Tissues

• Plant tissue system links different organs of plants.
• A plant tissue is made up of group of cells that may be either similar or dissimilar in structure, function and origin.
• Plants of higher level show this level of cellular organization.
• Plant tissues are divided into two types of tissue:
  • Meristematic tissue
  • Permanent tissue

Meristematic Tissues (Meristems)

STRUCTURE:

• They may be spherical, oval, polygonal or rectangular in shape.
• They are compactly arranged and do not contain any intercellular space between them.
• They lack vacuoles.
• Cells of meristematic tissue are very active.
• They have dense cytoplasm, thin cellulose walls and prominent nuclei.

FUNCTION:

• Cells of meristems divide continuously.
• Cells help in increasing the length and width of the plant.
• Cells help in growth of the plant.
• The place of injury in plants is healed up by the formation of new cells by meristems.

OCCURRENCE:

• They are found in the growing regions of the plant, like in the tips and nodes of plant parts like stems, branches, roots and shoots.
• According to the position of  the meristematic tissues, they are divided into three parts:
  • Apical
  • Lateral
  • Intercalary

Apical meristems:

• Occurrence: These are situated at the growing tip of stems and roots, i.e. at shoot apex and root apex. Apical meristems are also found at apices of the leaves.
• Function: They bring about the elongation of the root and stem which leads to the primary growth.

Lateral meristems:

• Occurrence: These are found beneath the bark and in vascular bundles of dicot roots and stems.
• Function: It causes the organ to increases in diameter and girth. This is called secondary growth.

Intercalary meristems:

Occurrence: They are located at the base of leaves or internode. e.g. stems of grasses and other monocots.
Function: They produce an increase in the length of an organ such as leaves and internodes.

Permanent Tissues:

• Cells derived from division of meristematic tissue take up specific role and lose the ability to divide.
• This results in the formation of permanent tissue.
• Their characteristics include:
  • Thin living cells or thick dead cells
  • Intercellular spaces which are either present or absent
  • Less dense cytoplasm where single large vacuole is embedded
• Different types of permanent tissues are formed due to differences in their specialization.

Permanent tissues can be of two forms:

• Simple
• Complex

Difference between merismatic tissue and permanent tissue: