What Is Primary Growth?
All plant growth occurs by cell division elongation. Cell division occurs primarily in regions of undifferentiated cells known as meristems. Cell division in the apical meristems and subsequent elongation and maturation of the new cell produces primary growth.
Therefore, primary growth can be defined as is growth that occurs as a result of cell division at the tips of stem and roots, causing them to elongate and give rise to primary tissue. The growth of shoots and roots during primary growth enables plants to continuously seek water (roots) or sunlight (shoots).
The plant body grows lengthwise chiefly by the enlargement of cells produced by the apical meristem (rather than by cell division). Because they lack secondary tissues, most monocots and herbaceous plants grow solely by primary growth until they reach maturity, when growth stops.
What You need to know About Primary Growth
- Primary growth can be described as the increase in length of the shoot and root. It is as a result of cell division in the shoot apical meristem.
- The primary growth of the plant occurs at the beginning.
- Occurs by the action of the apical meristem.
- Primary growth occurs primarily at the apical (top) bud, rather than auxiliary buds (buds at locations of side branching).
- Primary growth occurs in all parts of all plants.
- The epidermis, cortex and the primary vascular tissues are developed during the primary growth. Primary tissues include: primary xylem and primary phloem.
- The primary growth results in the growth in the longitudinal axis.
- Primary growth stops after completion of the tissue differentiation.
What Is Secondary Growth?
Secondary growth is the growth that results from cell division in the cambia or lateral meristems and that causes the stems and roots to thicken. Secondary growth occurs in gymnosperms, most eudicots and woody magnoliids (such as the magnolia). Most monocots and herbaceous plants undergo little or no secondary growth but simply stop growing when their primary tissue matures.
In many vascular plants, secondary growth is the result of the activity of the two lateral meristems, the cork cambium and vascular cambium. Arising from lateral meristems, secondary growth increases the girth of the plant root or stem 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 shapes the plant into a tree with a thickened trunk.
The formation of secondary vascular tissues from the cambium is a characteristic feature of dicotyledons and gymnosperms. The function of cork cambium is to produce the cork, a tough protective material. 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. In the living pteridophtes this feature is rare but occurs in plants like Isoetes and Botrychium.
What You Need To Know About Secondary Growth
- Secondary growth is the increase in thickness or girth of plant.
- Secondary growth follows the primary growth.
- The process of secondary growth is controlled by the lateral meristems and is similar in both stems and roots.
- Secondary growth occurs only in (dicots) angiosperms and gymnosperms. Secondary growth does not occur in monocots, due to absence of cambium in monocots.
- The combined actions of the vascular and cork cambium result in secondary growth/widening of the plant stem.
- The bark, periderm, lenticels, secondary phloem and secondary xylem develop during secondary growth.
- The secondary growth results in the radial growth.
- The secondary growth only occurs in the mature parts (parts that are completely developed).
Similarities Between Primary And Secondary Growth
- Primary and secondary growth take part in increasing the size of the plant
- Both primary growth and secondary growth occur in woody plants.
- Meristematic tissue is involved in both primary and secondary growth of the plant.
Also Read: Difference Between Phloem And Xylem
Difference Primary And Secondary Growth In Tabular Form
|BASIS OF COMPARISON||PRIMARY GROWTH||SECONDARY GROWTH|
|Effect||Primary growth increases the length of the shoot and root.||Secondary growth is the increase in thickness or girth of plant.|
|Occurrence||The primary growth of the plant occurs at the beginning.||Secondary growth follows the primary growth.|
|Growth Process||Occurs by the action of the apical meristem.||The process of secondary growth is controlled by the lateral meristems and is similar in both stems and roots.|
|Occurrence||Primary growth occurs primarily at the apical (top) bud, rather than auxiliary buds (buds at locations of side branching).||Secondary growth occurs only in (dicots) angiosperms and gymnosperms. Secondary growth does not occur in monocots, due to absence of cambium in monocots.|
|Growth Areas||Primary growth occurs in all parts of all plants.||The combined actions of the vascular and cork cambium result in secondary growth/widening of the plant stem.|
|Tissues||The epidermis, cortex and the primary vascular tissues are developed during the primary growth. Primary tissues include: primary xylem and primary phloem.||The bark, periderm, lenticels, secondary phloem and secondary xylem develop during secondary growth.|
|Type Of Growth||The primary growth results in the growth in the longitudinal axis.||The secondary growth results in the radial growth.|
|Growth Period||Primary growth stops after completion of the tissue differentiation.||The secondary growth only occurs in the mature parts (parts that are completely developed).|
Importance Of Secondary Growth
- It increases the width and thickness of plants.
- Provides support to the increasing weight of the aerial growth.
- It increases the girth of plant; this eventually increases the amount of water and nutrients to support the growing number of leaves.
- It provides a corky bark around the tree trunk that protects the interior parts from abrasion, heat, cold and infection.
- It adds new conducting tissues for replacing old non-functioning ones as well as for meeting increased demand for long distance transport of sap and organic nutrients.