A thin strip of primary meristem is found in dicotyledonus stem between xylem and pholem is called cambium. The cells of cambium are thin-walled rectangular. The cambium strip may be uniseriate or biseriate and multi-layered. The cambial cells are living elongated having with oblique ends. They look rectangular in cross section as they are flattened tangentially.

Types of Cambium:

Cork cambium (pl. cambia or cambiums) is a tissue found in many vascular plants as part of the epidermis. The cork cambium is a lateral meristem and is responsible for secondary growth that replaces the epidermis in roots and stems. It is found in woody and many herbaceous dicots, gymonosperms and some monocots (monocots usually lack secondary growth). It is one of the plant's meristems – the series of tissues consisting of embryonic disk (incompletely differentiated) cells from which the plant grows. It is one of the many layers of bark, between the cork and primary phloem

The unifacial cambium (pl. cambia or cambiums) produces cells to the interior of its cylinder. These cells differentiate into xylem tissue. Unlike the more common bifacial cambium found in later woody plants the unifacial cambium does not produce pholem to its exterior. Also in contrast to the bifacial cambium, the unifacial cambium is unable to expand its circumference with anticlinal cell division. Cell elongation provides a limited amount of expansion.

The vascular cambium is the main growth layer in the stems and roots of many plants, specifically in icots such as buttercups and oak trees, and gymnosperms  such as pine trees. It produces xylem on the inside and phloem on the outside. In herbaceous plants, it occurs in the vascular bundles which are often arranged like beads on a necklace forming an interrupted ring inside the stem. In woody plants, it forms a continuous ring and grows new wood on the inside.

https://en.wikipedia.org/wiki/Cambium