·       I.  Apical meristem

Apical meristem is found at the tips of the roots, stems and branches. It plays a major role in the increase of plant length. It is divided into three zones namely protoderm, procambium and ground meristem. Protoderm gives rise to epidermal tissue. Procambium gives rise to primary vascular tissue and ground stem gives rise to cortex and pith. Apical meristem with two to three leaf primordia constitutes the apex.

II.  Intercalary meristem

Intercalary meristems is present in the nodal region and is very prominently found in the monocotyledons, e.g., grasses. The name itself represents that intercalary meristems are found in between the permanent tissues. It is responsible for the elongation of nodes.

III.  Lateral meristem

The meristem that is present along the longitudinal axis of stem and root is called lateral meristem, for example, vascular cambium and cork cambium. It produces secondary meristem tissues, which result in the thickening of stem and root.

3.  Establishment of pathogen free plants

The plants infected with bacteria and fungi can be treated by bactericidal and fungicidal compounds, there is no commercially available treatment to cure virus-infected plants. A large numbers of viruses are not transmitted through seeds. Therefore, it would be possible to obtain virus free plants from infected individuals by using seeds as propagules. However, genetic variation often occurs from the sexually reproduced plants when propagated by seeds. Generally, clonal multiplication of cultivars can be achieved by vegetative propagation. However, where the entire population of the clone is infected the only way to obtain pathogen-free stock is to eradicate the pathogen from vegetative parts of the plants and regenerate full plants from such tissues. Once pathogen free plants are obtained they can be multiplied indefinitely under conditions which would protect them from chance reinfection.