Plant Tissue

Tissue: The group of cells having common origin, and usually perform a common function.

(A) Meristematic tissue: Growing regions of the plants are called Meristem. Meristematic tissue have capability of cell division. Daughter cells formed out. It grow and constitute the different parts of the plant. This process continues till the life-span of the plant.

Specific features of the Meristematic tissues are as follows –

1. It is round, oval or multisided.

2. Its wall is thin and cytoplasm is homogeneous.

3. Cell contains dense cytoplasm and a single large nucleus.

4. There is lack of inter-cellular spaces between the cells.

Apical Meristems: These tissues are found in the root and stem apex and the initial growth (specially length) of the plants take place due to these tissue.

Lateral Meristems: Due to the division in these tissue growth in the girth of roots and stems takes place. Hence, it increases the width of the root and stem.

Intercalary Meristems: They are located at the base of internode. In fact, this is the remains of the Apical Meristems, which is divided by the incoming of permanent tissues in the centre. Plants increase its length by the activity of this. Its importance is for those plants whose apical parts are eaten by vegetarian animals. After being eaten the plants grow with the help of intercalary meristems only. Like – grass.

(B) Permanent tissue : Permanent tissues are made of those mature tissue which have lost the capicity of cell division. These tissues attain a definite forms at different places for a definite function. Cells of permanent tissue may be alive or dead.

(i) Simple permanent tissue: If permanent tissue is made up of similar types of cells, it is called simple tissue. There are three main types of simple tissue.

(a) Parenchyma : Cells of parenchyma are thin walled and unspecialized, used for multiple purpose in plant. This found in the inner layer of leaves called the mesophyll. These cells are photosynthetic. These cells are also found in covering of roots and stems. It is also found in soft part of fruit.

(b) Collenchyma : The cells of collenchyma are elongated having thick cell wall help to hold up the plant. It also provide flexibility to stems allowing them to bend.

(c) Sclerenchyma : The cells of sclerenchyma are dead having thick cell wall and become inflexible providing mechanical strength to the plant.

(ii) Complex permanent tissue: If the permanent tissue is made up of more than one kinds of tissue working together, it is called complex tissue.

Their are two main type of complex tissue.

(a) Xylem : Xylem is a conducting tissue found in vascular plants made up of tracheids, vesseles, xylemparenchyma cells and xylem fibers. The main function of xylem are –

Xylem help in transportation of water and minerals from the soil to the stems and leaves.

It provides mechanical strength to the plant.

Xylem is wood, which is a valuable raw materials.

The first formed primary xylem elements are called protoxylem.

The second formed primary xylem elements are called metaxylem.

In stem protoxylem lies towards the centre and metaxylem lies towards periphery. This type of arrengement is called endarch.

The determination of age of the plants is done by counting annual rings of xylem tissue this is called Dendrochronology.

(b) Phloem: It is a living conducting tissue made up of sieve element, companion cells, parenchyma cells and phloem fiber.

The main function of phloem are –

It conduct soluble organic compound from leaves to different part of plant. This kind of transport process is called translocation.

Phloem is the innermost layer of bark.

Companion cells of phloem are unique to angiosperm.

Husk of coconut is made up of sclerenchyma tissue.

In aquatic plant there are large air sac which give them buoyancy effect are surrounded by parenchymatous tissue.

Fibres in relation to plant anatomy are responsible for conduction and mechanical support.

In the middle layer of root apical meristem, is periblem which gives rise the cortex.

The wood is actually a secondary xylem.

Transpiration : It is a process of loss of water from the aerial part of plant in the form of water vapour.

The cells which are closely associated and interacting with guard cells are subsidiary cells.

Transpiration keeps the plant and their surrounding cool.

The process of the escape of liquid from the tip of leaf is called guttation.

Rate of transpiration can be measured by Ganong’s Potometer.

Note: Cotton fibers are made up of cellulose.

Silver fiber revolution is associated to cotton fiber.

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