Name of TeacherDr Brijesh Pathak Designation Assistant Professor

Name of Teacher-Dr. Brijesh Pathak Designation- Assistant Professor Address-University College, Dhilwan, Tapa Subject Name- Botany (Tissues) B. Sc. (Medical)-Semester IV

Definition of Tissues A group of cells with similar origin, structure and function is called tissue. Classification of Plant Tissues- • Meristematic tissue-Meristematic tissue may be defined as a group of living cells which are located at specific location • These divide continuously to add new cells to the plant body. • Permanent tissues-Permanent tissue may be defined as a group of living or dead cells formed by meristematic tissue • They have lost their ability to divide and have permanently placed at fixed position in plant body.

Characteristics of meristematic tissues • Continuously dividing cells. • Cells are small and isodiametric. • The cell wall is thin and made up of cellulose. • Cytoplasm is abundant. • Nuclei are large. • Vacuoles are absent • Lack inter-cellular spaces. • Metabolic activities are at high rate.

Classification of meristematic tissue A) Based on Origin and development (a) Promeristem-The meristem where foundation of new organs is laid down is called promeristem. • They occupy at the tips of stem and root. • It differentiates into primary meristem. (b) Primary meristematic tissue-It originate from promeristem. • Remains meristematic from the embryonic condition throughout entire plant life at the growing apices of roots, stems. (c) Secondary meristematic tissue-It develops from primary permanent tissue.

B)Based on location in plant body 1. Apical meristem Position: At the root tip and shoot tip. Function: To increase in length of the axis. 2. Lateral meristem Position: On the lateral side of stem and root. Function: To increase in diameter of plant. 3. Intercalary meristem Position: At the base of the leaf/internodes/ leaf. Function: To increase the length of the plant or its organs.

C)Based on function • Protoderm- Developing into epidermis. • Procambium- Developing into vascular tissue. • Ground meristem- Developing into ground tissue and pith I) Simple Tissues

TYPES OF SCLERENCHYMA i) Fibres • Fibres are long, thick and lignified cells usually with pointed or blunt ends. • Usually occur in bundles. • Provide tensile strength, flexibility and elasticity to plant or plant's parts. • Originate from meristematic cells. ii) Sclereids ( Also known as stone cells) • Most common in fruits and seeds • Cells are isodiametric, spherical, in shape, have thick lignified secondary cell wall. • Provide mechanical strength and rigidity. • Formed by secondary thickening of parenchyma cells.

Complex permanent tissue A) Xylem : • Term introduce by Nageli(1858) • Greek xylos meaning wood. Elements of xylem: 1)Tracheary elements: - These are nonliving cells, provide support and conduct water. Two types of Tracheary elements (a)Tracheids: elongate, tube like cell, tapering, hard lignified walls. (b)Vessels members: long, tube-like structures with lignified walls. (2)Fibres: thick walls, evolve from tracheids and provide mechanical strength.

Two types of Fibres (a)Fibre-tracheids: medium thickness walls, have reduced boardered pits. (b)Libriform fibres: very thick walls, have reduced simple pits. (3) Xylem Parenchyma: living cells, in woody plants, store of food in starch form. Two types: (a)Axial parenchyma: derived from fusiform initials, have tracheary elements and fibres. (b)Ray parenchyma: derived from ray initials of cambium, xylem ray cells.

b) Pholem : • Term introduce by Nageli(1853) • Greek word Meaning Bark • Bark is a non technical term describing all tissues outside secondary xylem • Bark includes secondary pholem, primary pholem, cortex and periderm Elements of Pholem: - • Sieve Elements • Companion Cells • Pholem Parenchyma • Pholem Fibres

Sieve Elements: - • Living cells in the pholem • Presence of Protoplasm • No Lignified Walls • Two types namely sieve cells and sieve tubes • Sieve cells occur in Pteridophytes and Gymnosperms and consists of elongated cells with inclined end walls • Sieve elemnets are characteristics of Angiosperms with longitudinal arrangement of cells Companion Cells: - • Specialised Parenchyma cells are called as companion cells

• Companion cells are metabolically active and are connected to sieve tubes by plasmodesmata Pholem Parenchyma: - • Thin Walled • Living Cells • Parenchymatous • Act as storage tissue Pholem Fibres: - • Dead Cells • Lignified