Vascular cambium occurs in the stele. The cells of cambium remain surrounding the primary xylem in both stems and roots. The vascular cambium is one cell thick permanent secondary meristem.
It is often described as cylindrical and develops between primary xylem and-phloem. It is present in stems and roots and in their branches. It extends from tips to the bases of stems and roots. It may even extend into leaf petioles in some woody plants.
In the stele of stem, the cylinder of cambium consists of fascicular- and interfascicular cambium. In a vascular bundle of dicotyledonous stem the fascicular cambium occurs between primary xylem and —phloem. The interfascicular cambium originates from the parenchyma tissue that occurs between the two vascular bundles.
Fascicular and interfascicular cambium together compose a cylinder of cambial cells. The cylinder of cambial cells, once complete, divides chiefly by periclinal division. The inner derivatives differentiate into a cylinder of secondary xylem and the peripheral derivative cells form a cylinder of secondary phloem.
Cambial initials have primary walls. The walls are thin, non-lignified and have primary pit fields only. Plasmodesmata pass through the pit fields. Plasmodesmata connect the protoplast of adjacent cambial cells or cambial derivative cells. It is regarded that the symplastic connections or plasmodesmata are the path of hormone transmission to the sites of developing xylem and phloem cells.
The submicroscopic structure of the cells of cambium, in general, resembles those of other meristematic cells. Each cell contains nucleus, ribosomes and dictyosomes, Golgi bodies, endoplasmic reticulum, mitochondria, spherosomes etc. Variations in cell organelles are observed and this can be seasonal or taxonomic.
As for example in the early phases of dormancy some species have plastids with abundant starch grains while species of other taxa lack them. Cyclosis, i.e. streaming of cytoplasm occurring during cytokinesis, is more conspicuous in fusiform initials than ray cell initials. In arborescent species, the plastids of cambial cells do not form grana although grana are formed in the plastids of herbaceous species.
In Fagus sylvatica, the cells of resting cambium contain lipid droplets and protein bodies. Electron microscopic study reveals that unlike most other meristematic cells, the cells of vascular cambium are highly vacuolated. It is thought that vacuoles may be formed by the dissolution of stored lipids and proteins when the cambium resumes its activity after resting period.