In botany , secondary growth is growth that results from cell division in cambia or lateral meristems and that causes stems and roots to thicken, while primary growth is growth that results from cell division at the tip of stems and roots. occurs as a result, causing them to elongate, and give rise to primary tissue. Most seed plants have secondary growth, but monocots usually lack secondary growth. If they have secondary growth, it differs from the typical pattern of other seed plants.
The formation of secondary vascular tissues from cambium is a feature of dicotyledon and gymnosperms . In some monocots, vascular tissue also increases after the completion of primary growth but the cambium of these plants is of a different nature. This feature is rare in living pteridophytes, but occurs in plants such as Isoetes and Botrychium .
Lateral separator
In many vascular plants , secondary growth is the result of the activity of two lateral meristems, the cork cambium and the vascular cambium . Originating from the lateral meristem, sec. growth increases the width of the root or stem of the plant rather than its length. As long as the lateral meristems continue to produce new cells, the stem or root will continue to grow in diameter. In woody plants , this process produces wood , and in a plant-shaped tree with a thickened trunk.
Since this growth usually breaks the epidermis of the stem or roots, plants with sec. growth usually also develop cork cambium . The cork cambium gives rise to thickened cork cells to protect the plant surface and reduce water loss . If it is kept for several years, this process can produce a layer of cork. In case of cork oak it will produce harvestable cork .
In nonwoody plants
Secondary growth is also found in many nonwoody plants, such as tomatoes , [1] potato tubers , carrot main root and sweet potato tuberous root . Some long-lived leaves also have secondary growth.
Abnormal secondary growth
Abnormal sec. growth does not follow the pattern of a single vascular cambium that produces xylem from the inside and phloem to the outside as in ancestral lignophytes. Some dicots have asymmetrical sec. growth, such as Bougainvillea , a series of cambia arising out of the oldest phloem. [4]
Ancestral monocots lost their secondary growth and their steel has changed in such a way that it cannot be recovered without major changes which are unlikely to occur. Monocots either have no sec. growth, as is the case with the ancestral, or they have some sort of “asymmetrical sec. growth”, or, in the case of palms, they may or may not have their diameter as a type of sec. growth. Based on the definition given to the word. Palm trees increase their trunk diameter due to division and growth of parenchyma cells, referred to as “primary gigantism” [3] because there is no production of secondary xylem and phloem tissues, [3] [5] or Sometimes called “diffuse secondary growth”. And with heterogeneous sec. growth in dracaena , a cambium is formed, but it produces vascular bundles and parenchyma internally and parenchyma externally. The increase in diameter of some monocotyle activity of a primary concentric meristem derived from the apical meristem.
