Plant Tissue

Tissues are the group of cells similar in origin, structure and functions –

Meristematic tissues

• The growing regions of plants are called Meristem . These can produce daughter cell. It grows and constitute different parts of the plant. This process continues till the life-span of the plant.
  • The tissue is round, oval or multisided.
  • It’s wall is thin and cytoplasm is homogenous.
  • Cell contains large cytoplasm and a large nucleus.
  • There is lack of apaces between the cells.

Merismatic tissues are of three types –

1. Apical Meristems – These tissues are found in root and stem apex. Initial growth/length is because of these tissues.
2. Lateral Meristems – Due to the division in these tissues. It increases the width of root and stems.
3. Intercalary Meristems – These are remains of Apical Meristems, which are present in the base on internode due to incoming permanent tissues. It’s importance is in the plants whose apical part is eaten by the vegetarian animals. After being eaten the plants grow with the help of intercalary meristems only. Ex – grass.

Permanent tissues

• It is formed by those tissues which has lost the cell division capacity. These takes different forms in different places for different functions. Cells of permanent tissues may be alive or dead. It can be further classified into Simple and Complex tissues.

Simple permanent tissues –

If permanent tissues is made up of similar types of cells, it is called simple tissues. There are three main types of simple tissues –

1. Parenchyma – Cells of parenchyma are thin walled and unspecialized, used for multipurpose in plants. This found in inner layer of leaves called mesophyll and is photosynthetic. These are also covering of roots and stems. It is also found in soft part of fruit.
2. Collenchyma – The cells are elongated having thick cell wall help to hold up the plant. It also provide flexibility to stems allowing them tobend.
3. Sclerenchyma – The cells are dead having thick cell wall and become inflexible that provides mechanical strength to the plant.

Complex permanent tissues –

If the permanent tissue is made-up of more than one kinds f tissue working together, it is called complex tissues. There are two type of complex tissues –

Xylem	Phloem
Xylem is a conducting tissue found in vascular plants made up of tracheids, vesseles, xylem parenchyma cells and xylem fiber.	It is a living conducting tissue made up of sieve element, companion cells, parenchyma cells and phloem fiber.
Xylem helps in transportation of water and minerals from the soil to the stems and leaves.	Phloem conducts soluble organic compounds from leaves to different part of plant.
It provides mechanical strength to the plant.	This kind of transport process called translocation.
Xylem is a wood, which is a valuabel raw amterial.	Phloem is the innermost layer of bark.
The first formed primary xylem and secondary xylem is called protoxylem and metaxyem respectively.	Companian cells of phloem are unique to angiosperm.
In stem protoxylem lies in center and metaxylem is lies towards margin.
** The determination of age of the plants is done by counting annual rings of xylem tissue this is called “dendrochronology”.**