Secondary growth

The formation of secondary vascular tissues from the cambium is a characteristic feature of dicotyledons and gymnosperms.

In certain monocots, the vascular tissues are also increased after the primary growth is completed but the cambium of these plants is of a different nature.

Arising from lateral meristems, secondary growth increases the width of the plant root or stem, rather than its length.

[2] Abnormal secondary growth does not follow the pattern of a single vascular cambium producing xylem to the inside and phloem to the outside as in ancestral lignophytes.

Some dicots have anomalous secondary growth, e.g. in Bougainvillea a series of cambia arise outside the oldest phloem.

Secondary growth thickens the stem and roots , typically making them woody . Obstructions such as this metal post and stubs of limbs can be engulfed.
Diagram of secondary growth in a tree showing idealised vertical and horizontal sections. New wood is added in each growth season by the lateral meristems, the cork cambium and vascular cambium .
Palms (in the picture Roystonea regia palm) increase their trunk diameter by means of division and enlargement of parenchyma tissue, without a real secondary growth (production of secondary vascular strands—secondary xylem and phloem tissues—with the consequent enlargement of the canopy and root system). [ 3 ]