Vascular Cambium - Origin

Origin

Vascular cambium arises from the primary meristem, procambium that remains undifferentiated between the primary xylem and primary phloem. Upon maturity, this region known as the fascicular cambium, and the area of cells between the vascular bundles (fascicles) called pith rays becomes what is called the interfascicular cambium. The fascicular and interfascicular cambiums, therefore, represent a continuous ring which bisects the primary xylem and primary phloem. The vascular cambium then produces secondary xylem on the inside of the ring, and secondary phloem on the outside, pushing the primary xylem and phloem apart.

The vascular cambium usually consists of two types of cells:

• Fusiform initials (tall cells, axially oriented);
• Ray initials (almost isodiametric cells - smaller and round to angular in shape).

The vascular cambium is a type of meristem - tissue consisting of embryonic (incompletely differentiated) cells from which other (more differentiated) plant tissues originate. Primary meristems are the apical meristems on root tips and shoot tips. Another lateral meristem is the cork cambium, which produces cork, part of the bark. Together, the secondary vascular tissues (produced by the vascular cambium) and periderm (formed by the cork cambium) makes up the secondary plant body.

Vascular cambia are found in dicots and gymnosperms but not monocots, which usually lack secondary growth. For successful grafting, the vascular cambia of the stock and scion must be aligned so they can grow together. In wood, the vascular cambium is the obvious line separating the bark and wood.