Tissues
A tissue is a group of cells having a common origin and usually performing a common function. Based on cell’s capability to divide, tissues are classified into two main groups which are as follows:
1. Meristematic and
2. Permanent tissues.
Meristematic Tissues: Cells in the meristematic tissue are capable of dividing. Meristematic tissues are found in those regions which need to grow continuously. For example, root tips and stem tips contain meristematic tissues. Meristematic tissues are of following types:
(a). Primary Meristems and
(b) Secondary Meristems
1. Primary Meristems: Primary meristems appear early in the life of a plant and are responsible for the formation of primary plant body. Primary growth involves development of new parts of a plant and growth in length of a particular part. Primary meristems are of two types:
(a). Apical Meristem: They are found in root tips and stem tips. In stems during the formation of leaves and elongation of stem, some cells are left behind from shoot tip and constitute the axillary bud. Such buds are capable of forming a branch or a flower.
(b). Intercalary Meristem: They are found between mature tissues. They occur in grasses and regenerate parts removed by the grazing herbivores.
Permanent Tissues:
After divisions of cells in both primary and as well as secondary meristems, the newly formed cells become structurally and functionally specialized and lose the ability to divide. Such cells are termed permanent or mature cells and constitute the permanent tissues. During the formation of the primary plant body, specific regions of the apical meristem produce dermal tissues, ground tissues and vascular tissues. Permanent tissues are of two types:
1. Simple Tissues and
2. Complex Tissues
1. Simple Tissues: A simple tissue is made of only one type of cells. Simple tissues are of following types:
(a). Parenchyma
(b). Collenchyma
(c). Sclerenchyma
Parenchyma: