### Theory:

Points to remember:
Tissue: A Group of cells positioned and designed to perform a particular function is called a tissue.

Organ: An organ is a structure made up of a collection of tissues that carry out specialized functions.

Types of tissues in plants: They are mainly made up of vegetative tissues and reproductive tissues.

Classification of plant tissue: In general, plant tissues are classified into two types, namely meristems or meristematic tissues and permanent tissues.

Meristematic tissue: Meristems actively divide tissues of the plant responsible for primary (elongation) and secondary (thickness) growth of the plant.

Process of Differentiation:

$$\text{Meristematic tissue}$$     $$\xrightarrow{\small{\text{Differentiation process}}}$$      $$\text{Permanent Tissues}$$
Classification of Permanent tissue: Permanent tissues are classified into two types simple tissue and complex tissue.

Simple tissue: They are homogeneous - composed of structurally and functionally similar cells—e.g., Parenchyma, Collenchyma and Sclerenchyma.

Complex tissue: They are made up of more than one type of cells (Heterogenous) that work together as a unit; they are Xylem and Phloem.
Glossary:
Aerenchyma: Cortex of submerged roots of certain swamp plants aerating cortical tissue in floating portions of some aquatic plants.

Collenchyma: It is a peripheral supporting tissue with cells more or less elongated and thickened either at the angles or on walls adjoining intercellular spaces or tangentially.

Companion cell: A narrow cell retaining its nucleus derived from a cell giving rise to a sieve tube element in angiosperms' phloem.

Intercalary meristem: It is situated between regions of permanent tissue at the base of nodes and leaves in many monocotyledons.

Isodiametric: Having an equal diameter of cells or other structures.

Meristem tissue: Formed of cells all capable of diversification as found at growing points, meristematic tissue

Parenchyma: They contain living cells with soft and thin-walled, that may vary in structure and function as pith or mesophyll.

Phloem parenchyma: Thin-walled parenchyma associated with sieve tube of phloem.

Sclerenchyma: Plant tissue of thickened end of the hard cells or vessels

Xylem woody tissue: Lignified portion of vascular bundle.