem or root and the secondary phloem (inner bark) towards the outside. They also contribute to the axial system of the plant.
• Ray initials: These cells are more isodiametric (roughly equal in all dimensions) and produce the radial system of the plant, including vascular rays that transport water and nutrients laterally across the stem or root.

The division of cambium cells is influenced by various environmental and hormonal factors. During periods of active growth, the cambium divides rapidly, producing new xylem and phloem cells. The xylem cells become lignified, forming the hard wood of the plant, while the phloem cells transport sugars and other organic compounds throughout the plant. In temperate climates, cambial activity often slows or ceases during the dormant season.

The age of a tree can be estimated by counting the annual rings visible in the secondary xylem, which represent the growth increments of each year. Variations in ring width can provide information about past environmental conditions, such as rainfall and temperature. Damage to the cambium can have serious consequences for a plant, as it can disrupt its ability to transport water and nutrients and can lead to weakening or death.