Chapter 1 - Permanent Tissues in Plants

 PERMANENT TISSUES  IN PLANTS

These tissues are derived from merismatic tissues ,now that they have lost the power of division and have attained a permanent form.They can be  divided into 2 forms

1.  Simple  Permanent Tissues
2.  Complex Permanent Tissaues

Simple  Permanent Tissues:  They  are made up of  cells which are structurally and functionally similar.Thus these tissues are made up of one type of cells.

• Parenchyma
• Collenchyma
• Sclerenchyma

1. Parenchyma: living, isodiametric, cell wall is thin, intercellular spaces are abundant.
1. Occurrence: stem ,roots,leaves,flowers and fruits.
2. Functions:
1. packing tissue,
2. food storage
3. their intercellular air spaces allow gaseous exchange.
4. storage of waste materials
5. If chloroplast is present they can perform photosynthesis.
6. In aquatic plant they are filled with air and give buoyancy to the plant thus help them to float in water.
7. In xerophytes ie   arid plant   parenchyma acts as water storage tissue.
2. Collenchyma : living , similar to parenchyma except that it shows extra deposition of cellulose at the corners of the cells.
1. Occurrence : occurs below the  epidermis of dicotyledonous stems and petiole,midribs of dicot leaves,  absent in monocots stems ,roots and leaves.
2. Functions: mechanical  support and elasticity.
3. Sclerenchyma :  dead cells, and devoid of protoplasm.They cell walls are extensively thickened with deposition of lignin.Intercellular cell space is also absent
• the cell of sclerenchyma are of two type   FIBRE  and  SCLEREIDS
1. Occurrence : they are found in stems, roots, veins of leaves,hard coverings of seeds  and nuts.
2. Functions: mainly mechanical and protective in function.

                                           COMPLEX PERMANENT TISSUES

The complex tissues  consist of more than one type of cells.These cells coordinate to perform a common function.They are of two types in plants.

• Xylem
• Phloem

Both these cells are conducting tissues,together both of them are called vascular bundles.

Xylem:  It is a vascular and mechanical tissue. It is composed of four different types.

• Tracheids : elongated cells with tapering ends.water pas through pits from one cell to other.
• Vessels  : (most important),very long tube like stucture, placed end to end
• Xylem Parenchyma : (only living cells),stores food and helps in lateral conduction of water
• Xylem Sclerenchyma: 

Function: main function of xylem is to transport water and minerals from roots to different parts of the shoots.


Phloem:  It contains tubes  but have no mechanical function. It is composed of four different elements.

• Sieve tubes: slender, ,tube like structure,placed ,end to end,their ,end walls are perforated by numerous pores and are called sieve plates.
• Companion cells: generally associated with sieve tubes,small thin walled,has ,dense cytoplasm with large elongated nucleus.
• Phloem parenchyma:
• Phloem Fibres: (only dead cells)

Function: Phloem transport photosyntetically prepared food materials from the leaves to the storage organs  and  from their to active growing parts of the plants.