Plants can grow indefinitely meaning throughout their lives. Plants can achieve this because of the presence of a tissue which is young as always. The tissue is called meristem which is derived from a Greek word called ‘to divide’. A small portion of one of them can develop into a new plant.
Meristem tissue is capable of dividing into new cells. Plant hormones are said to control the regulation of cell division. Meristem tissue normally occurs in the roots, shoots and at the junction of leaf and stem. It can occur elsewhere too. For instance when a leaf is cut off, both the cutting and the plant from which the cutting was done may still contain meristematic tissue. This means both have the capacity for growth.
Even more interesting is that the cells from one part of a plant (for instance a leaf) can turn into cells of a different part such as roots. Though a leaf by itself has no perpetually young tissue, its cells can take up new roles changing their original function. That is why just a single leaf from an African violet can under the right conditions develop into a new beauty flowering on its own.
Depending on where they are located in the plant, they are mainly classified as apical, lateral and intercalary meristem. Apical ones referred to as primary meristem are located on root and shoot tips. These are found to play a vital role in increasing the length of roots and shoots. Lateral ones also called secondary meristem are found just under the root or shoot surface. Lateral meristem is responsible for the growth in the tree trunk’s diameter. Intercalary meristem refers to tissue in between the leaf and the stem.