Secondary Xylem-Wood-1

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The Vascular Cambium is the source of Secondary Xylem in Dicots. Some Monocots have a Lateral Meristem called the Secondary Thickening Meristem which produces Secondary vascular tissues. We will deal with the Secondary Thickening Meristem later.

This model tries to depict the cycle of cell growth and division which occurs in the Vascular Cambium. "Initials" enlarge and divide periclinally. Some derivatives are displaced towards the inside and become Secondary Xylem. Others are displaced to the outside and become Secondary Phloem.

Preiclinal divisions in the Vascular Cambium produce radial rows of cells. Those displaced to the inside become Secondary Xylem. Because the walls of xylem cells are generally thick and lignified, they resist compression and decay. Secondary xylem that accumulates substantially over time is called Wood.