Secondary Growth in Roots: Secondary growth is an increase in diameter/girth/circumference due to the addition of secondary tissue(secondary cortex, secondary phloem, and secondary xylem) formed by the activity of vascular cambium in stelar region(region inside pericycle) and cork cambium (phellogen) in extrastelar region (the region outside pericycle i.e., cortex). It is found in the dicot stem, dicot roots, and gymnosperms. Herbs, shrubs, and hydrophytes do not show secondary growth. Monocots rarely show secondary growth(e.g., Aloe, Dracaena, Agave).

Secondary growth also occurs in stems and roots of gymnosperms. However, secondary growth does not occur in monocotyledons.

Different stages of Secondary Growth in Roots

• Vascular rays: In secondary growth first of all, these rays start emerging from the radially arranged cells and they are involved in giving height to the roots. These rays are present in the xylem tissues. They may be made up of one type of cells or may have different types of the cells.
• Secondary phloem: This is the covering layer outside the vascular cambium. It is made up of the same cells which are found in primary phloem tissue. It is a regular arrangement of the tissues and has no fibre in it.
• Secondary xylem: This is the woody part of the roots and made up of the vessels, fibres, parenchyma tissues and tracheids.

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By Team Learning Mantras