(secondary thickening) The increase in diameter of a plant organ resulting from cell division in a *cambium
. Secondary growth results in the formation of secondary tissues, for example the secondary xylem, secondary phloem, phellem, and phelloderm. *Primary tissues
, on the other hand, are derived from primary meristems. Secondary growth occurs in most dicotyledons and gymnosperms and a few monocotyledons. There are relatively few living representatives of lower vascular plants exhibiting secondary growth but it was common in many extinct species.