What is a permanent tissue? Classify permanent tissues and describe them.
Answer:
Permanent tissues are derived from meristematic tissue but their cells have lost the power of division and have attained their definite forms.
Permanent tissues are classified into the following two types:
- Simple permanent tissue
- Complex permanent tissue
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Simple permanent tissues: These tissues are composed of cells which are structurally and
functionally similar.
Simple permanent tissues are further classified into the following three types:
- Parenchyma: Parenchyma forms the bulk of the plant body. Parenchyma cells are living and possess the power of division.
- Collenchyma: Collenchyma tissue is also living. It is characterised by the deposition of extra cellulose at the corners of the cells.
- Sclerenchyma: Sclerenchyma cells are dead cells and they are devoid of protoplasm. The cell walls of sclerenchyma are largely thickened with deposition of lignin.
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Complex permanent tissues: The complex tissues consist of more than one type of cells
having a common origin. All these cells coordinate to perform a common function.
Complex tissues are of the following two types:
- Xylem: Xylem is a vascular and mechanical tissue. It is a conducting tissue. Xylem is composed of four different types of cells:
- Tracheids
- Vessels
- Xylem parenchyma
- Xylem sclerenchyma.
Except xylem parenchyma, all other xylem elements are dead and bounded by thick lignified walls.
- Phloem: Like xylem, phloem is also vascular but has no mechanical function. Phloem is composed of following four elements:
- Sieve tubes
- Companion cells
- Phloem parenchyma
- Phloem fibres.
Except phloem fibres, all other phloem elements are living.
Xylem and phloem are both conducting tissues and are also known as vascular tissues. Together, both of them constitute vascular bundle.