- A tissue is a group of cells having a common origin and usually performing a common function.
- Tissues are classified into two main groups, namely, meristematic and permanent tissues based on whether the cells being formed are capable of dividing or not.
- Growth in plants is largely restricted to specialised regions of active cell division called meristems.
- The meristems which occur at the tips of roots and shoots and produce primary tissues are called apical meristems.
- Root apical meristem occupies the tip of a root while the shoot apical meristem occupies the distant most region of the stem axis.
- During the formation of leaves and elongation of stem, some cells ‘left behind’ from shoot apical meristem, constitute the axillary bud, which are present in the axils of leaves and form a branch or a flower.
- The meristem which occurs between mature tissues is known as intercalary meristem, which occurs in grasses and regenerated parts.
- Both apical meristems and intercalary meristems are primary meristems because they appear early in life of a plant and contribute to the formation of the primary plant body.
- The meristem that occurs in the mature regions of roots and shoots of many plants, appear later than primary meristem is called the secondary or lateral meristem.
For example- fascicular vascular cambium, interfascicular cambium and cork-cambium.
- The newly formed cells after cell division in both primary and as well as secondary meristems become specialised and lose the ability to divide, such cells are termed permanent or mature cells and constitute the permanent tissues.
- Specific regions of the apical meristem produce dermal tissues, ground tissues and vascular tissues, during the formation of the primary plant body.
Fig. Parts of meristem
- The tissues which are formed by the permanent or mature cells that do not divide further are called permanent tissues.
- Permanent tissues having all cells similar in structure and function are called simple tissues.
- Permanent tissues having many different types of cells are called complex tissues.
Fig. Permanent tissues