The key difference between primary and secondary growth is that primary growth is responsible for the vertical growth of plants, primarily occurring in the apical meristems at the tips of shoots and roots. While secondary growth is responsible for the radial growth (increase in girth or diameter) of stems and roots in mature woody plants. It occurs in the cambium layer, which contains lateral meristems (vascular cambium and cork cambium).
What is Primary Growth?
Primary growth refers to the increase in length or height of a plant or its parts, primarily through the activity of the apical meristem. It is responsible for the overall elongation of the plant body, including stems and roots, during the initial stages of plant development. Primary growth occurs in the apical meristems located at the tips of the shoots and roots.
In the shoot system, primary growth leads to the elongation of the stem and the development of new leaves and branches. The apical meristem at the shoot tip produces new cells that differentiate into various tissues, such as the epidermis, cortex, and vascular tissues, contributing to the overall growth of the plant.
What is Secondary Growth?
Secondary growth, also known as lateral or non-primary growth, refers to the increase in girth or thickness of stems and roots in plants. It occurs in woody plants such as trees and shrubs and is responsible for the expansion of their stems and roots, allowing them to grow wider and stronger over time.
Unlike primary growth, which is responsible for the elongation of plant parts, secondary growth occurs in mature plant tissues and is initiated by a specialized lateral meristem called the vascular cambium. The vascular cambium is a thin layer of actively dividing cells that resides between the xylem (wood) and phloem (inner bark) in stems and roots.
Primary vs Secondary Growth
The major difference between primary and secondary growth is given below:
| Primary Growth | Secondary Growth | |
| Definition | Increase in length of stems and roots. | Increase in girth (diameter) of stems and roots |
| Occurs in | Herbaceous plants and young woody plants. | Mature woody plants |
| Types of tissues | Primary xylem and phloem. | Secondary xylem and phloem. |
| Growth pattern | Continuous. | Intermittent. |
| Significance | Establishes basic plant shape. | Increases structural strength and support. |
| Aspect | Primary Growth. | Secondary Growth. |
| Location | Occurs at apical meristems (tips of roots and shoots). | Occurs at lateral meristems (cylindrical meristems). |
| Responsible Meristem | Apical Meristems. | Lateral Meristems (vascular cambium and cork cambium). |
| Plant Structures | Contributes to the lengthening of roots and shoots. | Contributes to the thickening of stems and roots. |
| Tissues Involved | Involves primary meristems (protoderm, ground meristem, procambium). | Involves secondary meristems (vascular cambium and cork cambium). |
| Cell Division Type | Usually involves cell division through mitosis. | Involves both cell division through mitosis and cell enlargement. |
| Result | Increases plant height and primary plant body. | Increases plant girth and secondary plant body. |
| Dominance | Occurs throughout the plant’s life. | Mostly occurs in woody plants at later stages. |