List Secondary meristems
1. Lateral meristems
2. Vascular cambium
3. Cork cambium
4. Interfascicular cambium
5. Phellogen (bark-forming tissue)
Secondary meristems are meristematic tissues that form after the primary growth of the plant has ceased. These meristems contribute to the secondary growth of plants, allowing them to increase in girth. The main secondary meristems in plants are:
1. Vascular Cambium: Found in woody plants, the vascular cambium is responsible for the production of new xylem and phloem cells. It produces secondary xylem to the inside, which contributes to the growth rings in the stem, and secondary phloem to the outside.
2. Cork Cambium (Phellogen): The cork cambium is a lateral meristem found in the outer layers of stems and roots. It produces cork cells, which are protective tissues that replace the epidermis in older stems and roots. The cork cells form the outermost layer of the bark.
3. Fusiform Initials: Found in the vascular cambium, fusiform initials are responsible for the formation of secondary xylem cells in elongated shapes. They differentiate into xylem cells that contribute to the growth of woody stems.
4. Ray Initials: Also found in the vascular cambium, ray initials are responsible for the formation of radial files of cells called rays. These rays function in the lateral transport of water, nutrients, and photosynthates within the woody stem.
These secondary meristems work together to contribute to the secondary growth of plants, helping them increase in girth, produce new conducting tissues, and protect their stems and roots.