The vascular cambium is a thin layer of specialized plant cells responsible for the increase in girth of many plants. This tissue is a type of meristematic tissue, consisting of undifferentiated cells that retain the capacity for continuous division and growth. It does not transport water, minerals, or food, unlike the xylem and phloem, but rather produces the cells that form these transport tissues.
Location in Plants
The vascular cambium is found within the stems and roots of many plants, particularly in woody species like dicots and gymnosperms. It is positioned between the xylem, which transports water, and the phloem, which transports sugars. In woody plants, the vascular cambium forms a continuous cylinder of meristem cells, creating a ring from which new tissues grow. This cylindrical arrangement allows for the plant’s lateral expansion.
Its Primary Function
The core function of the vascular cambium is secondary growth, the process that allows a plant to increase in diameter. Its cells undergo continuous division, producing new cells both towards the inside and outside of the plant body. Specifically, it generates new secondary xylem cells towards the interior, pushing the primary xylem inwards. Simultaneously, it produces new secondary phloem cells towards the exterior, pushing the primary phloem outwards. This ongoing cell division enables woody plants to expand their girth and develop a robust structure.
The Tissues It Produces
The activity of the vascular cambium results in the formation of two distinct secondary tissues: secondary xylem and secondary phloem. Secondary xylem, commonly known as wood, is produced towards the inside of the cambium ring. This tissue is primarily responsible for the long-distance transport of water and dissolved minerals from the roots to the rest of the plant, and its lignified cells also provide structural support. Secondary phloem forms towards the outside, becoming part of the inner bark, and its main role is to transport sugars produced during photosynthesis from the leaves to other parts of the plant. The differing rates of cambial activity throughout the year lead to the formation of distinct annual growth rings in wood, with wider rings indicating periods of more active growth.
Significance for Plants
The vascular cambium is important for the survival and success of woody plants. Its ability to produce secondary xylem and phloem allows plants to increase their diameter, providing structural support. This increased girth enables plants to grow taller, allowing them to compete more effectively for sunlight. As plants mature, the continuous production of new vascular tissues by the cambium ensures efficient long-distance transport of water, minerals, and nutrients throughout the expanding plant body. This ongoing growth also allows for the replacement of older tissues with new ones, contributing to the plant’s longevity and resilience.