1. Primary growth is the method by which roots and shoots are elongated in all vascular plants.
Contrary to animals, plants exhibit indeterminate growth, meaning that under ideal conditions and presence of resources, plants grow and add new organs continuously. Plants have two distinct types of growth: the primary and secondary growth. Primary growth is achieved through cell division and results in the elongation of the plant both above ground and below ground. Therefore, primary growth involves cell division at the tips of roots and shoots resulting in their elongation.
2. Primary growth is accomplished by two cylinders of dividing cells called apical meristems.
Plants' indeterminate growth is achieved through specialized tissues which have continuous cellular division and growth and are called meristems. Apical meristems are found at the tips of roots and shoots and are responsible for the elongation of the plant's roots and shoots. Therefore, apical meristems are the main tissue responsible for primary growth.
3. Secondary growth is accomplished by groups of undifferentiated cells at the tips of the roots and shoots called lateral meristems.
Apart from primary growth, some plants also exhibit secondary growth, which involves the increase in the width and thickness of the plant. Secondary growth is achieved through lateral meristems, which are groups of undifferentiated cells with high cell division activity. The difference is that these cells grow outward, resulting in the widening of the plant.
4. The majority of growth in width is due to increases in the number of cells added by the vascular cambium.
Lateral meristems are also called cambiums, a term referring to growth through the addition of tissue layers. There are two cambiums which are critical to secondary growth: vascular and cork cambium. Vascular cambium forms vascular tissue attributing to the plant's support and transport of water and nutrients. The cells of the vascular cambium divide and produce the secondary xylem and phloem. This causes a growth in width.
5. Cork is the method by which woody plants grow in thickness.
As explained above, secondary growth is achieved through two cambiums (cork and vascular cambium). In woody plants, cork cambium produces tough and thickened cork cells which participate in the increase of the plant's thickness. In addition, cork cells protect and insulate the plant. More specifically, cork cells protect from pathogens, insects and incidents of fire and reduce water loss.
