Primary growth is controlled by root apical meristems or shoot apical meristems, while secondary growth is controlled by the two lateral meristems, called the vascular cambium and the cork cambium. Not all plants exhibit secondary growth.

The key difference between primary and secondary growth is that primary growth increases the length of roots and shoots as a result of cell division in the primary meristem while secondary growth increases the thickness or the girth of the plant as a result of cell division in the secondary meristem.

Answer: The primary root grows vertically downwards into the soil. Smaller lateral roots known as the secondary roots are produced on the primary root. These roots grow in various directions and help in fixing the plant firmly into the soil.

Primary growth allows roots to extend downward throughout the soil and shoots to extend upward to increase the plants exposure to light. Secondary growth allows for the plant to grow into thickness. Lateral meristems known as the vascular cambium and cork cambium are responsible for secondary growth.

In woody plants, primary growth is followed by secondary growth, which allows the plant stem to increase in thickness or girth. Secondary vascular tissue is added as the plant grows, as well as a cork layer.

In some plants the roots perform certain additional functions in order to meet some special needs. These are called secondary functions of the roots. In order to perform these special functions the roots show modification in their structure accordingly.

The primary growth occurs by the action of the apical meristem while the secondary growth occurs by the action of the cambium. The primary growth increases the length of the plant while the secondary growth increases the diameter of the plant.

All plant cells have a primary cell wall; only some plant cells have secondary walls. Secondary wall is impervious to water due to lignin: water can not flow in or out of a cell except when there is an opening. Cavities (openings) in the secondary wall, water flows through pits.

: growth in plants that results from the activity of a cambium producing increase especially in diameter, is mainly responsible for the bulk of the plant body, and supplies protective, supporting, and conducting tissue — compare primary growth.

After primary growth, lateral meristem becomes active and results in the formation of secondary permanent tissues. This is called the secondary growth. The lateral meristems are the lateral vascular cambium and cork cambium. They are formed only on dicots.

The thickening of the stem that occurs in secondary growth is due to the formation of secondary phloem and secondary xylem by the vascular cambium, plus the action of cork cambium, which forms the tough outermost layer of the stem. The cells of the secondary xylem contain lignin, which provides hardiness and strength.

The herbaceous plants only undergo primary growth. But, woody plants undergo both primary and secondary growth. The apical meristem causes the primary growth whereas the lateral meristem causes the secondary growth of the plant.

Primary Growth: The epidermis, cortex, and the primary vascular tissues are developed during the primary growth. Secondary Growth: The bark, periderm, lenticels, secondary phloem, and secondary xylem are developed during the secondary growth.